// SPDX-License-Identifier: MIT
/*
 * Copyright © 2014 Intel Corporation
 */

/**
 * DOC: Logical Rings, Logical Ring Contexts and Execlists
 *
 * Motivation:
 * GEN8 brings an expansion of the HW contexts: "Logical Ring Contexts".
 * These expanded contexts enable a number of new abilities, especially
 * "Execlists" (also implemented in this file).
 *
 * One of the main differences with the legacy HW contexts is that logical
 * ring contexts incorporate many more things to the context's state, like
 * PDPs or ringbuffer control registers:
 *
 * The reason why PDPs are included in the context is straightforward: as
 * PPGTTs (per-process GTTs) are actually per-context, having the PDPs
 * contained there mean you don't need to do a ppgtt->switch_mm yourself,
 * instead, the GPU will do it for you on the context switch.
 *
 * But, what about the ringbuffer control registers (head, tail, etc..)?
 * shouldn't we just need a set of those per engine command streamer? This is
 * where the name "Logical Rings" starts to make sense: by virtualizing the
 * rings, the engine cs shifts to a new "ring buffer" with every context
 * switch. When you want to submit a workload to the GPU you: A) choose your
 * context, B) find its appropriate virtualized ring, C) write commands to it
 * and then, finally, D) tell the GPU to switch to that context.
 *
 * Instead of the legacy MI_SET_CONTEXT, the way you tell the GPU to switch
 * to a contexts is via a context execution list, ergo "Execlists".
 *
 * LRC implementation:
 * Regarding the creation of contexts, we have:
 *
 * - One global default context.
 * - One local default context for each opened fd.
 * - One local extra context for each context create ioctl call.
 *
 * Now that ringbuffers belong per-context (and not per-engine, like before)
 * and that contexts are uniquely tied to a given engine (and not reusable,
 * like before) we need:
 *
 * - One ringbuffer per-engine inside each context.
 * - One backing object per-engine inside each context.
 *
 * The global default context starts its life with these new objects fully
 * allocated and populated. The local default context for each opened fd is
 * more complex, because we don't know at creation time which engine is going
 * to use them. To handle this, we have implemented a deferred creation of LR
 * contexts:
 *
 * The local context starts its life as a hollow or blank holder, that only
 * gets populated for a given engine once we receive an execbuffer. If later
 * on we receive another execbuffer ioctl for the same context but a different
 * engine, we allocate/populate a new ringbuffer and context backing object and
 * so on.
 *
 * Finally, regarding local contexts created using the ioctl call: as they are
 * only allowed with the render ring, we can allocate & populate them right
 * away (no need to defer anything, at least for now).
 *
 * Execlists implementation:
 * Execlists are the new method by which, on gen8+ hardware, workloads are
 * submitted for execution (as opposed to the legacy, ringbuffer-based, method).
 * This method works as follows:
 *
 * When a request is committed, its commands (the BB start and any leading or
 * trailing commands, like the seqno breadcrumbs) are placed in the ringbuffer
 * for the appropriate context. The tail pointer in the hardware context is not
 * updated at this time, but instead, kept by the driver in the ringbuffer
 * structure. A structure representing this request is added to a request queue
 * for the appropriate engine: this structure contains a copy of the context's
 * tail after the request was written to the ring buffer and a pointer to the
 * context itself.
 *
 * If the engine's request queue was empty before the request was added, the
 * queue is processed immediately. Otherwise the queue will be processed during
 * a context switch interrupt. In any case, elements on the queue will get sent
 * (in pairs) to the GPU's ExecLists Submit Port (ELSP, for short) with a
 * globally unique 20-bits submission ID.
 *
 * When execution of a request completes, the GPU updates the context status
 * buffer with a context complete event and generates a context switch interrupt.
 * During the interrupt handling, the driver examines the events in the buffer:
 * for each context complete event, if the announced ID matches that on the head
 * of the request queue, then that request is retired and removed from the queue.
 *
 * After processing, if any requests were retired and the queue is not empty
 * then a new execution list can be submitted. The two requests at the front of
 * the queue are next to be submitted but since a context may not occur twice in
 * an execution list, if subsequent requests have the same ID as the first then
 * the two requests must be combined. This is done simply by discarding requests
 * at the head of the queue until either only one requests is left (in which case
 * we use a NULL second context) or the first two requests have unique IDs.
 *
 * By always executing the first two requests in the queue the driver ensures
 * that the GPU is kept as busy as possible. In the case where a single context
 * completes but a second context is still executing, the request for this second
 * context will be at the head of the queue when we remove the first one. This
 * request will then be resubmitted along with a new request for a different context,
 * which will cause the hardware to continue executing the second request and queue
 * the new request (the GPU detects the condition of a context getting preempted
 * with the same context and optimizes the context switch flow by not doing
 * preemption, but just sampling the new tail pointer).
 *
 */
#include <linux/interrupt.h>

#include "i915_drv.h"
#include "i915_trace.h"
#include "i915_vgpu.h"
#include "gen8_engine_cs.h"
#include "intel_breadcrumbs.h"
#include "intel_context.h"
#include "intel_engine_pm.h"
#include "intel_engine_stats.h"
#include "intel_execlists_submission.h"
#include "intel_gt.h"
#include "intel_gt_irq.h"
#include "intel_gt_pm.h"
#include "intel_gt_requests.h"
#include "intel_lrc.h"
#include "intel_lrc_reg.h"
#include "intel_mocs.h"
#include "intel_reset.h"
#include "intel_ring.h"
#include "intel_workarounds.h"
#include "shmem_utils.h"

#define RING_EXECLIST_QFULL		(1 << 0x2)
#define RING_EXECLIST1_VALID		(1 << 0x3)
#define RING_EXECLIST0_VALID		(1 << 0x4)
#define RING_EXECLIST_ACTIVE_STATUS	(3 << 0xE)
#define RING_EXECLIST1_ACTIVE		(1 << 0x11)
#define RING_EXECLIST0_ACTIVE		(1 << 0x12)

#define GEN8_CTX_STATUS_IDLE_ACTIVE	(1 << 0)
#define GEN8_CTX_STATUS_PREEMPTED	(1 << 1)
#define GEN8_CTX_STATUS_ELEMENT_SWITCH	(1 << 2)
#define GEN8_CTX_STATUS_ACTIVE_IDLE	(1 << 3)
#define GEN8_CTX_STATUS_COMPLETE	(1 << 4)
#define GEN8_CTX_STATUS_LITE_RESTORE	(1 << 15)

#define GEN8_CTX_STATUS_COMPLETED_MASK \
	 (GEN8_CTX_STATUS_COMPLETE | GEN8_CTX_STATUS_PREEMPTED)

#define GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE	(0x1) /* lower csb dword */
#define GEN12_CTX_SWITCH_DETAIL(csb_dw)	((csb_dw) & 0xF) /* upper csb dword */
#define GEN12_CSB_SW_CTX_ID_MASK		GENMASK(25, 15)
#define GEN12_IDLE_CTX_ID		0x7FF
#define GEN12_CSB_CTX_VALID(csb_dw) \
	(FIELD_GET(GEN12_CSB_SW_CTX_ID_MASK, csb_dw) != GEN12_IDLE_CTX_ID)

/* Typical size of the average request (2 pipecontrols and a MI_BB) */
#define EXECLISTS_REQUEST_SIZE 64 /* bytes */

struct virtual_engine {
	struct intel_engine_cs base;
	struct intel_context context;
	struct rcu_work rcu;

	/*
	 * We allow only a single request through the virtual engine at a time
	 * (each request in the timeline waits for the completion fence of
	 * the previous before being submitted). By restricting ourselves to
	 * only submitting a single request, each request is placed on to a
	 * physical to maximise load spreading (by virtue of the late greedy
	 * scheduling -- each real engine takes the next available request
	 * upon idling).
	 */
	struct i915_request *request;

	/*
	 * We keep a rbtree of available virtual engines inside each physical
	 * engine, sorted by priority. Here we preallocate the nodes we need
	 * for the virtual engine, indexed by physical_engine->id.
	 */
	struct ve_node {
		struct rb_node rb;
		int prio;
	} nodes[I915_NUM_ENGINES];

	/*
	 * Keep track of bonded pairs -- restrictions upon on our selection
	 * of physical engines any particular request may be submitted to.
	 * If we receive a submit-fence from a master engine, we will only
	 * use one of sibling_mask physical engines.
	 */
	struct ve_bond {
		const struct intel_engine_cs *master;
		intel_engine_mask_t sibling_mask;
	} *bonds;
	unsigned int num_bonds;

	/* And finally, which physical engines this virtual engine maps onto. */
	unsigned int num_siblings;
	struct intel_engine_cs *siblings[];
};

static struct virtual_engine *to_virtual_engine(struct intel_engine_cs *engine)
{
	GEM_BUG_ON(!intel_engine_is_virtual(engine));
	return container_of(engine, struct virtual_engine, base);
}

static struct i915_request *
__active_request(const struct intel_timeline * const tl,
		 struct i915_request *rq,
		 int error)
{
	struct i915_request *active = rq;

	list_for_each_entry_from_reverse(rq, &tl->requests, link) {
		if (__i915_request_is_complete(rq))
			break;

		if (error) {
			i915_request_set_error_once(rq, error);
			__i915_request_skip(rq);
		}
		active = rq;
	}

	return active;
}

static struct i915_request *
active_request(const struct intel_timeline * const tl, struct i915_request *rq)
{
	return __active_request(tl, rq, 0);
}

static void ring_set_paused(const struct intel_engine_cs *engine, int state)
{
	/*
	 * We inspect HWS_PREEMPT with a semaphore inside
	 * engine->emit_fini_breadcrumb. If the dword is true,
	 * the ring is paused as the semaphore will busywait
	 * until the dword is false.
	 */
	engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state;
	if (state)
		wmb();
}

static struct i915_priolist *to_priolist(struct rb_node *rb)
{
	return rb_entry(rb, struct i915_priolist, node);
}

static int rq_prio(const struct i915_request *rq)
{
	return READ_ONCE(rq->sched.attr.priority);
}

static int effective_prio(const struct i915_request *rq)
{
	int prio = rq_prio(rq);

	/*
	 * If this request is special and must not be interrupted at any
	 * cost, so be it. Note we are only checking the most recent request
	 * in the context and so may be masking an earlier vip request. It
	 * is hoped that under the conditions where nopreempt is used, this
	 * will not matter (i.e. all requests to that context will be
	 * nopreempt for as long as desired).
	 */
	if (i915_request_has_nopreempt(rq))
		prio = I915_PRIORITY_UNPREEMPTABLE;

	return prio;
}

static int queue_prio(const struct i915_sched_engine *sched_engine)
{
	struct rb_node *rb;

	rb = rb_first_cached(&sched_engine->queue);
	if (!rb)
		return INT_MIN;

	return to_priolist(rb)->priority;
}

static int virtual_prio(const struct intel_engine_execlists *el)
{
	struct rb_node *rb = rb_first_cached(&el->virtual);

	return rb ? rb_entry(rb, struct ve_node, rb)->prio : INT_MIN;
}

static bool need_preempt(const struct intel_engine_cs *engine,
			 const struct i915_request *rq)
{
	int last_prio;

	if (!intel_engine_has_semaphores(engine))
		return false;

	/*
	 * Check if the current priority hint merits a preemption attempt.
	 *
	 * We record the highest value priority we saw during rescheduling
	 * prior to this dequeue, therefore we know that if it is strictly
	 * less than the current tail of ESLP[0], we do not need to force
	 * a preempt-to-idle cycle.
	 *
	 * However, the priority hint is a mere hint that we may need to
	 * preempt. If that hint is stale or we may be trying to preempt
	 * ourselves, ignore the request.
	 *
	 * More naturally we would write
	 *      prio >= max(0, last);
	 * except that we wish to prevent triggering preemption at the same
	 * priority level: the task that is running should remain running
	 * to preserve FIFO ordering of dependencies.
	 */
	last_prio = max(effective_prio(rq), I915_PRIORITY_NORMAL - 1);
	if (engine->sched_engine->queue_priority_hint <= last_prio)
		return false;

	/*
	 * Check against the first request in ELSP[1], it will, thanks to the
	 * power of PI, be the highest priority of that context.
	 */
	if (!list_is_last(&rq->sched.link, &engine->sched_engine->requests) &&
	    rq_prio(list_next_entry(rq, sched.link)) > last_prio)
		return true;

	/*
	 * If the inflight context did not trigger the preemption, then maybe
	 * it was the set of queued requests? Pick the highest priority in
	 * the queue (the first active priolist) and see if it deserves to be
	 * running instead of ELSP[0].
	 *
	 * The highest priority request in the queue can not be either
	 * ELSP[0] or ELSP[1] as, thanks again to PI, if it was the same
	 * context, it's priority would not exceed ELSP[0] aka last_prio.
	 */
	return max(virtual_prio(&engine->execlists),
		   queue_prio(engine->sched_engine)) > last_prio;
}

__maybe_unused static bool
assert_priority_queue(const struct i915_request *prev,
		      const struct i915_request *next)
{
	/*
	 * Without preemption, the prev may refer to the still active element
	 * which we refuse to let go.
	 *
	 * Even with preemption, there are times when we think it is better not
	 * to preempt and leave an ostensibly lower priority request in flight.
	 */
	if (i915_request_is_active(prev))
		return true;

	return rq_prio(prev) >= rq_prio(next);
}

static struct i915_request *
__unwind_incomplete_requests(struct intel_engine_cs *engine)
{
	struct i915_request *rq, *rn, *active = NULL;
	struct list_head *pl;
	int prio = I915_PRIORITY_INVALID;

	lockdep_assert_held(&engine->sched_engine->lock);

	list_for_each_entry_safe_reverse(rq, rn,
					 &engine->sched_engine->requests,
					 sched.link) {
		if (__i915_request_is_complete(rq)) {
			list_del_init(&rq->sched.link);
			continue;
		}

		__i915_request_unsubmit(rq);

		GEM_BUG_ON(rq_prio(rq) == I915_PRIORITY_INVALID);
		if (rq_prio(rq) != prio) {
			prio = rq_prio(rq);
			pl = i915_sched_lookup_priolist(engine->sched_engine,
							prio);
		}
		GEM_BUG_ON(i915_sched_engine_is_empty(engine->sched_engine));

		list_move(&rq->sched.link, pl);
		set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);

		/* Check in case we rollback so far we wrap [size/2] */
		if (intel_ring_direction(rq->ring,
					 rq->tail,
					 rq->ring->tail + 8) > 0)
			rq->context->lrc.desc |= CTX_DESC_FORCE_RESTORE;

		active = rq;
	}

	return active;
}

struct i915_request *
execlists_unwind_incomplete_requests(struct intel_engine_execlists *execlists)
{
	struct intel_engine_cs *engine =
		container_of(execlists, typeof(*engine), execlists);

	return __unwind_incomplete_requests(engine);
}

static void
execlists_context_status_change(struct i915_request *rq, unsigned long status)
{
	/*
	 * Only used when GVT-g is enabled now. When GVT-g is disabled,
	 * The compiler should eliminate this function as dead-code.
	 */
	if (!IS_ENABLED(CONFIG_DRM_I915_GVT))
		return;

	atomic_notifier_call_chain(&rq->engine->context_status_notifier,
				   status, rq);
}

static void reset_active(struct i915_request *rq,
			 struct intel_engine_cs *engine)
{
	struct intel_context * const ce = rq->context;
	u32 head;

	/*
	 * The executing context has been cancelled. We want to prevent
	 * further execution along this context and propagate the error on
	 * to anything depending on its results.
	 *
	 * In __i915_request_submit(), we apply the -EIO and remove the
	 * requests' payloads for any banned requests. But first, we must
	 * rewind the context back to the start of the incomplete request so
	 * that we do not jump back into the middle of the batch.
	 *
	 * We preserve the breadcrumbs and semaphores of the incomplete
	 * requests so that inter-timeline dependencies (i.e other timelines)
	 * remain correctly ordered. And we defer to __i915_request_submit()
	 * so that all asynchronous waits are correctly handled.
	 */
	ENGINE_TRACE(engine, "{ reset rq=%llx:%lld }\n",
		     rq->fence.context, rq->fence.seqno);

	/* On resubmission of the active request, payload will be scrubbed */
	if (__i915_request_is_complete(rq))
		head = rq->tail;
	else
		head = __active_request(ce->timeline, rq, -EIO)->head;
	head = intel_ring_wrap(ce->ring, head);

	/* Scrub the context image to prevent replaying the previous batch */
	lrc_init_regs(ce, engine, true);

	/* We've switched away, so this should be a no-op, but intent matters */
	ce->lrc.lrca = lrc_update_regs(ce, engine, head);
}

static bool bad_request(const struct i915_request *rq)
{
	return rq->fence.error && i915_request_started(rq);
}

static struct intel_engine_cs *
__execlists_schedule_in(struct i915_request *rq)
{
	struct intel_engine_cs * const engine = rq->engine;
	struct intel_context * const ce = rq->context;

	intel_context_get(ce);

	if (unlikely(intel_context_is_closed(ce) &&
		     !intel_engine_has_heartbeat(engine)))
		intel_context_set_banned(ce);

	if (unlikely(intel_context_is_banned(ce) || bad_request(rq)))
		reset_active(rq, engine);

	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
		lrc_check_regs(ce, engine, "before");

	if (ce->tag) {
		/* Use a fixed tag for OA and friends */
		GEM_BUG_ON(ce->tag <= BITS_PER_LONG);
		ce->lrc.ccid = ce->tag;
	} else {
		/* We don't need a strict matching tag, just different values */
		unsigned int tag = __ffs(engine->context_tag);

		GEM_BUG_ON(tag >= BITS_PER_LONG);
		__clear_bit(tag, &engine->context_tag);
		ce->lrc.ccid = (1 + tag) << (GEN11_SW_CTX_ID_SHIFT - 32);

		BUILD_BUG_ON(BITS_PER_LONG > GEN12_MAX_CONTEXT_HW_ID);
	}

	ce->lrc.ccid |= engine->execlists.ccid;

	__intel_gt_pm_get(engine->gt);
	if (engine->fw_domain && !engine->fw_active++)
		intel_uncore_forcewake_get(engine->uncore, engine->fw_domain);
	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_IN);
	intel_engine_context_in(engine);

	CE_TRACE(ce, "schedule-in, ccid:%x\n", ce->lrc.ccid);

	return engine;
}

static void execlists_schedule_in(struct i915_request *rq, int idx)
{
	struct intel_context * const ce = rq->context;
	struct intel_engine_cs *old;

	GEM_BUG_ON(!intel_engine_pm_is_awake(rq->engine));
	trace_i915_request_in(rq, idx);

	old = ce->inflight;
	if (!old)
		old = __execlists_schedule_in(rq);
	WRITE_ONCE(ce->inflight, ptr_inc(old));

	GEM_BUG_ON(intel_context_inflight(ce) != rq->engine);
}

static void
resubmit_virtual_request(struct i915_request *rq, struct virtual_engine *ve)
{
	struct intel_engine_cs *engine = rq->engine;

	spin_lock_irq(&engine->sched_engine->lock);

	clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
	WRITE_ONCE(rq->engine, &ve->base);
	ve->base.submit_request(rq);

	spin_unlock_irq(&engine->sched_engine->lock);
}

static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
	struct intel_engine_cs *engine = rq->engine;

	/*
	 * After this point, the rq may be transferred to a new sibling, so
	 * before we clear ce->inflight make sure that the context has been
	 * removed from the b->signalers and furthermore we need to make sure
	 * that the concurrent iterator in signal_irq_work is no longer
	 * following ce->signal_link.
	 */
	if (!list_empty(&ce->signals))
		intel_context_remove_breadcrumbs(ce, engine->breadcrumbs);

	/*
	 * This engine is now too busy to run this virtual request, so
	 * see if we can find an alternative engine for it to execute on.
	 * Once a request has become bonded to this engine, we treat it the
	 * same as other native request.
	 */
	if (i915_request_in_priority_queue(rq) &&
	    rq->execution_mask != engine->mask)
		resubmit_virtual_request(rq, ve);

	if (READ_ONCE(ve->request))
		tasklet_hi_schedule(&ve->base.sched_engine->tasklet);
}

static void __execlists_schedule_out(struct i915_request * const rq,
				     struct intel_context * const ce)
{
	struct intel_engine_cs * const engine = rq->engine;
	unsigned int ccid;

	/*
	 * NB process_csb() is not under the engine->sched_engine->lock and hence
	 * schedule_out can race with schedule_in meaning that we should
	 * refrain from doing non-trivial work here.
	 */

	CE_TRACE(ce, "schedule-out, ccid:%x\n", ce->lrc.ccid);
	GEM_BUG_ON(ce->inflight != engine);

	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
		lrc_check_regs(ce, engine, "after");

	/*
	 * If we have just completed this context, the engine may now be
	 * idle and we want to re-enter powersaving.
	 */
	if (intel_timeline_is_last(ce->timeline, rq) &&
	    __i915_request_is_complete(rq))
		intel_engine_add_retire(engine, ce->timeline);

	ccid = ce->lrc.ccid;
	ccid >>= GEN11_SW_CTX_ID_SHIFT - 32;
	ccid &= GEN12_MAX_CONTEXT_HW_ID;
	if (ccid < BITS_PER_LONG) {
		GEM_BUG_ON(ccid == 0);
		GEM_BUG_ON(test_bit(ccid - 1, &engine->context_tag));
		__set_bit(ccid - 1, &engine->context_tag);
	}

	lrc_update_runtime(ce);
	intel_engine_context_out(engine);
	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
	if (engine->fw_domain && !--engine->fw_active)
		intel_uncore_forcewake_put(engine->uncore, engine->fw_domain);
	intel_gt_pm_put_async(engine->gt);

	/*
	 * If this is part of a virtual engine, its next request may
	 * have been blocked waiting for access to the active context.
	 * We have to kick all the siblings again in case we need to
	 * switch (e.g. the next request is not runnable on this
	 * engine). Hopefully, we will already have submitted the next
	 * request before the tasklet runs and do not need to rebuild
	 * each virtual tree and kick everyone again.
	 */
	if (ce->engine != engine)
		kick_siblings(rq, ce);

	WRITE_ONCE(ce->inflight, NULL);
	intel_context_put(ce);
}

static inline void execlists_schedule_out(struct i915_request *rq)
{
	struct intel_context * const ce = rq->context;

	trace_i915_request_out(rq);

	GEM_BUG_ON(!ce->inflight);
	ce->inflight = ptr_dec(ce->inflight);
	if (!__intel_context_inflight_count(ce->inflight))
		__execlists_schedule_out(rq, ce);

	i915_request_put(rq);
}

static u64 execlists_update_context(struct i915_request *rq)
{
	struct intel_context *ce = rq->context;
	u64 desc = ce->lrc.desc;
	u32 tail, prev;

	/*
	 * WaIdleLiteRestore:bdw,skl
	 *
	 * We should never submit the context with the same RING_TAIL twice
	 * just in case we submit an empty ring, which confuses the HW.
	 *
	 * We append a couple of NOOPs (gen8_emit_wa_tail) after the end of
	 * the normal request to be able to always advance the RING_TAIL on
	 * subsequent resubmissions (for lite restore). Should that fail us,
	 * and we try and submit the same tail again, force the context
	 * reload.
	 *
	 * If we need to return to a preempted context, we need to skip the
	 * lite-restore and force it to reload the RING_TAIL. Otherwise, the
	 * HW has a tendency to ignore us rewinding the TAIL to the end of
	 * an earlier request.
	 */
	GEM_BUG_ON(ce->lrc_reg_state[CTX_RING_TAIL] != rq->ring->tail);
	prev = rq->ring->tail;
	tail = intel_ring_set_tail(rq->ring, rq->tail);
	if (unlikely(intel_ring_direction(rq->ring, tail, prev) <= 0))
		desc |= CTX_DESC_FORCE_RESTORE;
	ce->lrc_reg_state[CTX_RING_TAIL] = tail;
	rq->tail = rq->wa_tail;

	/*
	 * Make sure the context image is complete before we submit it to HW.
	 *
	 * Ostensibly, writes (including the WCB) should be flushed prior to
	 * an uncached write such as our mmio register access, the empirical
	 * evidence (esp. on Braswell) suggests that the WC write into memory
	 * may not be visible to the HW prior to the completion of the UC
	 * register write and that we may begin execution from the context
	 * before its image is complete leading to invalid PD chasing.
	 */
	wmb();

	ce->lrc.desc &= ~CTX_DESC_FORCE_RESTORE;
	return desc;
}

static void write_desc(struct intel_engine_execlists *execlists, u64 desc, u32 port)
{
	if (execlists->ctrl_reg) {
		writel(lower_32_bits(desc), execlists->submit_reg + port * 2);
		writel(upper_32_bits(desc), execlists->submit_reg + port * 2 + 1);
	} else {
		writel(upper_32_bits(desc), execlists->submit_reg);
		writel(lower_32_bits(desc), execlists->submit_reg);
	}
}

static __maybe_unused char *
dump_port(char *buf, int buflen, const char *prefix, struct i915_request *rq)
{
	if (!rq)
		return "";

	snprintf(buf, buflen, "%sccid:%x %llx:%lld%s prio %d",
		 prefix,
		 rq->context->lrc.ccid,
		 rq->fence.context, rq->fence.seqno,
		 __i915_request_is_complete(rq) ? "!" :
		 __i915_request_has_started(rq) ? "*" :
		 "",
		 rq_prio(rq));

	return buf;
}

static __maybe_unused noinline void
trace_ports(const struct intel_engine_execlists *execlists,
	    const char *msg,
	    struct i915_request * const *ports)
{
	const struct intel_engine_cs *engine =
		container_of(execlists, typeof(*engine), execlists);
	char __maybe_unused p0[40], p1[40];

	if (!ports[0])
		return;

	ENGINE_TRACE(engine, "%s { %s%s }\n", msg,
		     dump_port(p0, sizeof(p0), "", ports[0]),
		     dump_port(p1, sizeof(p1), ", ", ports[1]));
}

static bool
reset_in_progress(const struct intel_engine_cs *engine)
{
	return unlikely(!__tasklet_is_enabled(&engine->sched_engine->tasklet));
}

static __maybe_unused noinline bool
assert_pending_valid(const struct intel_engine_execlists *execlists,
		     const char *msg)
{
	struct intel_engine_cs *engine =
		container_of(execlists, typeof(*engine), execlists);
	struct i915_request * const *port, *rq, *prev = NULL;
	struct intel_context *ce = NULL;
	u32 ccid = -1;

	trace_ports(execlists, msg, execlists->pending);

	/* We may be messing around with the lists during reset, lalala */
	if (reset_in_progress(engine))
		return true;

	if (!execlists->pending[0]) {
		GEM_TRACE_ERR("%s: Nothing pending for promotion!\n",
			      engine->name);
		return false;
	}

	if (execlists->pending[execlists_num_ports(execlists)]) {
		GEM_TRACE_ERR("%s: Excess pending[%d] for promotion!\n",
			      engine->name, execlists_num_ports(execlists));
		return false;
	}

	for (port = execlists->pending; (rq = *port); port++) {
		unsigned long flags;
		bool ok = true;

		GEM_BUG_ON(!kref_read(&rq->fence.refcount));
		GEM_BUG_ON(!i915_request_is_active(rq));

		if (ce == rq->context) {
			GEM_TRACE_ERR("%s: Dup context:%llx in pending[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			return false;
		}
		ce = rq->context;

		if (ccid == ce->lrc.ccid) {
			GEM_TRACE_ERR("%s: Dup ccid:%x context:%llx in pending[%zd]\n",
				      engine->name,
				      ccid, ce->timeline->fence_context,
				      port - execlists->pending);
			return false;
		}
		ccid = ce->lrc.ccid;

		/*
		 * Sentinels are supposed to be the last request so they flush
		 * the current execution off the HW. Check that they are the only
		 * request in the pending submission.
		 *
		 * NB: Due to the async nature of preempt-to-busy and request
		 * cancellation we need to handle the case where request
		 * becomes a sentinel in parallel to CSB processing.
		 */
		if (prev && i915_request_has_sentinel(prev) &&
		    !READ_ONCE(prev->fence.error)) {
			GEM_TRACE_ERR("%s: context:%llx after sentinel in pending[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			return false;
		}
		prev = rq;

		/*
		 * We want virtual requests to only be in the first slot so
		 * that they are never stuck behind a hog and can be immediately
		 * transferred onto the next idle engine.
		 */
		if (rq->execution_mask != engine->mask &&
		    port != execlists->pending) {
			GEM_TRACE_ERR("%s: virtual engine:%llx not in prime position[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			return false;
		}

		/* Hold tightly onto the lock to prevent concurrent retires! */
		if (!spin_trylock_irqsave(&rq->lock, flags))
			continue;

		if (__i915_request_is_complete(rq))
			goto unlock;

		if (i915_active_is_idle(&ce->active) &&
		    !intel_context_is_barrier(ce)) {
			GEM_TRACE_ERR("%s: Inactive context:%llx in pending[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			ok = false;
			goto unlock;
		}

		if (!i915_vma_is_pinned(ce->state)) {
			GEM_TRACE_ERR("%s: Unpinned context:%llx in pending[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			ok = false;
			goto unlock;
		}

		if (!i915_vma_is_pinned(ce->ring->vma)) {
			GEM_TRACE_ERR("%s: Unpinned ring:%llx in pending[%zd]\n",
				      engine->name,
				      ce->timeline->fence_context,
				      port - execlists->pending);
			ok = false;
			goto unlock;
		}

unlock:
		spin_unlock_irqrestore(&rq->lock, flags);
		if (!ok)
			return false;
	}

	return ce;
}

static void execlists_submit_ports(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists *execlists = &engine->execlists;
	unsigned int n;

	GEM_BUG_ON(!assert_pending_valid(execlists, "submit"));

	/*
	 * We can skip acquiring intel_runtime_pm_get() here as it was taken
	 * on our behalf by the request (see i915_gem_mark_busy()) and it will
	 * not be relinquished until the device is idle (see
	 * i915_gem_idle_work_handler()). As a precaution, we make sure
	 * that all ELSP are drained i.e. we have processed the CSB,
	 * before allowing ourselves to idle and calling intel_runtime_pm_put().
	 */
	GEM_BUG_ON(!intel_engine_pm_is_awake(engine));

	/*
	 * ELSQ note: the submit queue is not cleared after being submitted
	 * to the HW so we need to make sure we always clean it up. This is
	 * currently ensured by the fact that we always write the same number
	 * of elsq entries, keep this in mind before changing the loop below.
	 */
	for (n = execlists_num_ports(execlists); n--; ) {
		struct i915_request *rq = execlists->pending[n];

		write_desc(execlists,
			   rq ? execlists_update_context(rq) : 0,
			   n);
	}

	/* we need to manually load the submit queue */
	if (execlists->ctrl_reg)
		writel(EL_CTRL_LOAD, execlists->ctrl_reg);
}

static bool ctx_single_port_submission(const struct intel_context *ce)
{
	return (IS_ENABLED(CONFIG_DRM_I915_GVT) &&
		intel_context_force_single_submission(ce));
}

static bool can_merge_ctx(const struct intel_context *prev,
			  const struct intel_context *next)
{
	if (prev != next)
		return false;

	if (ctx_single_port_submission(prev))
		return false;

	return true;
}

static unsigned long i915_request_flags(const struct i915_request *rq)
{
	return READ_ONCE(rq->fence.flags);
}

static bool can_merge_rq(const struct i915_request *prev,
			 const struct i915_request *next)
{
	GEM_BUG_ON(prev == next);
	GEM_BUG_ON(!assert_priority_queue(prev, next));

	/*
	 * We do not submit known completed requests. Therefore if the next
	 * request is already completed, we can pretend to merge it in
	 * with the previous context (and we will skip updating the ELSP
	 * and tracking). Thus hopefully keeping the ELSP full with active
	 * contexts, despite the best efforts of preempt-to-busy to confuse
	 * us.
	 */
	if (__i915_request_is_complete(next))
		return true;

	if (unlikely((i915_request_flags(prev) | i915_request_flags(next)) &
		     (BIT(I915_FENCE_FLAG_NOPREEMPT) |
		      BIT(I915_FENCE_FLAG_SENTINEL))))
		return false;

	if (!can_merge_ctx(prev->context, next->context))
		return false;

	GEM_BUG_ON(i915_seqno_passed(prev->fence.seqno, next->fence.seqno));
	return true;
}

static bool virtual_matches(const struct virtual_engine *ve,
			    const struct i915_request *rq,
			    const struct intel_engine_cs *engine)
{
	const struct intel_engine_cs *inflight;

	if (!rq)
		return false;

	if (!(rq->execution_mask & engine->mask)) /* We peeked too soon! */
		return false;

	/*
	 * We track when the HW has completed saving the context image
	 * (i.e. when we have seen the final CS event switching out of
	 * the context) and must not overwrite the context image before
	 * then. This restricts us to only using the active engine
	 * while the previous virtualized request is inflight (so
	 * we reuse the register offsets). This is a very small
	 * hystersis on the greedy seelction algorithm.
	 */
	inflight = intel_context_inflight(&ve->context);
	if (inflight && inflight != engine)
		return false;

	return true;
}

static struct virtual_engine *
first_virtual_engine(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists *el = &engine->execlists;
	struct rb_node *rb = rb_first_cached(&el->virtual);

	while (rb) {
		struct virtual_engine *ve =
			rb_entry(rb, typeof(*ve), nodes[engine->id].rb);
		struct i915_request *rq = READ_ONCE(ve->request);

		/* lazily cleanup after another engine handled rq */
		if (!rq || !virtual_matches(ve, rq, engine)) {
			rb_erase_cached(rb, &el->virtual);
			RB_CLEAR_NODE(rb);
			rb = rb_first_cached(&el->virtual);
			continue;
		}

		return ve;
	}

	return NULL;
}

static void virtual_xfer_context(struct virtual_engine *ve,
				 struct intel_engine_cs *engine)
{
	unsigned int n;

	if (likely(engine == ve->siblings[0]))
		return;

	GEM_BUG_ON(READ_ONCE(ve->context.inflight));
	if (!intel_engine_has_relative_mmio(engine))
		lrc_update_offsets(&ve->context, engine);

	/*
	 * Move the bound engine to the top of the list for
	 * future execution. We then kick this tasklet first
	 * before checking others, so that we preferentially
	 * reuse this set of bound registers.
	 */
	for (n = 1; n < ve->num_siblings; n++) {
		if (ve->siblings[n] == engine) {
			swap(ve->siblings[n], ve->siblings[0]);
			break;
		}
	}
}

static void defer_request(struct i915_request *rq, struct list_head * const pl)
{
	LIST_HEAD(list);

	/*
	 * We want to move the interrupted request to the back of
	 * the round-robin list (i.e. its priority level), but
	 * in doing so, we must then move all requests that were in
	 * flight and were waiting for the interrupted request to
	 * be run after it again.
	 */
	do {
		struct i915_dependency *p;

		GEM_BUG_ON(i915_request_is_active(rq));
		list_move_tail(&rq->sched.link, pl);

		for_each_waiter(p, rq) {
			struct i915_request *w =
				container_of(p->waiter, typeof(*w), sched);

			if (p->flags & I915_DEPENDENCY_WEAK)
				continue;

			/* Leave semaphores spinning on the other engines */
			if (w->engine != rq->engine)
				continue;

			/* No waiter should start before its signaler */
			GEM_BUG_ON(i915_request_has_initial_breadcrumb(w) &&
				   __i915_request_has_started(w) &&
				   !__i915_request_is_complete(rq));

			if (!i915_request_is_ready(w))
				continue;

			if (rq_prio(w) < rq_prio(rq))
				continue;

			GEM_BUG_ON(rq_prio(w) > rq_prio(rq));
			GEM_BUG_ON(i915_request_is_active(w));
			list_move_tail(&w->sched.link, &list);
		}

		rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
	} while (rq);
}

static void defer_active(struct intel_engine_cs *engine)
{
	struct i915_request *rq;

	rq = __unwind_incomplete_requests(engine);
	if (!rq)
		return;

	defer_request(rq, i915_sched_lookup_priolist(engine->sched_engine,
						     rq_prio(rq)));
}

static bool
timeslice_yield(const struct intel_engine_execlists *el,
		const struct i915_request *rq)
{
	/*
	 * Once bitten, forever smitten!
	 *
	 * If the active context ever busy-waited on a semaphore,
	 * it will be treated as a hog until the end of its timeslice (i.e.
	 * until it is scheduled out and replaced by a new submission,
	 * possibly even its own lite-restore). The HW only sends an interrupt
	 * on the first miss, and we do know if that semaphore has been
	 * signaled, or even if it is now stuck on another semaphore. Play
	 * safe, yield if it might be stuck -- it will be given a fresh
	 * timeslice in the near future.
	 */
	return rq->context->lrc.ccid == READ_ONCE(el->yield);
}

static bool needs_timeslice(const struct intel_engine_cs *engine,
			    const struct i915_request *rq)
{
	if (!intel_engine_has_timeslices(engine))
		return false;

	/* If not currently active, or about to switch, wait for next event */
	if (!rq || __i915_request_is_complete(rq))
		return false;

	/* We do not need to start the timeslice until after the ACK */
	if (READ_ONCE(engine->execlists.pending[0]))
		return false;

	/* If ELSP[1] is occupied, always check to see if worth slicing */
	if (!list_is_last_rcu(&rq->sched.link,
			      &engine->sched_engine->requests)) {
		ENGINE_TRACE(engine, "timeslice required for second inflight context\n");
		return true;
	}

	/* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */
	if (!i915_sched_engine_is_empty(engine->sched_engine)) {
		ENGINE_TRACE(engine, "timeslice required for queue\n");
		return true;
	}

	if (!RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root)) {
		ENGINE_TRACE(engine, "timeslice required for virtual\n");
		return true;
	}

	return false;
}

static bool
timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq)
{
	const struct intel_engine_execlists *el = &engine->execlists;

	if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq))
		return false;

	if (!needs_timeslice(engine, rq))
		return false;

	return timer_expired(&el->timer) || timeslice_yield(el, rq);
}

static unsigned long timeslice(const struct intel_engine_cs *engine)
{
	return READ_ONCE(engine->props.timeslice_duration_ms);
}

static void start_timeslice(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists *el = &engine->execlists;
	unsigned long duration;

	/* Disable the timer if there is nothing to switch to */
	duration = 0;
	if (needs_timeslice(engine, *el->active)) {
		/* Avoid continually prolonging an active timeslice */
		if (timer_active(&el->timer)) {
			/*
			 * If we just submitted a new ELSP after an old
			 * context, that context may have already consumed
			 * its timeslice, so recheck.
			 */
			if (!timer_pending(&el->timer))
				tasklet_hi_schedule(&engine->sched_engine->tasklet);
			return;
		}

		duration = timeslice(engine);
	}

	set_timer_ms(&el->timer, duration);
}

static void record_preemption(struct intel_engine_execlists *execlists)
{
	(void)I915_SELFTEST_ONLY(execlists->preempt_hang.count++);
}

static unsigned long active_preempt_timeout(struct intel_engine_cs *engine,
					    const struct i915_request *rq)
{
	if (!rq)
		return 0;

	/* Force a fast reset for terminated contexts (ignoring sysfs!) */
	if (unlikely(intel_context_is_banned(rq->context) || bad_request(rq)))
		return 1;

	return READ_ONCE(engine->props.preempt_timeout_ms);
}

static void set_preempt_timeout(struct intel_engine_cs *engine,
				const struct i915_request *rq)
{
	if (!intel_engine_has_preempt_reset(engine))
		return;

	set_timer_ms(&engine->execlists.preempt,
		     active_preempt_timeout(engine, rq));
}

static bool completed(const struct i915_request *rq)
{
	if (i915_request_has_sentinel(rq))
		return false;

	return __i915_request_is_complete(rq);
}

static void execlists_dequeue(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	struct i915_sched_engine * const sched_engine = engine->sched_engine;
	struct i915_request **port = execlists->pending;
	struct i915_request ** const last_port = port + execlists->port_mask;
	struct i915_request *last, * const *active;
	struct virtual_engine *ve;
	struct rb_node *rb;
	bool submit = false;

	/*
	 * Hardware submission is through 2 ports. Conceptually each port
	 * has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
	 * static for a context, and unique to each, so we only execute
	 * requests belonging to a single context from each ring. RING_HEAD
	 * is maintained by the CS in the context image, it marks the place
	 * where it got up to last time, and through RING_TAIL we tell the CS
	 * where we want to execute up to this time.
	 *
	 * In this list the requests are in order of execution. Consecutive
	 * requests from the same context are adjacent in the ringbuffer. We
	 * can combine these requests into a single RING_TAIL update:
	 *
	 *              RING_HEAD...req1...req2
	 *                                    ^- RING_TAIL
	 * since to execute req2 the CS must first execute req1.
	 *
	 * Our goal then is to point each port to the end of a consecutive
	 * sequence of requests as being the most optimal (fewest wake ups
	 * and context switches) submission.
	 */

	spin_lock(&sched_engine->lock);

	/*
	 * If the queue is higher priority than the last
	 * request in the currently active context, submit afresh.
	 * We will resubmit again afterwards in case we need to split
	 * the active context to interject the preemption request,
	 * i.e. we will retrigger preemption following the ack in case
	 * of trouble.
	 *
	 */
	active = execlists->active;
	while ((last = *active) && completed(last))
		active++;

	if (last) {
		if (need_preempt(engine, last)) {
			ENGINE_TRACE(engine,
				     "preempting last=%llx:%lld, prio=%d, hint=%d\n",
				     last->fence.context,
				     last->fence.seqno,
				     last->sched.attr.priority,
				     sched_engine->queue_priority_hint);
			record_preemption(execlists);

			/*
			 * Don't let the RING_HEAD advance past the breadcrumb
			 * as we unwind (and until we resubmit) so that we do
			 * not accidentally tell it to go backwards.
			 */
			ring_set_paused(engine, 1);

			/*
			 * Note that we have not stopped the GPU at this point,
			 * so we are unwinding the incomplete requests as they
			 * remain inflight and so by the time we do complete
			 * the preemption, some of the unwound requests may
			 * complete!
			 */
			__unwind_incomplete_requests(engine);

			last = NULL;
		} else if (timeslice_expired(engine, last)) {
			ENGINE_TRACE(engine,
				     "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n",
				     yesno(timer_expired(&execlists->timer)),
				     last->fence.context, last->fence.seqno,
				     rq_prio(last),
				     sched_engine->queue_priority_hint,
				     yesno(timeslice_yield(execlists, last)));

			/*
			 * Consume this timeslice; ensure we start a new one.
			 *
			 * The timeslice expired, and we will unwind the
			 * running contexts and recompute the next ELSP.
			 * If that submit will be the same pair of contexts
			 * (due to dependency ordering), we will skip the
			 * submission. If we don't cancel the timer now,
			 * we will see that the timer has expired and
			 * reschedule the tasklet; continually until the
			 * next context switch or other preeemption event.
			 *
			 * Since we have decided to reschedule based on
			 * consumption of this timeslice, if we submit the
			 * same context again, grant it a full timeslice.
			 */
			cancel_timer(&execlists->timer);
			ring_set_paused(engine, 1);
			defer_active(engine);

			/*
			 * Unlike for preemption, if we rewind and continue
			 * executing the same context as previously active,
			 * the order of execution will remain the same and
			 * the tail will only advance. We do not need to
			 * force a full context restore, as a lite-restore
			 * is sufficient to resample the monotonic TAIL.
			 *
			 * If we switch to any other context, similarly we
			 * will not rewind TAIL of current context, and
			 * normal save/restore will preserve state and allow
			 * us to later continue executing the same request.
			 */
			last = NULL;
		} else {
			/*
			 * Otherwise if we already have a request pending
			 * for execution after the current one, we can
			 * just wait until the next CS event before
			 * queuing more. In either case we will force a
			 * lite-restore preemption event, but if we wait
			 * we hopefully coalesce several updates into a single
			 * submission.
			 */
			if (active[1]) {
				/*
				 * Even if ELSP[1] is occupied and not worthy
				 * of timeslices, our queue might be.
				 */
				spin_unlock(&sched_engine->lock);
				return;
			}
		}
	}

	/* XXX virtual is always taking precedence */
	while ((ve = first_virtual_engine(engine))) {
		struct i915_request *rq;

		spin_lock(&ve->base.sched_engine->lock);

		rq = ve->request;
		if (unlikely(!virtual_matches(ve, rq, engine)))
			goto unlock; /* lost the race to a sibling */

		GEM_BUG_ON(rq->engine != &ve->base);
		GEM_BUG_ON(rq->context != &ve->context);

		if (unlikely(rq_prio(rq) < queue_prio(sched_engine))) {
			spin_unlock(&ve->base.sched_engine->lock);
			break;
		}

		if (last && !can_merge_rq(last, rq)) {
			spin_unlock(&ve->base.sched_engine->lock);
			spin_unlock(&engine->sched_engine->lock);
			return; /* leave this for another sibling */
		}

		ENGINE_TRACE(engine,
			     "virtual rq=%llx:%lld%s, new engine? %s\n",
			     rq->fence.context,
			     rq->fence.seqno,
			     __i915_request_is_complete(rq) ? "!" :
			     __i915_request_has_started(rq) ? "*" :
			     "",
			     yesno(engine != ve->siblings[0]));

		WRITE_ONCE(ve->request, NULL);
		WRITE_ONCE(ve->base.sched_engine->queue_priority_hint, INT_MIN);

		rb = &ve->nodes[engine->id].rb;
		rb_erase_cached(rb, &execlists->virtual);
		RB_CLEAR_NODE(rb);

		GEM_BUG_ON(!(rq->execution_mask & engine->mask));
		WRITE_ONCE(rq->engine, engine);

		if (__i915_request_submit(rq)) {
			/*
			 * Only after we confirm that we will submit
			 * this request (i.e. it has not already
			 * completed), do we want to update the context.
			 *
			 * This serves two purposes. It avoids
			 * unnecessary work if we are resubmitting an
			 * already completed request after timeslicing.
			 * But more importantly, it prevents us altering
			 * ve->siblings[] on an idle context, where
			 * we may be using ve->siblings[] in
			 * virtual_context_enter / virtual_context_exit.
			 */
			virtual_xfer_context(ve, engine);
			GEM_BUG_ON(ve->siblings[0] != engine);

			submit = true;
			last = rq;
		}

		i915_request_put(rq);
unlock:
		spin_unlock(&ve->base.sched_engine->lock);

		/*
		 * Hmm, we have a bunch of virtual engine requests,
		 * but the first one was already completed (thanks
		 * preempt-to-busy!). Keep looking at the veng queue
		 * until we have no more relevant requests (i.e.
		 * the normal submit queue has higher priority).
		 */
		if (submit)
			break;
	}

	while ((rb = rb_first_cached(&sched_engine->queue))) {
		struct i915_priolist *p = to_priolist(rb);
		struct i915_request *rq, *rn;

		priolist_for_each_request_consume(rq, rn, p) {
			bool merge = true;

			/*
			 * Can we combine this request with the current port?
			 * It has to be the same context/ringbuffer and not
			 * have any exceptions (e.g. GVT saying never to
			 * combine contexts).
			 *
			 * If we can combine the requests, we can execute both
			 * by updating the RING_TAIL to point to the end of the
			 * second request, and so we never need to tell the
			 * hardware about the first.
			 */
			if (last && !can_merge_rq(last, rq)) {
				/*
				 * If we are on the second port and cannot
				 * combine this request with the last, then we
				 * are done.
				 */
				if (port == last_port)
					goto done;

				/*
				 * We must not populate both ELSP[] with the
				 * same LRCA, i.e. we must submit 2 different
				 * contexts if we submit 2 ELSP.
				 */
				if (last->context == rq->context)
					goto done;

				if (i915_request_has_sentinel(last))
					goto done;

				/*
				 * We avoid submitting virtual requests into
				 * the secondary ports so that we can migrate
				 * the request immediately to another engine
				 * rather than wait for the primary request.
				 */
				if (rq->execution_mask != engine->mask)
					goto done;

				/*
				 * If GVT overrides us we only ever submit
				 * port[0], leaving port[1] empty. Note that we
				 * also have to be careful that we don't queue
				 * the same context (even though a different
				 * request) to the second port.
				 */
				if (ctx_single_port_submission(last->context) ||
				    ctx_single_port_submission(rq->context))
					goto done;

				merge = false;
			}

			if (__i915_request_submit(rq)) {
				if (!merge) {
					*port++ = i915_request_get(last);
					last = NULL;
				}

				GEM_BUG_ON(last &&
					   !can_merge_ctx(last->context,
							  rq->context));
				GEM_BUG_ON(last &&
					   i915_seqno_passed(last->fence.seqno,
							     rq->fence.seqno));

				submit = true;
				last = rq;
			}
		}

		rb_erase_cached(&p->node, &sched_engine->queue);
		i915_priolist_free(p);
	}
done:
	*port++ = i915_request_get(last);

	/*
	 * Here be a bit of magic! Or sleight-of-hand, whichever you prefer.
	 *
	 * We choose the priority hint such that if we add a request of greater
	 * priority than this, we kick the submission tasklet to decide on
	 * the right order of submitting the requests to hardware. We must
	 * also be prepared to reorder requests as they are in-flight on the
	 * HW. We derive the priority hint then as the first "hole" in
	 * the HW submission ports and if there are no available slots,
	 * the priority of the lowest executing request, i.e. last.
	 *
	 * When we do receive a higher priority request ready to run from the
	 * user, see queue_request(), the priority hint is bumped to that
	 * request triggering preemption on the next dequeue (or subsequent
	 * interrupt for secondary ports).
	 */
	sched_engine->queue_priority_hint = queue_prio(sched_engine);
	i915_sched_engine_reset_on_empty(sched_engine);
	spin_unlock(&sched_engine->lock);

	/*
	 * We can skip poking the HW if we ended up with exactly the same set
	 * of requests as currently running, e.g. trying to timeslice a pair
	 * of ordered contexts.
	 */
	if (submit &&
	    memcmp(active,
		   execlists->pending,
		   (port - execlists->pending) * sizeof(*port))) {
		*port = NULL;
		while (port-- != execlists->pending)
			execlists_schedule_in(*port, port - execlists->pending);

		WRITE_ONCE(execlists->yield, -1);
		set_preempt_timeout(engine, *active);
		execlists_submit_ports(engine);
	} else {
		ring_set_paused(engine, 0);
		while (port-- != execlists->pending)
			i915_request_put(*port);
		*execlists->pending = NULL;
	}
}

static void execlists_dequeue_irq(struct intel_engine_cs *engine)
{
	local_irq_disable(); /* Suspend interrupts across request submission */
	execlists_dequeue(engine);
	local_irq_enable(); /* flush irq_work (e.g. breadcrumb enabling) */
}

static void clear_ports(struct i915_request **ports, int count)
{
	memset_p((void **)ports, NULL, count);
}

static void
copy_ports(struct i915_request **dst, struct i915_request **src, int count)
{
	/* A memcpy_p() would be very useful here! */
	while (count--)
		WRITE_ONCE(*dst++, *src++); /* avoid write tearing */
}

static struct i915_request **
cancel_port_requests(struct intel_engine_execlists * const execlists,
		     struct i915_request **inactive)
{
	struct i915_request * const *port;

	for (port = execlists->pending; *port; port++)
		*inactive++ = *port;
	clear_ports(execlists->pending, ARRAY_SIZE(execlists->pending));

	/* Mark the end of active before we overwrite *active */
	for (port = xchg(&execlists->active, execlists->pending); *port; port++)
		*inactive++ = *port;
	clear_ports(execlists->inflight, ARRAY_SIZE(execlists->inflight));

	smp_wmb(); /* complete the seqlock for execlists_active() */
	WRITE_ONCE(execlists->active, execlists->inflight);

	/* Having cancelled all outstanding process_csb(), stop their timers */
	GEM_BUG_ON(execlists->pending[0]);
	cancel_timer(&execlists->timer);
	cancel_timer(&execlists->preempt);

	return inactive;
}

static void invalidate_csb_entries(const u64 *first, const u64 *last)
{
	clflush((void *)first);
	clflush((void *)last);
}

/*
 * Starting with Gen12, the status has a new format:
 *
 *     bit  0:     switched to new queue
 *     bit  1:     reserved
 *     bit  2:     semaphore wait mode (poll or signal), only valid when
 *                 switch detail is set to "wait on semaphore"
 *     bits 3-5:   engine class
 *     bits 6-11:  engine instance
 *     bits 12-14: reserved
 *     bits 15-25: sw context id of the lrc the GT switched to
 *     bits 26-31: sw counter of the lrc the GT switched to
 *     bits 32-35: context switch detail
 *                  - 0: ctx complete
 *                  - 1: wait on sync flip
 *                  - 2: wait on vblank
 *                  - 3: wait on scanline
 *                  - 4: wait on semaphore
 *                  - 5: context preempted (not on SEMAPHORE_WAIT or
 *                       WAIT_FOR_EVENT)
 *     bit  36:    reserved
 *     bits 37-43: wait detail (for switch detail 1 to 4)
 *     bits 44-46: reserved
 *     bits 47-57: sw context id of the lrc the GT switched away from
 *     bits 58-63: sw counter of the lrc the GT switched away from
 */
static bool gen12_csb_parse(const u64 csb)
{
	bool ctx_away_valid = GEN12_CSB_CTX_VALID(upper_32_bits(csb));
	bool new_queue =
		lower_32_bits(csb) & GEN12_CTX_STATUS_SWITCHED_TO_NEW_QUEUE;

	/*
	 * The context switch detail is not guaranteed to be 5 when a preemption
	 * occurs, so we can't just check for that. The check below works for
	 * all the cases we care about, including preemptions of WAIT
	 * instructions and lite-restore. Preempt-to-idle via the CTRL register
	 * would require some extra handling, but we don't support that.
	 */
	if (!ctx_away_valid || new_queue) {
		GEM_BUG_ON(!GEN12_CSB_CTX_VALID(lower_32_bits(csb)));
		return true;
	}

	/*
	 * switch detail = 5 is covered by the case above and we do not expect a
	 * context switch on an unsuccessful wait instruction since we always
	 * use polling mode.
	 */
	GEM_BUG_ON(GEN12_CTX_SWITCH_DETAIL(upper_32_bits(csb)));
	return false;
}

static bool gen8_csb_parse(const u64 csb)
{
	return csb & (GEN8_CTX_STATUS_IDLE_ACTIVE | GEN8_CTX_STATUS_PREEMPTED);
}

static noinline u64
wa_csb_read(const struct intel_engine_cs *engine, u64 * const csb)
{
	u64 entry;

	/*
	 * Reading from the HWSP has one particular advantage: we can detect
	 * a stale entry. Since the write into HWSP is broken, we have no reason
	 * to trust the HW at all, the mmio entry may equally be unordered, so
	 * we prefer the path that is self-checking and as a last resort,
	 * return the mmio value.
	 *
	 * tgl,dg1:HSDES#22011327657
	 */
	preempt_disable();
	if (wait_for_atomic_us((entry = READ_ONCE(*csb)) != -1, 10)) {
		int idx = csb - engine->execlists.csb_status;
		int status;

		status = GEN8_EXECLISTS_STATUS_BUF;
		if (idx >= 6) {
			status = GEN11_EXECLISTS_STATUS_BUF2;
			idx -= 6;
		}
		status += sizeof(u64) * idx;

		entry = intel_uncore_read64(engine->uncore,
					    _MMIO(engine->mmio_base + status));
	}
	preempt_enable();

	return entry;
}

static u64 csb_read(const struct intel_engine_cs *engine, u64 * const csb)
{
	u64 entry = READ_ONCE(*csb);

	/*
	 * Unfortunately, the GPU does not always serialise its write
	 * of the CSB entries before its write of the CSB pointer, at least
	 * from the perspective of the CPU, using what is known as a Global
	 * Observation Point. We may read a new CSB tail pointer, but then
	 * read the stale CSB entries, causing us to misinterpret the
	 * context-switch events, and eventually declare the GPU hung.
	 *
	 * icl:HSDES#1806554093
	 * tgl:HSDES#22011248461
	 */
	if (unlikely(entry == -1))
		entry = wa_csb_read(engine, csb);

	/* Consume this entry so that we can spot its future reuse. */
	WRITE_ONCE(*csb, -1);

	/* ELSP is an implicit wmb() before the GPU wraps and overwrites csb */
	return entry;
}

static void new_timeslice(struct intel_engine_execlists *el)
{
	/* By cancelling, we will start afresh in start_timeslice() */
	cancel_timer(&el->timer);
}

static struct i915_request **
process_csb(struct intel_engine_cs *engine, struct i915_request **inactive)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	u64 * const buf = execlists->csb_status;
	const u8 num_entries = execlists->csb_size;
	struct i915_request **prev;
	u8 head, tail;

	/*
	 * As we modify our execlists state tracking we require exclusive
	 * access. Either we are inside the tasklet, or the tasklet is disabled
	 * and we assume that is only inside the reset paths and so serialised.
	 */
	GEM_BUG_ON(!tasklet_is_locked(&engine->sched_engine->tasklet) &&
		   !reset_in_progress(engine));

	/*
	 * Note that csb_write, csb_status may be either in HWSP or mmio.
	 * When reading from the csb_write mmio register, we have to be
	 * careful to only use the GEN8_CSB_WRITE_PTR portion, which is
	 * the low 4bits. As it happens we know the next 4bits are always
	 * zero and so we can simply masked off the low u8 of the register
	 * and treat it identically to reading from the HWSP (without having
	 * to use explicit shifting and masking, and probably bifurcating
	 * the code to handle the legacy mmio read).
	 */
	head = execlists->csb_head;
	tail = READ_ONCE(*execlists->csb_write);
	if (unlikely(head == tail))
		return inactive;

	/*
	 * We will consume all events from HW, or at least pretend to.
	 *
	 * The sequence of events from the HW is deterministic, and derived
	 * from our writes to the ELSP, with a smidgen of variability for
	 * the arrival of the asynchronous requests wrt to the inflight
	 * execution. If the HW sends an event that does not correspond with
	 * the one we are expecting, we have to abandon all hope as we lose
	 * all tracking of what the engine is actually executing. We will
	 * only detect we are out of sequence with the HW when we get an
	 * 'impossible' event because we have already drained our own
	 * preemption/promotion queue. If this occurs, we know that we likely
	 * lost track of execution earlier and must unwind and restart, the
	 * simplest way is by stop processing the event queue and force the
	 * engine to reset.
	 */
	execlists->csb_head = tail;
	ENGINE_TRACE(engine, "cs-irq head=%d, tail=%d\n", head, tail);

	/*
	 * Hopefully paired with a wmb() in HW!
	 *
	 * We must complete the read of the write pointer before any reads
	 * from the CSB, so that we do not see stale values. Without an rmb
	 * (lfence) the HW may speculatively perform the CSB[] reads *before*
	 * we perform the READ_ONCE(*csb_write).
	 */
	rmb();

	/* Remember who was last running under the timer */
	prev = inactive;
	*prev = NULL;

	do {
		bool promote;
		u64 csb;

		if (++head == num_entries)
			head = 0;

		/*
		 * We are flying near dragons again.
		 *
		 * We hold a reference to the request in execlist_port[]
		 * but no more than that. We are operating in softirq
		 * context and so cannot hold any mutex or sleep. That
		 * prevents us stopping the requests we are processing
		 * in port[] from being retired simultaneously (the
		 * breadcrumb will be complete before we see the
		 * context-switch). As we only hold the reference to the
		 * request, any pointer chasing underneath the request
		 * is subject to a potential use-after-free. Thus we
		 * store all of the bookkeeping within port[] as
		 * required, and avoid using unguarded pointers beneath
		 * request itself. The same applies to the atomic
		 * status notifier.
		 */

		csb = csb_read(engine, buf + head);
		ENGINE_TRACE(engine, "csb[%d]: status=0x%08x:0x%08x\n",
			     head, upper_32_bits(csb), lower_32_bits(csb));

		if (GRAPHICS_VER(engine->i915) >= 12)
			promote = gen12_csb_parse(csb);
		else
			promote = gen8_csb_parse(csb);
		if (promote) {
			struct i915_request * const *old = execlists->active;

			if (GEM_WARN_ON(!*execlists->pending)) {
				execlists->error_interrupt |= ERROR_CSB;
				break;
			}

			ring_set_paused(engine, 0);

			/* Point active to the new ELSP; prevent overwriting */
			WRITE_ONCE(execlists->active, execlists->pending);
			smp_wmb(); /* notify execlists_active() */

			/* cancel old inflight, prepare for switch */
			trace_ports(execlists, "preempted", old);
			while (*old)
				*inactive++ = *old++;

			/* switch pending to inflight */
			GEM_BUG_ON(!assert_pending_valid(execlists, "promote"));
			copy_ports(execlists->inflight,
				   execlists->pending,
				   execlists_num_ports(execlists));
			smp_wmb(); /* complete the seqlock */
			WRITE_ONCE(execlists->active, execlists->inflight);

			/* XXX Magic delay for tgl */
			ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

			WRITE_ONCE(execlists->pending[0], NULL);
		} else {
			if (GEM_WARN_ON(!*execlists->active)) {
				execlists->error_interrupt |= ERROR_CSB;
				break;
			}

			/* port0 completed, advanced to port1 */
			trace_ports(execlists, "completed", execlists->active);

			/*
			 * We rely on the hardware being strongly
			 * ordered, that the breadcrumb write is
			 * coherent (visible from the CPU) before the
			 * user interrupt is processed. One might assume
			 * that the breadcrumb write being before the
			 * user interrupt and the CS event for the context
			 * switch would therefore be before the CS event
			 * itself...
			 */
			if (GEM_SHOW_DEBUG() &&
			    !__i915_request_is_complete(*execlists->active)) {
				struct i915_request *rq = *execlists->active;
				const u32 *regs __maybe_unused =
					rq->context->lrc_reg_state;

				ENGINE_TRACE(engine,
					     "context completed before request!\n");
				ENGINE_TRACE(engine,
					     "ring:{start:0x%08x, head:%04x, tail:%04x, ctl:%08x, mode:%08x}\n",
					     ENGINE_READ(engine, RING_START),
					     ENGINE_READ(engine, RING_HEAD) & HEAD_ADDR,
					     ENGINE_READ(engine, RING_TAIL) & TAIL_ADDR,
					     ENGINE_READ(engine, RING_CTL),
					     ENGINE_READ(engine, RING_MI_MODE));
				ENGINE_TRACE(engine,
					     "rq:{start:%08x, head:%04x, tail:%04x, seqno:%llx:%d, hwsp:%d}, ",
					     i915_ggtt_offset(rq->ring->vma),
					     rq->head, rq->tail,
					     rq->fence.context,
					     lower_32_bits(rq->fence.seqno),
					     hwsp_seqno(rq));
				ENGINE_TRACE(engine,
					     "ctx:{start:%08x, head:%04x, tail:%04x}, ",
					     regs[CTX_RING_START],
					     regs[CTX_RING_HEAD],
					     regs[CTX_RING_TAIL]);
			}

			*inactive++ = *execlists->active++;

			GEM_BUG_ON(execlists->active - execlists->inflight >
				   execlists_num_ports(execlists));
		}
	} while (head != tail);

	/*
	 * Gen11 has proven to fail wrt global observation point between
	 * entry and tail update, failing on the ordering and thus
	 * we see an old entry in the context status buffer.
	 *
	 * Forcibly evict out entries for the next gpu csb update,
	 * to increase the odds that we get a fresh entries with non
	 * working hardware. The cost for doing so comes out mostly with
	 * the wash as hardware, working or not, will need to do the
	 * invalidation before.
	 */
	invalidate_csb_entries(&buf[0], &buf[num_entries - 1]);

	/*
	 * We assume that any event reflects a change in context flow
	 * and merits a fresh timeslice. We reinstall the timer after
	 * inspecting the queue to see if we need to resumbit.
	 */
	if (*prev != *execlists->active) /* elide lite-restores */
		new_timeslice(execlists);

	return inactive;
}

static void post_process_csb(struct i915_request **port,
			     struct i915_request **last)
{
	while (port != last)
		execlists_schedule_out(*port++);
}

static void __execlists_hold(struct i915_request *rq)
{
	LIST_HEAD(list);

	do {
		struct i915_dependency *p;

		if (i915_request_is_active(rq))
			__i915_request_unsubmit(rq);

		clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
		list_move_tail(&rq->sched.link,
			       &rq->engine->sched_engine->hold);
		i915_request_set_hold(rq);
		RQ_TRACE(rq, "on hold\n");

		for_each_waiter(p, rq) {
			struct i915_request *w =
				container_of(p->waiter, typeof(*w), sched);

			if (p->flags & I915_DEPENDENCY_WEAK)
				continue;

			/* Leave semaphores spinning on the other engines */
			if (w->engine != rq->engine)
				continue;

			if (!i915_request_is_ready(w))
				continue;

			if (__i915_request_is_complete(w))
				continue;

			if (i915_request_on_hold(w))
				continue;

			list_move_tail(&w->sched.link, &list);
		}

		rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
	} while (rq);
}

static bool execlists_hold(struct intel_engine_cs *engine,
			   struct i915_request *rq)
{
	if (i915_request_on_hold(rq))
		return false;

	spin_lock_irq(&engine->sched_engine->lock);

	if (__i915_request_is_complete(rq)) { /* too late! */
		rq = NULL;
		goto unlock;
	}

	/*
	 * Transfer this request onto the hold queue to prevent it
	 * being resumbitted to HW (and potentially completed) before we have
	 * released it. Since we may have already submitted following
	 * requests, we need to remove those as well.
	 */
	GEM_BUG_ON(i915_request_on_hold(rq));
	GEM_BUG_ON(rq->engine != engine);
	__execlists_hold(rq);
	GEM_BUG_ON(list_empty(&engine->sched_engine->hold));

unlock:
	spin_unlock_irq(&engine->sched_engine->lock);
	return rq;
}

static bool hold_request(const struct i915_request *rq)
{
	struct i915_dependency *p;
	bool result = false;

	/*
	 * If one of our ancestors is on hold, we must also be on hold,
	 * otherwise we will bypass it and execute before it.
	 */
	rcu_read_lock();
	for_each_signaler(p, rq) {
		const struct i915_request *s =
			container_of(p->signaler, typeof(*s), sched);

		if (s->engine != rq->engine)
			continue;

		result = i915_request_on_hold(s);
		if (result)
			break;
	}
	rcu_read_unlock();

	return result;
}

static void __execlists_unhold(struct i915_request *rq)
{
	LIST_HEAD(list);

	do {
		struct i915_dependency *p;

		RQ_TRACE(rq, "hold release\n");

		GEM_BUG_ON(!i915_request_on_hold(rq));
		GEM_BUG_ON(!i915_sw_fence_signaled(&rq->submit));

		i915_request_clear_hold(rq);
		list_move_tail(&rq->sched.link,
			       i915_sched_lookup_priolist(rq->engine->sched_engine,
							  rq_prio(rq)));
		set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);

		/* Also release any children on this engine that are ready */
		for_each_waiter(p, rq) {
			struct i915_request *w =
				container_of(p->waiter, typeof(*w), sched);

			if (p->flags & I915_DEPENDENCY_WEAK)
				continue;

			/* Propagate any change in error status */
			if (rq->fence.error)
				i915_request_set_error_once(w, rq->fence.error);

			if (w->engine != rq->engine)
				continue;

			if (!i915_request_on_hold(w))
				continue;

			/* Check that no other parents are also on hold */
			if (hold_request(w))
				continue;

			list_move_tail(&w->sched.link, &list);
		}

		rq = list_first_entry_or_null(&list, typeof(*rq), sched.link);
	} while (rq);
}

static void execlists_unhold(struct intel_engine_cs *engine,
			     struct i915_request *rq)
{
	spin_lock_irq(&engine->sched_engine->lock);

	/*
	 * Move this request back to the priority queue, and all of its
	 * children and grandchildren that were suspended along with it.
	 */
	__execlists_unhold(rq);

	if (rq_prio(rq) > engine->sched_engine->queue_priority_hint) {
		engine->sched_engine->queue_priority_hint = rq_prio(rq);
		tasklet_hi_schedule(&engine->sched_engine->tasklet);
	}

	spin_unlock_irq(&engine->sched_engine->lock);
}

struct execlists_capture {
	struct work_struct work;
	struct i915_request *rq;
	struct i915_gpu_coredump *error;
};

static void execlists_capture_work(struct work_struct *work)
{
	struct execlists_capture *cap = container_of(work, typeof(*cap), work);
	const gfp_t gfp = GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
	struct intel_engine_cs *engine = cap->rq->engine;
	struct intel_gt_coredump *gt = cap->error->gt;
	struct intel_engine_capture_vma *vma;

	/* Compress all the objects attached to the request, slow! */
	vma = intel_engine_coredump_add_request(gt->engine, cap->rq, gfp);
	if (vma) {
		struct i915_vma_compress *compress =
			i915_vma_capture_prepare(gt);

		intel_engine_coredump_add_vma(gt->engine, vma, compress);
		i915_vma_capture_finish(gt, compress);
	}

	gt->simulated = gt->engine->simulated;
	cap->error->simulated = gt->simulated;

	/* Publish the error state, and announce it to the world */
	i915_error_state_store(cap->error);
	i915_gpu_coredump_put(cap->error);

	/* Return this request and all that depend upon it for signaling */
	execlists_unhold(engine, cap->rq);
	i915_request_put(cap->rq);

	kfree(cap);
}

static struct execlists_capture *capture_regs(struct intel_engine_cs *engine)
{
	const gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
	struct execlists_capture *cap;

	cap = kmalloc(sizeof(*cap), gfp);
	if (!cap)
		return NULL;

	cap->error = i915_gpu_coredump_alloc(engine->i915, gfp);
	if (!cap->error)
		goto err_cap;

	cap->error->gt = intel_gt_coredump_alloc(engine->gt, gfp);
	if (!cap->error->gt)
		goto err_gpu;

	cap->error->gt->engine = intel_engine_coredump_alloc(engine, gfp);
	if (!cap->error->gt->engine)
		goto err_gt;

	cap->error->gt->engine->hung = true;

	return cap;

err_gt:
	kfree(cap->error->gt);
err_gpu:
	kfree(cap->error);
err_cap:
	kfree(cap);
	return NULL;
}

static struct i915_request *
active_context(struct intel_engine_cs *engine, u32 ccid)
{
	const struct intel_engine_execlists * const el = &engine->execlists;
	struct i915_request * const *port, *rq;

	/*
	 * Use the most recent result from process_csb(), but just in case
	 * we trigger an error (via interrupt) before the first CS event has
	 * been written, peek at the next submission.
	 */

	for (port = el->active; (rq = *port); port++) {
		if (rq->context->lrc.ccid == ccid) {
			ENGINE_TRACE(engine,
				     "ccid:%x found at active:%zd\n",
				     ccid, port - el->active);
			return rq;
		}
	}

	for (port = el->pending; (rq = *port); port++) {
		if (rq->context->lrc.ccid == ccid) {
			ENGINE_TRACE(engine,
				     "ccid:%x found at pending:%zd\n",
				     ccid, port - el->pending);
			return rq;
		}
	}

	ENGINE_TRACE(engine, "ccid:%x not found\n", ccid);
	return NULL;
}

static u32 active_ccid(struct intel_engine_cs *engine)
{
	return ENGINE_READ_FW(engine, RING_EXECLIST_STATUS_HI);
}

static void execlists_capture(struct intel_engine_cs *engine)
{
	struct execlists_capture *cap;

	if (!IS_ENABLED(CONFIG_DRM_I915_CAPTURE_ERROR))
		return;

	/*
	 * We need to _quickly_ capture the engine state before we reset.
	 * We are inside an atomic section (softirq) here and we are delaying
	 * the forced preemption event.
	 */
	cap = capture_regs(engine);
	if (!cap)
		return;

	spin_lock_irq(&engine->sched_engine->lock);
	cap->rq = active_context(engine, active_ccid(engine));
	if (cap->rq) {
		cap->rq = active_request(cap->rq->context->timeline, cap->rq);
		cap->rq = i915_request_get_rcu(cap->rq);
	}
	spin_unlock_irq(&engine->sched_engine->lock);
	if (!cap->rq)
		goto err_free;

	/*
	 * Remove the request from the execlists queue, and take ownership
	 * of the request. We pass it to our worker who will _slowly_ compress
	 * all the pages the _user_ requested for debugging their batch, after
	 * which we return it to the queue for signaling.
	 *
	 * By removing them from the execlists queue, we also remove the
	 * requests from being processed by __unwind_incomplete_requests()
	 * during the intel_engine_reset(), and so they will *not* be replayed
	 * afterwards.
	 *
	 * Note that because we have not yet reset the engine at this point,
	 * it is possible for the request that we have identified as being
	 * guilty, did in fact complete and we will then hit an arbitration
	 * point allowing the outstanding preemption to succeed. The likelihood
	 * of that is very low (as capturing of the engine registers should be
	 * fast enough to run inside an irq-off atomic section!), so we will
	 * simply hold that request accountable for being non-preemptible
	 * long enough to force the reset.
	 */
	if (!execlists_hold(engine, cap->rq))
		goto err_rq;

	INIT_WORK(&cap->work, execlists_capture_work);
	schedule_work(&cap->work);
	return;

err_rq:
	i915_request_put(cap->rq);
err_free:
	i915_gpu_coredump_put(cap->error);
	kfree(cap);
}

static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
{
	const unsigned int bit = I915_RESET_ENGINE + engine->id;
	unsigned long *lock = &engine->gt->reset.flags;

	if (!intel_has_reset_engine(engine->gt))
		return;

	if (test_and_set_bit(bit, lock))
		return;

	ENGINE_TRACE(engine, "reset for %s\n", msg);

	/* Mark this tasklet as disabled to avoid waiting for it to complete */
	tasklet_disable_nosync(&engine->sched_engine->tasklet);

	ring_set_paused(engine, 1); /* Freeze the current request in place */
	execlists_capture(engine);
	intel_engine_reset(engine, msg);

	tasklet_enable(&engine->sched_engine->tasklet);
	clear_and_wake_up_bit(bit, lock);
}

static bool preempt_timeout(const struct intel_engine_cs *const engine)
{
	const struct timer_list *t = &engine->execlists.preempt;

	if (!CONFIG_DRM_I915_PREEMPT_TIMEOUT)
		return false;

	if (!timer_expired(t))
		return false;

	return engine->execlists.pending[0];
}

/*
 * Check the unread Context Status Buffers and manage the submission of new
 * contexts to the ELSP accordingly.
 */
static void execlists_submission_tasklet(struct tasklet_struct *t)
{
	struct i915_sched_engine *sched_engine =
		from_tasklet(sched_engine, t, tasklet);
	struct intel_engine_cs * const engine = sched_engine->private_data;
	struct i915_request *post[2 * EXECLIST_MAX_PORTS];
	struct i915_request **inactive;

	rcu_read_lock();
	inactive = process_csb(engine, post);
	GEM_BUG_ON(inactive - post > ARRAY_SIZE(post));

	if (unlikely(preempt_timeout(engine))) {
		cancel_timer(&engine->execlists.preempt);
		engine->execlists.error_interrupt |= ERROR_PREEMPT;
	}

	if (unlikely(READ_ONCE(engine->execlists.error_interrupt))) {
		const char *msg;

		/* Generate the error message in priority wrt to the user! */
		if (engine->execlists.error_interrupt & GENMASK(15, 0))
			msg = "CS error"; /* thrown by a user payload */
		else if (engine->execlists.error_interrupt & ERROR_CSB)
			msg = "invalid CSB event";
		else if (engine->execlists.error_interrupt & ERROR_PREEMPT)
			msg = "preemption time out";
		else
			msg = "internal error";

		engine->execlists.error_interrupt = 0;
		execlists_reset(engine, msg);
	}

	if (!engine->execlists.pending[0]) {
		execlists_dequeue_irq(engine);
		start_timeslice(engine);
	}

	post_process_csb(post, inactive);
	rcu_read_unlock();
}

static void execlists_irq_handler(struct intel_engine_cs *engine, u16 iir)
{
	bool tasklet = false;

	if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
		u32 eir;

		/* Upper 16b are the enabling mask, rsvd for internal errors */
		eir = ENGINE_READ(engine, RING_EIR) & GENMASK(15, 0);
		ENGINE_TRACE(engine, "CS error: %x\n", eir);

		/* Disable the error interrupt until after the reset */
		if (likely(eir)) {
			ENGINE_WRITE(engine, RING_EMR, ~0u);
			ENGINE_WRITE(engine, RING_EIR, eir);
			WRITE_ONCE(engine->execlists.error_interrupt, eir);
			tasklet = true;
		}
	}

	if (iir & GT_WAIT_SEMAPHORE_INTERRUPT) {
		WRITE_ONCE(engine->execlists.yield,
			   ENGINE_READ_FW(engine, RING_EXECLIST_STATUS_HI));
		ENGINE_TRACE(engine, "semaphore yield: %08x\n",
			     engine->execlists.yield);
		if (del_timer(&engine->execlists.timer))
			tasklet = true;
	}

	if (iir & GT_CONTEXT_SWITCH_INTERRUPT)
		tasklet = true;

	if (iir & GT_RENDER_USER_INTERRUPT)
		intel_engine_signal_breadcrumbs(engine);

	if (tasklet)
		tasklet_hi_schedule(&engine->sched_engine->tasklet);
}

static void __execlists_kick(struct intel_engine_execlists *execlists)
{
	struct intel_engine_cs *engine =
		container_of(execlists, typeof(*engine), execlists);

	/* Kick the tasklet for some interrupt coalescing and reset handling */
	tasklet_hi_schedule(&engine->sched_engine->tasklet);
}

#define execlists_kick(t, member) \
	__execlists_kick(container_of(t, struct intel_engine_execlists, member))

static void execlists_timeslice(struct timer_list *timer)
{
	execlists_kick(timer, timer);
}

static void execlists_preempt(struct timer_list *timer)
{
	execlists_kick(timer, preempt);
}

static void queue_request(struct intel_engine_cs *engine,
			  struct i915_request *rq)
{
	GEM_BUG_ON(!list_empty(&rq->sched.link));
	list_add_tail(&rq->sched.link,
		      i915_sched_lookup_priolist(engine->sched_engine,
						 rq_prio(rq)));
	set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
}

static bool submit_queue(struct intel_engine_cs *engine,
			 const struct i915_request *rq)
{
	struct i915_sched_engine *sched_engine = engine->sched_engine;

	if (rq_prio(rq) <= sched_engine->queue_priority_hint)
		return false;

	sched_engine->queue_priority_hint = rq_prio(rq);
	return true;
}

static bool ancestor_on_hold(const struct intel_engine_cs *engine,
			     const struct i915_request *rq)
{
	GEM_BUG_ON(i915_request_on_hold(rq));
	return !list_empty(&engine->sched_engine->hold) && hold_request(rq);
}

static void execlists_submit_request(struct i915_request *request)
{
	struct intel_engine_cs *engine = request->engine;
	unsigned long flags;

	/* Will be called from irq-context when using foreign fences. */
	spin_lock_irqsave(&engine->sched_engine->lock, flags);

	if (unlikely(ancestor_on_hold(engine, request))) {
		RQ_TRACE(request, "ancestor on hold\n");
		list_add_tail(&request->sched.link,
			      &engine->sched_engine->hold);
		i915_request_set_hold(request);
	} else {
		queue_request(engine, request);

		GEM_BUG_ON(i915_sched_engine_is_empty(engine->sched_engine));
		GEM_BUG_ON(list_empty(&request->sched.link));

		if (submit_queue(engine, request))
			__execlists_kick(&engine->execlists);
	}

	spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
}

static int
__execlists_context_pre_pin(struct intel_context *ce,
			    struct intel_engine_cs *engine,
			    struct i915_gem_ww_ctx *ww, void **vaddr)
{
	int err;

	err = lrc_pre_pin(ce, engine, ww, vaddr);
	if (err)
		return err;

	if (!__test_and_set_bit(CONTEXT_INIT_BIT, &ce->flags)) {
		lrc_init_state(ce, engine, *vaddr);

		 __i915_gem_object_flush_map(ce->state->obj, 0, engine->context_size);
	}

	return 0;
}

static int execlists_context_pre_pin(struct intel_context *ce,
				     struct i915_gem_ww_ctx *ww,
				     void **vaddr)
{
	return __execlists_context_pre_pin(ce, ce->engine, ww, vaddr);
}

static int execlists_context_pin(struct intel_context *ce, void *vaddr)
{
	return lrc_pin(ce, ce->engine, vaddr);
}

static int execlists_context_alloc(struct intel_context *ce)
{
	return lrc_alloc(ce, ce->engine);
}

static const struct intel_context_ops execlists_context_ops = {
	.flags = COPS_HAS_INFLIGHT,

	.alloc = execlists_context_alloc,

	.pre_pin = execlists_context_pre_pin,
	.pin = execlists_context_pin,
	.unpin = lrc_unpin,
	.post_unpin = lrc_post_unpin,

	.enter = intel_context_enter_engine,
	.exit = intel_context_exit_engine,

	.reset = lrc_reset,
	.destroy = lrc_destroy,
};

static int emit_pdps(struct i915_request *rq)
{
	const struct intel_engine_cs * const engine = rq->engine;
	struct i915_ppgtt * const ppgtt = i915_vm_to_ppgtt(rq->context->vm);
	int err, i;
	u32 *cs;

	GEM_BUG_ON(intel_vgpu_active(rq->engine->i915));

	/*
	 * Beware ye of the dragons, this sequence is magic!
	 *
	 * Small changes to this sequence can cause anything from
	 * GPU hangs to forcewake errors and machine lockups!
	 */

	cs = intel_ring_begin(rq, 2);
	if (IS_ERR(cs))
		return PTR_ERR(cs);

	*cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
	*cs++ = MI_NOOP;
	intel_ring_advance(rq, cs);

	/* Flush any residual operations from the context load */
	err = engine->emit_flush(rq, EMIT_FLUSH);
	if (err)
		return err;

	/* Magic required to prevent forcewake errors! */
	err = engine->emit_flush(rq, EMIT_INVALIDATE);
	if (err)
		return err;

	cs = intel_ring_begin(rq, 4 * GEN8_3LVL_PDPES + 2);
	if (IS_ERR(cs))
		return PTR_ERR(cs);

	/* Ensure the LRI have landed before we invalidate & continue */
	*cs++ = MI_LOAD_REGISTER_IMM(2 * GEN8_3LVL_PDPES) | MI_LRI_FORCE_POSTED;
	for (i = GEN8_3LVL_PDPES; i--; ) {
		const dma_addr_t pd_daddr = i915_page_dir_dma_addr(ppgtt, i);
		u32 base = engine->mmio_base;

		*cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_UDW(base, i));
		*cs++ = upper_32_bits(pd_daddr);
		*cs++ = i915_mmio_reg_offset(GEN8_RING_PDP_LDW(base, i));
		*cs++ = lower_32_bits(pd_daddr);
	}
	*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
	intel_ring_advance(rq, cs);

	intel_ring_advance(rq, cs);

	return 0;
}

static int execlists_request_alloc(struct i915_request *request)
{
	int ret;

	GEM_BUG_ON(!intel_context_is_pinned(request->context));

	/*
	 * Flush enough space to reduce the likelihood of waiting after
	 * we start building the request - in which case we will just
	 * have to repeat work.
	 */
	request->reserved_space += EXECLISTS_REQUEST_SIZE;

	/*
	 * Note that after this point, we have committed to using
	 * this request as it is being used to both track the
	 * state of engine initialisation and liveness of the
	 * golden renderstate above. Think twice before you try
	 * to cancel/unwind this request now.
	 */

	if (!i915_vm_is_4lvl(request->context->vm)) {
		ret = emit_pdps(request);
		if (ret)
			return ret;
	}

	/* Unconditionally invalidate GPU caches and TLBs. */
	ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
	if (ret)
		return ret;

	request->reserved_space -= EXECLISTS_REQUEST_SIZE;
	return 0;
}

static void reset_csb_pointers(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	const unsigned int reset_value = execlists->csb_size - 1;

	ring_set_paused(engine, 0);

	/*
	 * Sometimes Icelake forgets to reset its pointers on a GPU reset.
	 * Bludgeon them with a mmio update to be sure.
	 */
	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
		     0xffff << 16 | reset_value << 8 | reset_value);
	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

	/*
	 * After a reset, the HW starts writing into CSB entry [0]. We
	 * therefore have to set our HEAD pointer back one entry so that
	 * the *first* entry we check is entry 0. To complicate this further,
	 * as we don't wait for the first interrupt after reset, we have to
	 * fake the HW write to point back to the last entry so that our
	 * inline comparison of our cached head position against the last HW
	 * write works even before the first interrupt.
	 */
	execlists->csb_head = reset_value;
	WRITE_ONCE(*execlists->csb_write, reset_value);
	wmb(); /* Make sure this is visible to HW (paranoia?) */

	/* Check that the GPU does indeed update the CSB entries! */
	memset(execlists->csb_status, -1, (reset_value + 1) * sizeof(u64));
	invalidate_csb_entries(&execlists->csb_status[0],
			       &execlists->csb_status[reset_value]);

	/* Once more for luck and our trusty paranoia */
	ENGINE_WRITE(engine, RING_CONTEXT_STATUS_PTR,
		     0xffff << 16 | reset_value << 8 | reset_value);
	ENGINE_POSTING_READ(engine, RING_CONTEXT_STATUS_PTR);

	GEM_BUG_ON(READ_ONCE(*execlists->csb_write) != reset_value);
}

static void sanitize_hwsp(struct intel_engine_cs *engine)
{
	struct intel_timeline *tl;

	list_for_each_entry(tl, &engine->status_page.timelines, engine_link)
		intel_timeline_reset_seqno(tl);
}

static void execlists_sanitize(struct intel_engine_cs *engine)
{
	GEM_BUG_ON(execlists_active(&engine->execlists));

	/*
	 * Poison residual state on resume, in case the suspend didn't!
	 *
	 * We have to assume that across suspend/resume (or other loss
	 * of control) that the contents of our pinned buffers has been
	 * lost, replaced by garbage. Since this doesn't always happen,
	 * let's poison such state so that we more quickly spot when
	 * we falsely assume it has been preserved.
	 */
	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
		memset(engine->status_page.addr, POISON_INUSE, PAGE_SIZE);

	reset_csb_pointers(engine);

	/*
	 * The kernel_context HWSP is stored in the status_page. As above,
	 * that may be lost on resume/initialisation, and so we need to
	 * reset the value in the HWSP.
	 */
	sanitize_hwsp(engine);

	/* And scrub the dirty cachelines for the HWSP */
	clflush_cache_range(engine->status_page.addr, PAGE_SIZE);
}

static void enable_error_interrupt(struct intel_engine_cs *engine)
{
	u32 status;

	engine->execlists.error_interrupt = 0;
	ENGINE_WRITE(engine, RING_EMR, ~0u);
	ENGINE_WRITE(engine, RING_EIR, ~0u); /* clear all existing errors */

	status = ENGINE_READ(engine, RING_ESR);
	if (unlikely(status)) {
		drm_err(&engine->i915->drm,
			"engine '%s' resumed still in error: %08x\n",
			engine->name, status);
		__intel_gt_reset(engine->gt, engine->mask);
	}

	/*
	 * On current gen8+, we have 2 signals to play with
	 *
	 * - I915_ERROR_INSTUCTION (bit 0)
	 *
	 *    Generate an error if the command parser encounters an invalid
	 *    instruction
	 *
	 *    This is a fatal error.
	 *
	 * - CP_PRIV (bit 2)
	 *
	 *    Generate an error on privilege violation (where the CP replaces
	 *    the instruction with a no-op). This also fires for writes into
	 *    read-only scratch pages.
	 *
	 *    This is a non-fatal error, parsing continues.
	 *
	 * * there are a few others defined for odd HW that we do not use
	 *
	 * Since CP_PRIV fires for cases where we have chosen to ignore the
	 * error (as the HW is validating and suppressing the mistakes), we
	 * only unmask the instruction error bit.
	 */
	ENGINE_WRITE(engine, RING_EMR, ~I915_ERROR_INSTRUCTION);
}

static void enable_execlists(struct intel_engine_cs *engine)
{
	u32 mode;

	assert_forcewakes_active(engine->uncore, FORCEWAKE_ALL);

	intel_engine_set_hwsp_writemask(engine, ~0u); /* HWSTAM */

	if (GRAPHICS_VER(engine->i915) >= 11)
		mode = _MASKED_BIT_ENABLE(GEN11_GFX_DISABLE_LEGACY_MODE);
	else
		mode = _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE);
	ENGINE_WRITE_FW(engine, RING_MODE_GEN7, mode);

	ENGINE_WRITE_FW(engine, RING_MI_MODE, _MASKED_BIT_DISABLE(STOP_RING));

	ENGINE_WRITE_FW(engine,
			RING_HWS_PGA,
			i915_ggtt_offset(engine->status_page.vma));
	ENGINE_POSTING_READ(engine, RING_HWS_PGA);

	enable_error_interrupt(engine);
}

static int execlists_resume(struct intel_engine_cs *engine)
{
	intel_mocs_init_engine(engine);
	intel_breadcrumbs_reset(engine->breadcrumbs);

	enable_execlists(engine);

	return 0;
}

static void execlists_reset_prepare(struct intel_engine_cs *engine)
{
	ENGINE_TRACE(engine, "depth<-%d\n",
		     atomic_read(&engine->sched_engine->tasklet.count));

	/*
	 * Prevent request submission to the hardware until we have
	 * completed the reset in i915_gem_reset_finish(). If a request
	 * is completed by one engine, it may then queue a request
	 * to a second via its execlists->tasklet *just* as we are
	 * calling engine->resume() and also writing the ELSP.
	 * Turning off the execlists->tasklet until the reset is over
	 * prevents the race.
	 */
	__tasklet_disable_sync_once(&engine->sched_engine->tasklet);
	GEM_BUG_ON(!reset_in_progress(engine));

	/*
	 * We stop engines, otherwise we might get failed reset and a
	 * dead gpu (on elk). Also as modern gpu as kbl can suffer
	 * from system hang if batchbuffer is progressing when
	 * the reset is issued, regardless of READY_TO_RESET ack.
	 * Thus assume it is best to stop engines on all gens
	 * where we have a gpu reset.
	 *
	 * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
	 *
	 * FIXME: Wa for more modern gens needs to be validated
	 */
	ring_set_paused(engine, 1);
	intel_engine_stop_cs(engine);

	engine->execlists.reset_ccid = active_ccid(engine);
}

static struct i915_request **
reset_csb(struct intel_engine_cs *engine, struct i915_request **inactive)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;

	mb(); /* paranoia: read the CSB pointers from after the reset */
	clflush(execlists->csb_write);
	mb();

	inactive = process_csb(engine, inactive); /* drain preemption events */

	/* Following the reset, we need to reload the CSB read/write pointers */
	reset_csb_pointers(engine);

	return inactive;
}

static void
execlists_reset_active(struct intel_engine_cs *engine, bool stalled)
{
	struct intel_context *ce;
	struct i915_request *rq;
	u32 head;

	/*
	 * Save the currently executing context, even if we completed
	 * its request, it was still running at the time of the
	 * reset and will have been clobbered.
	 */
	rq = active_context(engine, engine->execlists.reset_ccid);
	if (!rq)
		return;

	ce = rq->context;
	GEM_BUG_ON(!i915_vma_is_pinned(ce->state));

	if (__i915_request_is_complete(rq)) {
		/* Idle context; tidy up the ring so we can restart afresh */
		head = intel_ring_wrap(ce->ring, rq->tail);
		goto out_replay;
	}

	/* We still have requests in-flight; the engine should be active */
	GEM_BUG_ON(!intel_engine_pm_is_awake(engine));

	/* Context has requests still in-flight; it should not be idle! */
	GEM_BUG_ON(i915_active_is_idle(&ce->active));

	rq = active_request(ce->timeline, rq);
	head = intel_ring_wrap(ce->ring, rq->head);
	GEM_BUG_ON(head == ce->ring->tail);

	/*
	 * If this request hasn't started yet, e.g. it is waiting on a
	 * semaphore, we need to avoid skipping the request or else we
	 * break the signaling chain. However, if the context is corrupt
	 * the request will not restart and we will be stuck with a wedged
	 * device. It is quite often the case that if we issue a reset
	 * while the GPU is loading the context image, that the context
	 * image becomes corrupt.
	 *
	 * Otherwise, if we have not started yet, the request should replay
	 * perfectly and we do not need to flag the result as being erroneous.
	 */
	if (!__i915_request_has_started(rq))
		goto out_replay;

	/*
	 * If the request was innocent, we leave the request in the ELSP
	 * and will try to replay it on restarting. The context image may
	 * have been corrupted by the reset, in which case we may have
	 * to service a new GPU hang, but more likely we can continue on
	 * without impact.
	 *
	 * If the request was guilty, we presume the context is corrupt
	 * and have to at least restore the RING register in the context
	 * image back to the expected values to skip over the guilty request.
	 */
	__i915_request_reset(rq, stalled);

	/*
	 * We want a simple context + ring to execute the breadcrumb update.
	 * We cannot rely on the context being intact across the GPU hang,
	 * so clear it and rebuild just what we need for the breadcrumb.
	 * All pending requests for this context will be zapped, and any
	 * future request will be after userspace has had the opportunity
	 * to recreate its own state.
	 */
out_replay:
	ENGINE_TRACE(engine, "replay {head:%04x, tail:%04x}\n",
		     head, ce->ring->tail);
	lrc_reset_regs(ce, engine);
	ce->lrc.lrca = lrc_update_regs(ce, engine, head);
}

static void execlists_reset_csb(struct intel_engine_cs *engine, bool stalled)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	struct i915_request *post[2 * EXECLIST_MAX_PORTS];
	struct i915_request **inactive;

	rcu_read_lock();
	inactive = reset_csb(engine, post);

	execlists_reset_active(engine, true);

	inactive = cancel_port_requests(execlists, inactive);
	post_process_csb(post, inactive);
	rcu_read_unlock();
}

static void execlists_reset_rewind(struct intel_engine_cs *engine, bool stalled)
{
	unsigned long flags;

	ENGINE_TRACE(engine, "\n");

	/* Process the csb, find the guilty context and throw away */
	execlists_reset_csb(engine, stalled);

	/* Push back any incomplete requests for replay after the reset. */
	rcu_read_lock();
	spin_lock_irqsave(&engine->sched_engine->lock, flags);
	__unwind_incomplete_requests(engine);
	spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
	rcu_read_unlock();
}

static void nop_submission_tasklet(struct tasklet_struct *t)
{
	struct i915_sched_engine *sched_engine =
		from_tasklet(sched_engine, t, tasklet);
	struct intel_engine_cs * const engine = sched_engine->private_data;

	/* The driver is wedged; don't process any more events. */
	WRITE_ONCE(engine->sched_engine->queue_priority_hint, INT_MIN);
}

static void execlists_reset_cancel(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	struct i915_sched_engine * const sched_engine = engine->sched_engine;
	struct i915_request *rq, *rn;
	struct rb_node *rb;
	unsigned long flags;

	ENGINE_TRACE(engine, "\n");

	/*
	 * Before we call engine->cancel_requests(), we should have exclusive
	 * access to the submission state. This is arranged for us by the
	 * caller disabling the interrupt generation, the tasklet and other
	 * threads that may then access the same state, giving us a free hand
	 * to reset state. However, we still need to let lockdep be aware that
	 * we know this state may be accessed in hardirq context, so we
	 * disable the irq around this manipulation and we want to keep
	 * the spinlock focused on its duties and not accidentally conflate
	 * coverage to the submission's irq state. (Similarly, although we
	 * shouldn't need to disable irq around the manipulation of the
	 * submission's irq state, we also wish to remind ourselves that
	 * it is irq state.)
	 */
	execlists_reset_csb(engine, true);

	rcu_read_lock();
	spin_lock_irqsave(&engine->sched_engine->lock, flags);

	/* Mark all executing requests as skipped. */
	list_for_each_entry(rq, &engine->sched_engine->requests, sched.link)
		i915_request_put(i915_request_mark_eio(rq));
	intel_engine_signal_breadcrumbs(engine);

	/* Flush the queued requests to the timeline list (for retiring). */
	while ((rb = rb_first_cached(&sched_engine->queue))) {
		struct i915_priolist *p = to_priolist(rb);

		priolist_for_each_request_consume(rq, rn, p) {
			if (i915_request_mark_eio(rq)) {
				__i915_request_submit(rq);
				i915_request_put(rq);
			}
		}

		rb_erase_cached(&p->node, &sched_engine->queue);
		i915_priolist_free(p);
	}

	/* On-hold requests will be flushed to timeline upon their release */
	list_for_each_entry(rq, &sched_engine->hold, sched.link)
		i915_request_put(i915_request_mark_eio(rq));

	/* Cancel all attached virtual engines */
	while ((rb = rb_first_cached(&execlists->virtual))) {
		struct virtual_engine *ve =
			rb_entry(rb, typeof(*ve), nodes[engine->id].rb);

		rb_erase_cached(rb, &execlists->virtual);
		RB_CLEAR_NODE(rb);

		spin_lock(&ve->base.sched_engine->lock);
		rq = fetch_and_zero(&ve->request);
		if (rq) {
			if (i915_request_mark_eio(rq)) {
				rq->engine = engine;
				__i915_request_submit(rq);
				i915_request_put(rq);
			}
			i915_request_put(rq);

			ve->base.sched_engine->queue_priority_hint = INT_MIN;
		}
		spin_unlock(&ve->base.sched_engine->lock);
	}

	/* Remaining _unready_ requests will be nop'ed when submitted */

	sched_engine->queue_priority_hint = INT_MIN;
	sched_engine->queue = RB_ROOT_CACHED;

	GEM_BUG_ON(__tasklet_is_enabled(&engine->sched_engine->tasklet));
	engine->sched_engine->tasklet.callback = nop_submission_tasklet;

	spin_unlock_irqrestore(&engine->sched_engine->lock, flags);
	rcu_read_unlock();
}

static void execlists_reset_finish(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;

	/*
	 * After a GPU reset, we may have requests to replay. Do so now while
	 * we still have the forcewake to be sure that the GPU is not allowed
	 * to sleep before we restart and reload a context.
	 *
	 * If the GPU reset fails, the engine may still be alive with requests
	 * inflight. We expect those to complete, or for the device to be
	 * reset as the next level of recovery, and as a final resort we
	 * will declare the device wedged.
	 */
	GEM_BUG_ON(!reset_in_progress(engine));

	/* And kick in case we missed a new request submission. */
	if (__tasklet_enable(&engine->sched_engine->tasklet))
		__execlists_kick(execlists);

	ENGINE_TRACE(engine, "depth->%d\n",
		     atomic_read(&engine->sched_engine->tasklet.count));
}

static void gen8_logical_ring_enable_irq(struct intel_engine_cs *engine)
{
	ENGINE_WRITE(engine, RING_IMR,
		     ~(engine->irq_enable_mask | engine->irq_keep_mask));
	ENGINE_POSTING_READ(engine, RING_IMR);
}

static void gen8_logical_ring_disable_irq(struct intel_engine_cs *engine)
{
	ENGINE_WRITE(engine, RING_IMR, ~engine->irq_keep_mask);
}

static void execlists_park(struct intel_engine_cs *engine)
{
	cancel_timer(&engine->execlists.timer);
	cancel_timer(&engine->execlists.preempt);
}

static bool can_preempt(struct intel_engine_cs *engine)
{
	if (GRAPHICS_VER(engine->i915) > 8)
		return true;

	/* GPGPU on bdw requires extra w/a; not implemented */
	return engine->class != RENDER_CLASS;
}

static void kick_execlists(const struct i915_request *rq, int prio)
{
	struct intel_engine_cs *engine = rq->engine;
	struct i915_sched_engine *sched_engine = engine->sched_engine;
	const struct i915_request *inflight;

	/*
	 * We only need to kick the tasklet once for the high priority
	 * new context we add into the queue.
	 */
	if (prio <= sched_engine->queue_priority_hint)
		return;

	rcu_read_lock();

	/* Nothing currently active? We're overdue for a submission! */
	inflight = execlists_active(&engine->execlists);
	if (!inflight)
		goto unlock;

	/*
	 * If we are already the currently executing context, don't
	 * bother evaluating if we should preempt ourselves.
	 */
	if (inflight->context == rq->context)
		goto unlock;

	ENGINE_TRACE(engine,
		     "bumping queue-priority-hint:%d for rq:%llx:%lld, inflight:%llx:%lld prio %d\n",
		     prio,
		     rq->fence.context, rq->fence.seqno,
		     inflight->fence.context, inflight->fence.seqno,
		     inflight->sched.attr.priority);

	sched_engine->queue_priority_hint = prio;

	/*
	 * Allow preemption of low -> normal -> high, but we do
	 * not allow low priority tasks to preempt other low priority
	 * tasks under the impression that latency for low priority
	 * tasks does not matter (as much as background throughput),
	 * so kiss.
	 */
	if (prio >= max(I915_PRIORITY_NORMAL, rq_prio(inflight)))
		tasklet_hi_schedule(&sched_engine->tasklet);

unlock:
	rcu_read_unlock();
}

static void execlists_set_default_submission(struct intel_engine_cs *engine)
{
	engine->submit_request = execlists_submit_request;
	engine->sched_engine->schedule = i915_schedule;
	engine->sched_engine->kick_backend = kick_execlists;
	engine->sched_engine->tasklet.callback = execlists_submission_tasklet;
}

static void execlists_shutdown(struct intel_engine_cs *engine)
{
	/* Synchronise with residual timers and any softirq they raise */
	del_timer_sync(&engine->execlists.timer);
	del_timer_sync(&engine->execlists.preempt);
	tasklet_kill(&engine->sched_engine->tasklet);
}

static void execlists_release(struct intel_engine_cs *engine)
{
	engine->sanitize = NULL; /* no longer in control, nothing to sanitize */

	execlists_shutdown(engine);

	intel_engine_cleanup_common(engine);
	lrc_fini_wa_ctx(engine);
}

static void
logical_ring_default_vfuncs(struct intel_engine_cs *engine)
{
	/* Default vfuncs which can be overridden by each engine. */

	engine->resume = execlists_resume;

	engine->cops = &execlists_context_ops;
	engine->request_alloc = execlists_request_alloc;

	engine->reset.prepare = execlists_reset_prepare;
	engine->reset.rewind = execlists_reset_rewind;
	engine->reset.cancel = execlists_reset_cancel;
	engine->reset.finish = execlists_reset_finish;

	engine->park = execlists_park;
	engine->unpark = NULL;

	engine->emit_flush = gen8_emit_flush_xcs;
	engine->emit_init_breadcrumb = gen8_emit_init_breadcrumb;
	engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb_xcs;
	if (GRAPHICS_VER(engine->i915) >= 12) {
		engine->emit_fini_breadcrumb = gen12_emit_fini_breadcrumb_xcs;
		engine->emit_flush = gen12_emit_flush_xcs;
	}
	engine->set_default_submission = execlists_set_default_submission;

	if (GRAPHICS_VER(engine->i915) < 11) {
		engine->irq_enable = gen8_logical_ring_enable_irq;
		engine->irq_disable = gen8_logical_ring_disable_irq;
	} else {
		/*
		 * TODO: On Gen11 interrupt masks need to be clear
		 * to allow C6 entry. Keep interrupts enabled at
		 * and take the hit of generating extra interrupts
		 * until a more refined solution exists.
		 */
	}
	intel_engine_set_irq_handler(engine, execlists_irq_handler);

	engine->flags |= I915_ENGINE_SUPPORTS_STATS;
	if (!intel_vgpu_active(engine->i915)) {
		engine->flags |= I915_ENGINE_HAS_SEMAPHORES;
		if (can_preempt(engine)) {
			engine->flags |= I915_ENGINE_HAS_PREEMPTION;
			if (IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
				engine->flags |= I915_ENGINE_HAS_TIMESLICES;
		}
	}

	if (intel_engine_has_preemption(engine))
		engine->emit_bb_start = gen8_emit_bb_start;
	else
		engine->emit_bb_start = gen8_emit_bb_start_noarb;
}

static void logical_ring_default_irqs(struct intel_engine_cs *engine)
{
	unsigned int shift = 0;

	if (GRAPHICS_VER(engine->i915) < 11) {
		const u8 irq_shifts[] = {
			[RCS0]  = GEN8_RCS_IRQ_SHIFT,
			[BCS0]  = GEN8_BCS_IRQ_SHIFT,
			[VCS0]  = GEN8_VCS0_IRQ_SHIFT,
			[VCS1]  = GEN8_VCS1_IRQ_SHIFT,
			[VECS0] = GEN8_VECS_IRQ_SHIFT,
		};

		shift = irq_shifts[engine->id];
	}

	engine->irq_enable_mask = GT_RENDER_USER_INTERRUPT << shift;
	engine->irq_keep_mask = GT_CONTEXT_SWITCH_INTERRUPT << shift;
	engine->irq_keep_mask |= GT_CS_MASTER_ERROR_INTERRUPT << shift;
	engine->irq_keep_mask |= GT_WAIT_SEMAPHORE_INTERRUPT << shift;
}

static void rcs_submission_override(struct intel_engine_cs *engine)
{
	switch (GRAPHICS_VER(engine->i915)) {
	case 12:
		engine->emit_flush = gen12_emit_flush_rcs;
		engine->emit_fini_breadcrumb = gen12_emit_fini_breadcrumb_rcs;
		break;
	case 11:
		engine->emit_flush = gen11_emit_flush_rcs;
		engine->emit_fini_breadcrumb = gen11_emit_fini_breadcrumb_rcs;
		break;
	default:
		engine->emit_flush = gen8_emit_flush_rcs;
		engine->emit_fini_breadcrumb = gen8_emit_fini_breadcrumb_rcs;
		break;
	}
}

int intel_execlists_submission_setup(struct intel_engine_cs *engine)
{
	struct intel_engine_execlists * const execlists = &engine->execlists;
	struct drm_i915_private *i915 = engine->i915;
	struct intel_uncore *uncore = engine->uncore;
	u32 base = engine->mmio_base;

	tasklet_setup(&engine->sched_engine->tasklet, execlists_submission_tasklet);
	timer_setup(&engine->execlists.timer, execlists_timeslice, 0);
	timer_setup(&engine->execlists.preempt, execlists_preempt, 0);

	logical_ring_default_vfuncs(engine);
	logical_ring_default_irqs(engine);

	if (engine->class == RENDER_CLASS)
		rcs_submission_override(engine);

	lrc_init_wa_ctx(engine);

	if (HAS_LOGICAL_RING_ELSQ(i915)) {
		execlists->submit_reg = uncore->regs +
			i915_mmio_reg_offset(RING_EXECLIST_SQ_CONTENTS(base));
		execlists->ctrl_reg = uncore->regs +
			i915_mmio_reg_offset(RING_EXECLIST_CONTROL(base));
	} else {
		execlists->submit_reg = uncore->regs +
			i915_mmio_reg_offset(RING_ELSP(base));
	}

	execlists->csb_status =
		(u64 *)&engine->status_page.addr[I915_HWS_CSB_BUF0_INDEX];

	execlists->csb_write =
		&engine->status_page.addr[intel_hws_csb_write_index(i915)];

	if (GRAPHICS_VER(i915) < 11)
		execlists->csb_size = GEN8_CSB_ENTRIES;
	else
		execlists->csb_size = GEN11_CSB_ENTRIES;

	engine->context_tag = GENMASK(BITS_PER_LONG - 2, 0);
	if (GRAPHICS_VER(engine->i915) >= 11) {
		execlists->ccid |= engine->instance << (GEN11_ENGINE_INSTANCE_SHIFT - 32);
		execlists->ccid |= engine->class << (GEN11_ENGINE_CLASS_SHIFT - 32);
	}

	/* Finally, take ownership and responsibility for cleanup! */
	engine->sanitize = execlists_sanitize;
	engine->release = execlists_release;

	return 0;
}

static struct list_head *virtual_queue(struct virtual_engine *ve)
{
	return &ve->base.sched_engine->default_priolist.requests;
}

static void rcu_virtual_context_destroy(struct work_struct *wrk)
{
	struct virtual_engine *ve =
		container_of(wrk, typeof(*ve), rcu.work);
	unsigned int n;

	GEM_BUG_ON(ve->context.inflight);

	/* Preempt-to-busy may leave a stale request behind. */
	if (unlikely(ve->request)) {
		struct i915_request *old;

		spin_lock_irq(&ve->base.sched_engine->lock);

		old = fetch_and_zero(&ve->request);
		if (old) {
			GEM_BUG_ON(!__i915_request_is_complete(old));
			__i915_request_submit(old);
			i915_request_put(old);
		}

		spin_unlock_irq(&ve->base.sched_engine->lock);
	}

	/*
	 * Flush the tasklet in case it is still running on another core.
	 *
	 * This needs to be done before we remove ourselves from the siblings'
	 * rbtrees as in the case it is running in parallel, it may reinsert
	 * the rb_node into a sibling.
	 */
	tasklet_kill(&ve->base.sched_engine->tasklet);

	/* Decouple ourselves from the siblings, no more access allowed. */
	for (n = 0; n < ve->num_siblings; n++) {
		struct intel_engine_cs *sibling = ve->siblings[n];
		struct rb_node *node = &ve->nodes[sibling->id].rb;

		if (RB_EMPTY_NODE(node))
			continue;

		spin_lock_irq(&sibling->sched_engine->lock);

		/* Detachment is lazily performed in the sched_engine->tasklet */
		if (!RB_EMPTY_NODE(node))
			rb_erase_cached(node, &sibling->execlists.virtual);

		spin_unlock_irq(&sibling->sched_engine->lock);
	}
	GEM_BUG_ON(__tasklet_is_scheduled(&ve->base.sched_engine->tasklet));
	GEM_BUG_ON(!list_empty(virtual_queue(ve)));

	lrc_fini(&ve->context);
	intel_context_fini(&ve->context);

	if (ve->base.breadcrumbs)
		intel_breadcrumbs_free(ve->base.breadcrumbs);
	if (ve->base.sched_engine)
		i915_sched_engine_put(ve->base.sched_engine);
	intel_engine_free_request_pool(&ve->base);

	kfree(ve->bonds);
	kfree(ve);
}

static void virtual_context_destroy(struct kref *kref)
{
	struct virtual_engine *ve =
		container_of(kref, typeof(*ve), context.ref);

	GEM_BUG_ON(!list_empty(&ve->context.signals));

	/*
	 * When destroying the virtual engine, we have to be aware that
	 * it may still be in use from an hardirq/softirq context causing
	 * the resubmission of a completed request (background completion
	 * due to preempt-to-busy). Before we can free the engine, we need
	 * to flush the submission code and tasklets that are still potentially
	 * accessing the engine. Flushing the tasklets requires process context,
	 * and since we can guard the resubmit onto the engine with an RCU read
	 * lock, we can delegate the free of the engine to an RCU worker.
	 */
	INIT_RCU_WORK(&ve->rcu, rcu_virtual_context_destroy);
	queue_rcu_work(system_wq, &ve->rcu);
}

static void virtual_engine_initial_hint(struct virtual_engine *ve)
{
	int swp;

	/*
	 * Pick a random sibling on starting to help spread the load around.
	 *
	 * New contexts are typically created with exactly the same order
	 * of siblings, and often started in batches. Due to the way we iterate
	 * the array of sibling when submitting requests, sibling[0] is
	 * prioritised for dequeuing. If we make sure that sibling[0] is fairly
	 * randomised across the system, we also help spread the load by the
	 * first engine we inspect being different each time.
	 *
	 * NB This does not force us to execute on this engine, it will just
	 * typically be the first we inspect for submission.
	 */
	swp = prandom_u32_max(ve->num_siblings);
	if (swp)
		swap(ve->siblings[swp], ve->siblings[0]);
}

static int virtual_context_alloc(struct intel_context *ce)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

	return lrc_alloc(ce, ve->siblings[0]);
}

static int virtual_context_pre_pin(struct intel_context *ce,
				   struct i915_gem_ww_ctx *ww,
				   void **vaddr)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

	 /* Note: we must use a real engine class for setting up reg state */
	return __execlists_context_pre_pin(ce, ve->siblings[0], ww, vaddr);
}

static int virtual_context_pin(struct intel_context *ce, void *vaddr)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);

	return lrc_pin(ce, ve->siblings[0], vaddr);
}

static void virtual_context_enter(struct intel_context *ce)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
	unsigned int n;

	for (n = 0; n < ve->num_siblings; n++)
		intel_engine_pm_get(ve->siblings[n]);

	intel_timeline_enter(ce->timeline);
}

static void virtual_context_exit(struct intel_context *ce)
{
	struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
	unsigned int n;

	intel_timeline_exit(ce->timeline);

	for (n = 0; n < ve->num_siblings; n++)
		intel_engine_pm_put(ve->siblings[n]);
}

static const struct intel_context_ops virtual_context_ops = {
	.flags = COPS_HAS_INFLIGHT,

	.alloc = virtual_context_alloc,

	.pre_pin = virtual_context_pre_pin,
	.pin = virtual_context_pin,
	.unpin = lrc_unpin,
	.post_unpin = lrc_post_unpin,

	.enter = virtual_context_enter,
	.exit = virtual_context_exit,

	.destroy = virtual_context_destroy,
};

static intel_engine_mask_t virtual_submission_mask(struct virtual_engine *ve)
{
	struct i915_request *rq;
	intel_engine_mask_t mask;

	rq = READ_ONCE(ve->request);
	if (!rq)
		return 0;

	/* The rq is ready for submission; rq->execution_mask is now stable. */
	mask = rq->execution_mask;
	if (unlikely(!mask)) {
		/* Invalid selection, submit to a random engine in error */
		i915_request_set_error_once(rq, -ENODEV);
		mask = ve->siblings[0]->mask;
	}

	ENGINE_TRACE(&ve->base, "rq=%llx:%lld, mask=%x, prio=%d\n",
		     rq->fence.context, rq->fence.seqno,
		     mask, ve->base.sched_engine->queue_priority_hint);

	return mask;
}

static void virtual_submission_tasklet(struct tasklet_struct *t)
{
	struct i915_sched_engine *sched_engine =
		from_tasklet(sched_engine, t, tasklet);
	struct virtual_engine * const ve =
		(struct virtual_engine *)sched_engine->private_data;
	const int prio = READ_ONCE(sched_engine->queue_priority_hint);
	intel_engine_mask_t mask;
	unsigned int n;

	rcu_read_lock();
	mask = virtual_submission_mask(ve);
	rcu_read_unlock();
	if (unlikely(!mask))
		return;

	for (n = 0; n < ve->num_siblings; n++) {
		struct intel_engine_cs *sibling = READ_ONCE(ve->siblings[n]);
		struct ve_node * const node = &ve->nodes[sibling->id];
		struct rb_node **parent, *rb;
		bool first;

		if (!READ_ONCE(ve->request))
			break; /* already handled by a sibling's tasklet */

		spin_lock_irq(&sibling->sched_engine->lock);

		if (unlikely(!(mask & sibling->mask))) {
			if (!RB_EMPTY_NODE(&node->rb)) {
				rb_erase_cached(&node->rb,
						&sibling->execlists.virtual);
				RB_CLEAR_NODE(&node->rb);
			}

			goto unlock_engine;
		}

		if (unlikely(!RB_EMPTY_NODE(&node->rb))) {
			/*
			 * Cheat and avoid rebalancing the tree if we can
			 * reuse this node in situ.
			 */
			first = rb_first_cached(&sibling->execlists.virtual) ==
				&node->rb;
			if (prio == node->prio || (prio > node->prio && first))
				goto submit_engine;

			rb_erase_cached(&node->rb, &sibling->execlists.virtual);
		}

		rb = NULL;
		first = true;
		parent = &sibling->execlists.virtual.rb_root.rb_node;
		while (*parent) {
			struct ve_node *other;

			rb = *parent;
			other = rb_entry(rb, typeof(*other), rb);
			if (prio > other->prio) {
				parent = &rb->rb_left;
			} else {
				parent = &rb->rb_right;
				first = false;
			}
		}

		rb_link_node(&node->rb, rb, parent);
		rb_insert_color_cached(&node->rb,
				       &sibling->execlists.virtual,
				       first);

submit_engine:
		GEM_BUG_ON(RB_EMPTY_NODE(&node->rb));
		node->prio = prio;
		if (first && prio > sibling->sched_engine->queue_priority_hint)
			tasklet_hi_schedule(&sibling->sched_engine->tasklet);

unlock_engine:
		spin_unlock_irq(&sibling->sched_engine->lock);

		if (intel_context_inflight(&ve->context))
			break;
	}
}

static void virtual_submit_request(struct i915_request *rq)
{
	struct virtual_engine *ve = to_virtual_engine(rq->engine);
	unsigned long flags;

	ENGINE_TRACE(&ve->base, "rq=%llx:%lld\n",
		     rq->fence.context,
		     rq->fence.seqno);

	GEM_BUG_ON(ve->base.submit_request != virtual_submit_request);

	spin_lock_irqsave(&ve->base.sched_engine->lock, flags);

	/* By the time we resubmit a request, it may be completed */
	if (__i915_request_is_complete(rq)) {
		__i915_request_submit(rq);
		goto unlock;
	}

	if (ve->request) { /* background completion from preempt-to-busy */
		GEM_BUG_ON(!__i915_request_is_complete(ve->request));
		__i915_request_submit(ve->request);
		i915_request_put(ve->request);
	}

	ve->base.sched_engine->queue_priority_hint = rq_prio(rq);
	ve->request = i915_request_get(rq);

	GEM_BUG_ON(!list_empty(virtual_queue(ve)));
	list_move_tail(&rq->sched.link, virtual_queue(ve));

	tasklet_hi_schedule(&ve->base.sched_engine->tasklet);

unlock:
	spin_unlock_irqrestore(&ve->base.sched_engine->lock, flags);
}

static struct ve_bond *
virtual_find_bond(struct virtual_engine *ve,
		  const struct intel_engine_cs *master)
{
	int i;

	for (i = 0; i < ve->num_bonds; i++) {
		if (ve->bonds[i].master == master)
			return &ve->bonds[i];
	}

	return NULL;
}

static void
virtual_bond_execute(struct i915_request *rq, struct dma_fence *signal)
{
	struct virtual_engine *ve = to_virtual_engine(rq->engine);
	intel_engine_mask_t allowed, exec;
	struct ve_bond *bond;

	allowed = ~to_request(signal)->engine->mask;

	bond = virtual_find_bond(ve, to_request(signal)->engine);
	if (bond)
		allowed &= bond->sibling_mask;

	/* Restrict the bonded request to run on only the available engines */
	exec = READ_ONCE(rq->execution_mask);
	while (!try_cmpxchg(&rq->execution_mask, &exec, exec & allowed))
		;

	/* Prevent the master from being re-run on the bonded engines */
	to_request(signal)->execution_mask &= ~allowed;
}

struct intel_context *
intel_execlists_create_virtual(struct intel_engine_cs **siblings,
			       unsigned int count)
{
	struct virtual_engine *ve;
	unsigned int n;
	int err;

	if (count == 0)
		return ERR_PTR(-EINVAL);

	if (count == 1)
		return intel_context_create(siblings[0]);

	ve = kzalloc(struct_size(ve, siblings, count), GFP_KERNEL);
	if (!ve)
		return ERR_PTR(-ENOMEM);

	ve->base.i915 = siblings[0]->i915;
	ve->base.gt = siblings[0]->gt;
	ve->base.uncore = siblings[0]->uncore;
	ve->base.id = -1;

	ve->base.class = OTHER_CLASS;
	ve->base.uabi_class = I915_ENGINE_CLASS_INVALID;
	ve->base.instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;
	ve->base.uabi_instance = I915_ENGINE_CLASS_INVALID_VIRTUAL;

	/*
	 * The decision on whether to submit a request using semaphores
	 * depends on the saturated state of the engine. We only compute
	 * this during HW submission of the request, and we need for this
	 * state to be globally applied to all requests being submitted
	 * to this engine. Virtual engines encompass more than one physical
	 * engine and so we cannot accurately tell in advance if one of those
	 * engines is already saturated and so cannot afford to use a semaphore
	 * and be pessimized in priority for doing so -- if we are the only
	 * context using semaphores after all other clients have stopped, we
	 * will be starved on the saturated system. Such a global switch for
	 * semaphores is less than ideal, but alas is the current compromise.
	 */
	ve->base.saturated = ALL_ENGINES;

	snprintf(ve->base.name, sizeof(ve->base.name), "virtual");

	intel_engine_init_execlists(&ve->base);

	ve->base.sched_engine = i915_sched_engine_create(ENGINE_VIRTUAL);
	if (!ve->base.sched_engine) {
		err = -ENOMEM;
		goto err_put;
	}
	ve->base.sched_engine->private_data = &ve->base;

	ve->base.cops = &virtual_context_ops;
	ve->base.request_alloc = execlists_request_alloc;

	ve->base.sched_engine->schedule = i915_schedule;
	ve->base.sched_engine->kick_backend = kick_execlists;
	ve->base.submit_request = virtual_submit_request;
	ve->base.bond_execute = virtual_bond_execute;

	INIT_LIST_HEAD(virtual_queue(ve));
	tasklet_setup(&ve->base.sched_engine->tasklet, virtual_submission_tasklet);

	intel_context_init(&ve->context, &ve->base);

	ve->base.breadcrumbs = intel_breadcrumbs_create(NULL);
	if (!ve->base.breadcrumbs) {
		err = -ENOMEM;
		goto err_put;
	}

	for (n = 0; n < count; n++) {
		struct intel_engine_cs *sibling = siblings[n];

		GEM_BUG_ON(!is_power_of_2(sibling->mask));
		if (sibling->mask & ve->base.mask) {
			DRM_DEBUG("duplicate %s entry in load balancer\n",
				  sibling->name);
			err = -EINVAL;
			goto err_put;
		}

		/*
		 * The virtual engine implementation is tightly coupled to
		 * the execlists backend -- we push out request directly
		 * into a tree inside each physical engine. We could support
		 * layering if we handle cloning of the requests and
		 * submitting a copy into each backend.
		 */
		if (sibling->sched_engine->tasklet.callback !=
		    execlists_submission_tasklet) {
			err = -ENODEV;
			goto err_put;
		}

		GEM_BUG_ON(RB_EMPTY_NODE(&ve->nodes[sibling->id].rb));
		RB_CLEAR_NODE(&ve->nodes[sibling->id].rb);

		ve->siblings[ve->num_siblings++] = sibling;
		ve->base.mask |= sibling->mask;

		/*
		 * All physical engines must be compatible for their emission
		 * functions (as we build the instructions during request
		 * construction and do not alter them before submission
		 * on the physical engine). We use the engine class as a guide
		 * here, although that could be refined.
		 */
		if (ve->base.class != OTHER_CLASS) {
			if (ve->base.class != sibling->class) {
				DRM_DEBUG("invalid mixing of engine class, sibling %d, already %d\n",
					  sibling->class, ve->base.class);
				err = -EINVAL;
				goto err_put;
			}
			continue;
		}

		ve->base.class = sibling->class;
		ve->base.uabi_class = sibling->uabi_class;
		snprintf(ve->base.name, sizeof(ve->base.name),
			 "v%dx%d", ve->base.class, count);
		ve->base.context_size = sibling->context_size;

		ve->base.emit_bb_start = sibling->emit_bb_start;
		ve->base.emit_flush = sibling->emit_flush;
		ve->base.emit_init_breadcrumb = sibling->emit_init_breadcrumb;
		ve->base.emit_fini_breadcrumb = sibling->emit_fini_breadcrumb;
		ve->base.emit_fini_breadcrumb_dw =
			sibling->emit_fini_breadcrumb_dw;

		ve->base.flags = sibling->flags;
	}

	ve->base.flags |= I915_ENGINE_IS_VIRTUAL;

	virtual_engine_initial_hint(ve);
	return &ve->context;

err_put:
	intel_context_put(&ve->context);
	return ERR_PTR(err);
}

struct intel_context *
intel_execlists_clone_virtual(struct intel_engine_cs *src)
{
	struct virtual_engine *se = to_virtual_engine(src);
	struct intel_context *dst;

	dst = intel_execlists_create_virtual(se->siblings,
					     se->num_siblings);
	if (IS_ERR(dst))
		return dst;

	if (se->num_bonds) {
		struct virtual_engine *de = to_virtual_engine(dst->engine);

		de->bonds = kmemdup(se->bonds,
				    sizeof(*se->bonds) * se->num_bonds,
				    GFP_KERNEL);
		if (!de->bonds) {
			intel_context_put(dst);
			return ERR_PTR(-ENOMEM);
		}

		de->num_bonds = se->num_bonds;
	}

	return dst;
}

int intel_virtual_engine_attach_bond(struct intel_engine_cs *engine,
				     const struct intel_engine_cs *master,
				     const struct intel_engine_cs *sibling)
{
	struct virtual_engine *ve = to_virtual_engine(engine);
	struct ve_bond *bond;
	int n;

	/* Sanity check the sibling is part of the virtual engine */
	for (n = 0; n < ve->num_siblings; n++)
		if (sibling == ve->siblings[n])
			break;
	if (n == ve->num_siblings)
		return -EINVAL;

	bond = virtual_find_bond(ve, master);
	if (bond) {
		bond->sibling_mask |= sibling->mask;
		return 0;
	}

	bond = krealloc(ve->bonds,
			sizeof(*bond) * (ve->num_bonds + 1),
			GFP_KERNEL);
	if (!bond)
		return -ENOMEM;

	bond[ve->num_bonds].master = master;
	bond[ve->num_bonds].sibling_mask = sibling->mask;

	ve->bonds = bond;
	ve->num_bonds++;

	return 0;
}

void intel_execlists_show_requests(struct intel_engine_cs *engine,
				   struct drm_printer *m,
				   void (*show_request)(struct drm_printer *m,
							const struct i915_request *rq,
							const char *prefix,
							int indent),
				   unsigned int max)
{
	const struct intel_engine_execlists *execlists = &engine->execlists;
	struct i915_sched_engine *sched_engine = engine->sched_engine;
	struct i915_request *rq, *last;
	unsigned long flags;
	unsigned int count;
	struct rb_node *rb;

	spin_lock_irqsave(&sched_engine->lock, flags);

	last = NULL;
	count = 0;
	list_for_each_entry(rq, &sched_engine->requests, sched.link) {
		if (count++ < max - 1)
			show_request(m, rq, "\t\t", 0);
		else
			last = rq;
	}
	if (last) {
		if (count > max) {
			drm_printf(m,
				   "\t\t...skipping %d executing requests...\n",
				   count - max);
		}
		show_request(m, last, "\t\t", 0);
	}

	if (sched_engine->queue_priority_hint != INT_MIN)
		drm_printf(m, "\t\tQueue priority hint: %d\n",
			   READ_ONCE(sched_engine->queue_priority_hint));

	last = NULL;
	count = 0;
	for (rb = rb_first_cached(&sched_engine->queue); rb; rb = rb_next(rb)) {
		struct i915_priolist *p = rb_entry(rb, typeof(*p), node);

		priolist_for_each_request(rq, p) {
			if (count++ < max - 1)
				show_request(m, rq, "\t\t", 0);
			else
				last = rq;
		}
	}
	if (last) {
		if (count > max) {
			drm_printf(m,
				   "\t\t...skipping %d queued requests...\n",
				   count - max);
		}
		show_request(m, last, "\t\t", 0);
	}

	last = NULL;
	count = 0;
	for (rb = rb_first_cached(&execlists->virtual); rb; rb = rb_next(rb)) {
		struct virtual_engine *ve =
			rb_entry(rb, typeof(*ve), nodes[engine->id].rb);
		struct i915_request *rq = READ_ONCE(ve->request);

		if (rq) {
			if (count++ < max - 1)
				show_request(m, rq, "\t\t", 0);
			else
				last = rq;
		}
	}
	if (last) {
		if (count > max) {
			drm_printf(m,
				   "\t\t...skipping %d virtual requests...\n",
				   count - max);
		}
		show_request(m, last, "\t\t", 0);
	}

	spin_unlock_irqrestore(&sched_engine->lock, flags);
}

#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
#include "selftest_execlists.c"
#endif
