drm/i915: Mark the addition of the initial-breadcrumb in the request

The initial-breadcrumb is used to mark the end of the awaiting and the
beginning of the user payload. We verify that we do not start the user
payload before all signaler are completed, checking our semaphore setup
by looking for the initial breadcrumb being written too early. We also
want to ensure that we do not add semaphore waits after we have already
closed the semaphore section, an issue for later deferred waits.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200513165937.9508-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1886,7 +1886,7 @@ static void defer_request(struct i915_request *rq, struct list_head * const pl)
 				continue;
 
 			/* No waiter should start before its signaler */
-			GEM_BUG_ON(w->context->timeline->has_initial_breadcrumb &&
+			GEM_BUG_ON(i915_request_has_initial_breadcrumb(w) &&
 				   i915_request_started(w) &&
 				   !i915_request_completed(rq));
 
@@ -3493,6 +3493,7 @@ static int gen8_emit_init_breadcrumb(struct i915_request *rq)
 {
 	u32 *cs;
 
+	GEM_BUG_ON(i915_request_has_initial_breadcrumb(rq));
 	if (!i915_request_timeline(rq)->has_initial_breadcrumb)
 		return 0;
 
@@ -3519,6 +3520,8 @@ static int gen8_emit_init_breadcrumb(struct i915_request *rq)
 	/* Record the updated position of the request's payload */
 	rq->infix = intel_ring_offset(rq, cs);
 
+	__set_bit(I915_FENCE_FLAG_INITIAL_BREADCRUMB, &rq->fence.flags);
+
 	return 0;
 }
 

drivers/gpu/drm/i915/i915_request.c

@@ -951,6 +951,7 @@ __emit_semaphore_wait(struct i915_request *to,
 	u32 *cs;
 
 	GEM_BUG_ON(INTEL_GEN(to->i915) < 8);
+	GEM_BUG_ON(i915_request_has_initial_breadcrumb(to));
 
 	/* We need to pin the signaler's HWSP until we are finished reading. */
 	err = intel_timeline_read_hwsp(from, to, &hwsp_offset);
@@ -1000,6 +1001,9 @@ emit_semaphore_wait(struct i915_request *to,
 	if (!intel_context_use_semaphores(to->context))
 		goto await_fence;
 
+	if (i915_request_has_initial_breadcrumb(to))
+		goto await_fence;
+
 	if (!rcu_access_pointer(from->hwsp_cacheline))
 		goto await_fence;
 
@@ -1256,7 +1260,8 @@ __i915_request_await_execution(struct i915_request *to,
 	 * immediate execution, and so we must wait until it reaches the
 	 * active slot.
 	 */
-	if (intel_engine_has_semaphores(to->engine)) {
+	if (intel_engine_has_semaphores(to->engine) &&
+	    !i915_request_has_initial_breadcrumb(to)) {
 		err = __emit_semaphore_wait(to, from, from->fence.seqno - 1);
 		if (err < 0)
 			return err;

drivers/gpu/drm/i915/i915_request.h

@@ -84,19 +84,26 @@ enum {
 	I915_FENCE_FLAG_PQUEUE,
 
 	/*
-	 * I915_FENCE_FLAG_SIGNAL - this request is currently on signal_list
+	 * I915_FENCE_FLAG_HOLD - this request is currently on hold
 	 *
-	 * Internal bookkeeping used by the breadcrumb code to track when
-	 * a request is on the various signal_list.
+	 * This request has been suspended, pending an ongoing investigation.
 	 */
-	I915_FENCE_FLAG_SIGNAL,
+	I915_FENCE_FLAG_HOLD,
 
 	/*
-	 * I915_FENCE_FLAG_HOLD - this request is currently on hold
+	 * I915_FENCE_FLAG_INITIAL_BREADCRUMB - this request has the initial
+	 * breadcrumb that marks the end of semaphore waits and start of the
+	 * user payload.
+	 */
+	I915_FENCE_FLAG_INITIAL_BREADCRUMB,
+
+	/*
+	 * I915_FENCE_FLAG_SIGNAL - this request is currently on signal_list
 	 *
-	 * This request has been suspended, pending an ongoing investigation.
+	 * Internal bookkeeping used by the breadcrumb code to track when
+	 * a request is on the various signal_list.
 	 */
-	I915_FENCE_FLAG_HOLD,
+	I915_FENCE_FLAG_SIGNAL,
 
 	/*
 	 * I915_FENCE_FLAG_NOPREEMPT - this request should not be preempted
@@ -390,6 +397,12 @@ static inline bool i915_request_in_priority_queue(const struct i915_request *rq)
 	return test_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
 }
 
+static inline bool
+i915_request_has_initial_breadcrumb(const struct i915_request *rq)
+{
+	return test_bit(I915_FENCE_FLAG_INITIAL_BREADCRUMB, &rq->fence.flags);
+}
+
 /**
  * Returns true if seq1 is later than seq2.
  */