drm/i915/gvt: save RING_HEAD into vreg when vgpu switched out

Save RING_HEAD into vgpu reg when vgpu switched out and report
it's value back to guest.

v6: addressed comment for ring head wrap count support. (Zhenyu)
v5: ring head wrap count support.
v4: updated HEAD/TAIL with guest value, not host value. (Yan Zhao)
v3: save RING HEAD/TAIL vgpu reg in save_ring_hw_state. (Zhenyu Wang)
v2: save RING_TAIL as well during vgpu mmio switch to meet ring_is_idle
condition. (Fred Gao)
v1: based on input from Weinan. (Weinan Li)

[zhenyuw: Include this fix for possible future guest kernel that
would utilize RING_HEAD for hangcheck.]
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/reg.h

@@ -102,6 +102,8 @@
 #define FORCEWAKE_ACK_MEDIA_GEN9_REG 0x0D88
 #define FORCEWAKE_ACK_HSW_REG 0x130044
 
+#define RB_HEAD_WRAP_CNT_MAX	((1 << 11) - 1)
+#define RB_HEAD_WRAP_CNT_OFF	21
 #define RB_HEAD_OFF_MASK	((1U << 21) - (1U << 2))
 #define RB_TAIL_OFF_MASK	((1U << 21) - (1U << 3))
 #define RB_TAIL_SIZE_MASK	((1U << 21) - (1U << 12))

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -812,10 +812,31 @@ static void update_guest_context(struct intel_vgpu_workload *workload)
 	void *src;
 	unsigned long context_gpa, context_page_num;
 	int i;
+	struct drm_i915_private *dev_priv = gvt->dev_priv;
+	u32 ring_base;
+	u32 head, tail;
+	u16 wrap_count;
 
 	gvt_dbg_sched("ring id %d workload lrca %x\n", rq->engine->id,
 		      workload->ctx_desc.lrca);
 
+	head = workload->rb_head;
+	tail = workload->rb_tail;
+	wrap_count = workload->guest_rb_head >> RB_HEAD_WRAP_CNT_OFF;
+
+	if (tail < head) {
+		if (wrap_count == RB_HEAD_WRAP_CNT_MAX)
+			wrap_count = 0;
+		else
+			wrap_count += 1;
+	}
+
+	head = (wrap_count << RB_HEAD_WRAP_CNT_OFF) | tail;
+
+	ring_base = dev_priv->engine[workload->ring_id]->mmio_base;
+	vgpu_vreg_t(vgpu, RING_TAIL(ring_base)) = tail;
+	vgpu_vreg_t(vgpu, RING_HEAD(ring_base)) = head;
+
 	context_page_num = rq->engine->context_size;
 	context_page_num = context_page_num >> PAGE_SHIFT;
 
@@ -1415,6 +1436,7 @@ intel_vgpu_create_workload(struct intel_vgpu *vgpu, int ring_id,
 	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
 	u64 ring_context_gpa;
 	u32 head, tail, start, ctl, ctx_ctl, per_ctx, indirect_ctx;
+	u32 guest_head;
 	int ret;
 
 	ring_context_gpa = intel_vgpu_gma_to_gpa(vgpu->gtt.ggtt_mm,
@@ -1430,6 +1452,8 @@ intel_vgpu_create_workload(struct intel_vgpu *vgpu, int ring_id,
 	intel_gvt_hypervisor_read_gpa(vgpu, ring_context_gpa +
 			RING_CTX_OFF(ring_tail.val), &tail, 4);
 
+	guest_head = head;
+
 	head &= RB_HEAD_OFF_MASK;
 	tail &= RB_TAIL_OFF_MASK;
 
@@ -1462,6 +1486,7 @@ intel_vgpu_create_workload(struct intel_vgpu *vgpu, int ring_id,
 	workload->ctx_desc = *desc;
 	workload->ring_context_gpa = ring_context_gpa;
 	workload->rb_head = head;
+	workload->guest_rb_head = guest_head;
 	workload->rb_tail = tail;
 	workload->rb_start = start;
 	workload->rb_ctl = ctl;

drivers/gpu/drm/i915/gvt/scheduler.h

@@ -100,6 +100,7 @@ struct intel_vgpu_workload {
 	struct execlist_ctx_descriptor_format ctx_desc;
 	struct execlist_ring_context *ring_context;
 	unsigned long rb_head, rb_tail, rb_ctl, rb_start, rb_len;
+	unsigned long guest_rb_head;
 	bool restore_inhibit;
 	struct intel_vgpu_elsp_dwords elsp_dwords;
 	bool emulate_schedule_in;