drm/i915/gvt: update RING_START reg of vGPU when the context is submitted to i915

The guest may use this register to identify the running state of one
context. Emulate it as the value in context image as if the context runs
on the GPU hardware.
Signed-off-by: Weinan Li <weinan.z.li@intel.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -573,6 +573,16 @@ static int prepare_shadow_wa_ctx(struct intel_shadow_wa_ctx *wa_ctx)
 	return 0;
 }
 
+static void update_vreg_in_ctx(struct intel_vgpu_workload *workload)
+{
+	struct intel_vgpu *vgpu = workload->vgpu;
+	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
+	u32 ring_base;
+
+	ring_base = dev_priv->engine[workload->ring_id]->mmio_base;
+	vgpu_vreg_t(vgpu, RING_START(ring_base)) = workload->rb_start;
+}
+
 static void release_shadow_batch_buffer(struct intel_vgpu_workload *workload)
 {
 	struct intel_vgpu *vgpu = workload->vgpu;
@@ -1002,6 +1012,13 @@ static int workload_thread(void *priv)
 		if (need_force_wake)
 			intel_uncore_forcewake_get(&gvt->dev_priv->uncore,
 					FORCEWAKE_ALL);
+		/*
+		 * Update the vReg of the vGPU which submitted this
+		 * workload. The vGPU may use these registers for checking
+		 * the context state. The value comes from GPU commands
+		 * in this workload.
+		 */
+		update_vreg_in_ctx(workload);
 
 		ret = dispatch_workload(workload);