drm/i915: Ensure OLS & PLR are always in sync

The aim is to replace seqno values with request structures. A step along the way
is to switch to using the PLR in preference to the OLS. That requires the PLR to
only be valid when and only when the OLS is also valid. I.e., the two must be
kept in lock step. Then, code which was using the OLS can be safely switched
over to using the PLR instead.

For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Thomas Daniel <Thomas.Daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -879,37 +879,48 @@ void intel_lr_context_unpin(struct intel_engine_cs *ring,
 static int logical_ring_alloc_seqno(struct intel_engine_cs *ring,
 				    struct intel_context *ctx)
 {
+	struct drm_i915_gem_request *request;
 	int ret;
 
-	if (ring->outstanding_lazy_seqno)
-		return 0;
+	/* XXX: The aim is to replace seqno values with request structures.
+	 * A step along the way is to switch to using the PLR in preference
+	 * to the OLS. That requires the PLR to only be valid when the OLS is
+	 * also valid. I.e., the two must be kept in step. */
 
-	if (ring->preallocated_lazy_request == NULL) {
-		struct drm_i915_gem_request *request;
+	if (ring->outstanding_lazy_seqno) {
+		WARN_ON(ring->preallocated_lazy_request == NULL);
+		return 0;
+	}
+	WARN_ON(ring->preallocated_lazy_request != NULL);
 
-		request = kmalloc(sizeof(*request), GFP_KERNEL);
-		if (request == NULL)
-			return -ENOMEM;
+	request = kmalloc(sizeof(*request), GFP_KERNEL);
+	if (request == NULL)
+		return -ENOMEM;
 
-		if (ctx != ring->default_context) {
-			ret = intel_lr_context_pin(ring, ctx);
-			if (ret) {
-				kfree(request);
-				return ret;
-			}
+	if (ctx != ring->default_context) {
+		ret = intel_lr_context_pin(ring, ctx);
+		if (ret) {
+			kfree(request);
+			return ret;
 		}
+	}
 
-		/* Hold a reference to the context this request belongs to
-		 * (we will need it when the time comes to emit/retire the
-		 * request).
-		 */
-		request->ctx = ctx;
-		i915_gem_context_reference(request->ctx);
-
-		ring->preallocated_lazy_request = request;
+	ret = i915_gem_get_seqno(ring->dev, &ring->outstanding_lazy_seqno);
+	if (ret) {
+		intel_lr_context_unpin(ring, ctx);
+		kfree(request);
+		return ret;
 	}
 
-	return i915_gem_get_seqno(ring->dev, &ring->outstanding_lazy_seqno);
+	/* Hold a reference to the context this request belongs to
+	 * (we will need it when the time comes to emit/retire the
+	 * request).
+	 */
+	request->ctx = ctx;
+	i915_gem_context_reference(request->ctx);
+
+	ring->preallocated_lazy_request = request;
+	return 0;
 }
 
 static int logical_ring_wait_request(struct intel_ringbuffer *ringbuf,

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2024,20 +2024,33 @@ int intel_ring_idle(struct intel_engine_cs *ring)
 static int
 intel_ring_alloc_seqno(struct intel_engine_cs *ring)
 {
-	if (ring->outstanding_lazy_seqno)
+	int ret;
+	struct drm_i915_gem_request *request;
+
+	/* XXX: The aim is to replace seqno values with request structures.
+	 * A step along the way is to switch to using the PLR in preference
+	 * to the OLS. That requires the PLR to only be valid when the OLS
+	 * is also valid. I.e., the two must be kept in step. */
+
+	if (ring->outstanding_lazy_seqno) {
+		WARN_ON(ring->preallocated_lazy_request == NULL);
 		return 0;
+	}
 
-	if (ring->preallocated_lazy_request == NULL) {
-		struct drm_i915_gem_request *request;
+	WARN_ON(ring->preallocated_lazy_request != NULL);
 
-		request = kmalloc(sizeof(*request), GFP_KERNEL);
-		if (request == NULL)
-			return -ENOMEM;
+	request = kmalloc(sizeof(*request), GFP_KERNEL);
+	if (request == NULL)
+		return -ENOMEM;
 
-		ring->preallocated_lazy_request = request;
+	ret = i915_gem_get_seqno(ring->dev, &ring->outstanding_lazy_seqno);
+	if (ret) {
+		kfree(request);
+		return ret;
 	}
 
-	return i915_gem_get_seqno(ring->dev, &ring->outstanding_lazy_seqno);
+	ring->preallocated_lazy_request = request;
+	return 0;
 }
 
 static int __intel_ring_prepare(struct intel_engine_cs *ring,