drm/i915: stop using seqcount for fence pruning

After waiting for a reservation object use reservation_object_test_signaled_rcu
to opportunistically prune the fences on the object.

This allows removal of the seqcount handling in the reservation object.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/322032/?series=64786&rev=1

drivers/gpu/drm/i915/gem/i915_gem_wait.c

@@ -35,7 +35,6 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 				 unsigned int flags,
 				 long timeout)
 {
-	unsigned int seq = __read_seqcount_begin(&resv->seq);
 	struct dma_fence *excl;
 	bool prune_fences = false;
 
@@ -83,15 +82,12 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 
 	/*
 	 * Opportunistically prune the fences iff we know they have *all* been
-	 * signaled and that the reservation object has not been changed (i.e.
+	 * signaled.
-	 * no new fences have been added).
 	 */
-	if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
+	if (prune_fences && reservation_object_trylock(resv)) {
-		if (reservation_object_trylock(resv)) {
+		if (reservation_object_test_signaled_rcu(resv, true))
-			if (!__read_seqcount_retry(&resv->seq, seq))
+			reservation_object_add_excl_fence(resv, NULL);
-				reservation_object_add_excl_fence(resv, NULL);
+		reservation_object_unlock(resv);
-			reservation_object_unlock(resv);
-		}
 	}
 
 	return timeout;