drm: don't block fb changes for async plane updates

From Helen Koike
fbb7e114e6e690c46f170dedd6fd2fb22f241519 in linux 4.19.y/4.19.50
89a4aac0ab0e6f5eea10d7bf4869dd15c3de2cd4 in mainline linux

2 files changed, 20 insertions, 10 deletions

diff --git a/sys/dev/pci/drm/drm_atomic_helper.c b/sys/dev/pci/drm/drm_atomic_helper.c
index 37fcd892de4..57a1d3d6dbb 100644
--- a/sys/dev/pci/drm/drm_atomic_helper.c
+++ b/sys/dev/pci/drm/drm_atomic_helper.c
@@ -1578,15 +1578,6 @@ int drm_atomic_helper_async_check(struct drm_device *dev,
 	if (old_plane_state->fb != new_plane_state->fb)
 		return -EINVAL;
 
-	/*
-	 * FIXME: Since prepare_fb and cleanup_fb are always called on
-	 * the new_plane_state for async updates we need to block framebuffer
-	 * changes. This prevents use of a fb that's been cleaned up and
-	 * double cleanups from occuring.
-	 */
-	if (old_plane_state->fb != new_plane_state->fb)
-		return -EINVAL;
-
 	funcs = plane->helper_private;
 	if (!funcs->atomic_async_update)
 		return -EINVAL;
@@ -1617,6 +1608,8 @@ EXPORT_SYMBOL(drm_atomic_helper_async_check);
  * drm_atomic_async_check() succeeds. Async commits are not supposed to swap
  * the states like normal sync commits, but just do in-place changes on the
  * current state.
+ *
+ * TODO: Implement full swap instead of doing in-place changes.
  */
 void drm_atomic_helper_async_commit(struct drm_device *dev,
 				    struct drm_atomic_state *state)
@@ -1627,6 +1620,9 @@ void drm_atomic_helper_async_commit(struct drm_device *dev,
 	int i;
 
 	for_each_new_plane_in_state(state, plane, plane_state, i) {
+		struct drm_framebuffer *new_fb = plane_state->fb;
+		struct drm_framebuffer *old_fb = plane->state->fb;
+
 		funcs = plane->helper_private;
 		funcs->atomic_async_update(plane, plane_state);
 
@@ -1635,11 +1631,17 @@ void drm_atomic_helper_async_commit(struct drm_device *dev,
 		 * plane->state in-place, make sure at least common
 		 * properties have been properly updated.
 		 */
-		WARN_ON_ONCE(plane->state->fb != plane_state->fb);
+		WARN_ON_ONCE(plane->state->fb != new_fb);
 		WARN_ON_ONCE(plane->state->crtc_x != plane_state->crtc_x);
 		WARN_ON_ONCE(plane->state->crtc_y != plane_state->crtc_y);
 		WARN_ON_ONCE(plane->state->src_x != plane_state->src_x);
 		WARN_ON_ONCE(plane->state->src_y != plane_state->src_y);
+
+		/*
+		 * Make sure the FBs have been swapped so that cleanups in the
+		 * new_state performs a cleanup in the old FB.
+		 */
+		WARN_ON_ONCE(plane_state->fb != old_fb);
 	}
 }
 EXPORT_SYMBOL(drm_atomic_helper_async_commit);
diff --git a/sys/dev/pci/drm/include/drm/drm_modeset_helper_vtables.h b/sys/dev/pci/drm/include/drm/drm_modeset_helper_vtables.h
index 61142aa0ab2..0eb3372d031 100644
--- a/sys/dev/pci/drm/include/drm/drm_modeset_helper_vtables.h
+++ b/sys/dev/pci/drm/include/drm/drm_modeset_helper_vtables.h
@@ -1174,6 +1174,14 @@ struct drm_plane_helper_funcs {
 	 * current one with the new plane configurations in the new
 	 * plane_state.
 	 *
+	 * Drivers should also swap the framebuffers between current plane
+	 * state (&drm_plane.state) and new_state.
+	 * This is required since cleanup for async commits is performed on
+	 * the new state, rather than old state like for traditional commits.
+	 * Since we want to give up the reference on the current (old) fb
+	 * instead of our brand new one, swap them in the driver during the
+	 * async commit.
+	 *
 	 * FIXME:
 	 *  - It only works for single plane updates
 	 *  - Async Pageflips are not supported yet