[PATCH v3 4/9] drm/vc4: Use wait_for_flip_done() instead of wait_for_vblanks()

[Boris Brezillon]

drm_atomic_helper_wait_for_vblanks() assumes the CRTC will continuously
generate VBLANK events and the vblank counter will keep increasing.
While this work for a regular pipeline, it doesn't when you have the
CRTC is feeding the transposer block, because this block works in
oneshot mode, and, by the time we reach
drm_atomic_helper_wait_for_vblanks() the only VBLANK event might have
already been sent and the VBLANK counter will stay unchanged, thus
triggering a timeout.

Luckily, we can replace the drm_atomic_helper_wait_for_vblanks() call
by drm_atomic_helper_wait_for_flip_done() because the only thing we
want to check when calling drm_atomic_helper_wait_for_vblanks() from
vc4_atomic_complete_commit() is that new FBs are in use and the old
ones can be safely released.

Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>
Reviewed-by: Liviu Dudau <liviu.dudau at arm.com>
Reviewed-by: Eric Anholt <eric at anholt.net>
---
Changes in v3:
- Add Eric's and Liviu's R-b

Changes in v2:
- None
---
 drivers/gpu/drm/vc4/vc4_kms.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 8a411e5f8776..91239b0a4fa0 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -153,18 +153,9 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
 
 	drm_atomic_helper_commit_modeset_enables(dev, state);
 
-	/* Make sure that drm_atomic_helper_wait_for_vblanks()
-	 * actually waits for vblank.  If we're doing a full atomic
-	 * modeset (as opposed to a vc4_update_plane() short circuit),
-	 * then we need to wait for scanout to be done with our
-	 * display lists before we free it and potentially reallocate
-	 * and overwrite the dlist memory with a new modeset.
-	 */
-	state->legacy_cursor_update = false;
-
 	drm_atomic_helper_commit_hw_done(state);
 
-	drm_atomic_helper_wait_for_vblanks(dev, state);
+	drm_atomic_helper_wait_for_flip_done(dev, state);
 
 	drm_atomic_helper_cleanup_planes(dev, state);
 
-- 
2.14.1