[PATCH 2/2] drm/amd/display: Prevent premature pageflip when comitting in vblank. (v2)

[Mario Kleiner]

Make sure we do not program a hw pageflip inside vblank 'n' iff the
atomic flip is comitted while inside the same vblank 'n'. We must
defer such a flip by one refresh cycle to vblank 'n+1'.

Without this, pageflips programmed via X11 GLX_OML_sync_control extensions
glXSwapBuffersMscOML(..., target_msc, ...); call and/or via DRI3/Present
PresentPixmap(..., target_msc, ...); request will complete one vblank
too early whenever target_msc > current_msc + 1, ie. more than 1 vblank
in the future. In such a case, the call of the pageflip ioctl() would be
triggered by a queued drmWaitVblank() vblank event, which itself gets
dispatched inside the vblank one frame before the target_msc vblank.

Testing with this patch does no longer show any problems with
OML_sync_control swap scheduling or flip completion timestamps.
Tested on R9 380 Tonga.

v2: Add acked/r-b by Harry and Michel.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Acked-by: Harry Wentland <harry.wentland at amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer at amd.com>

Cc: Harry Wentland <Harry.Wentland at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Michel Dänzer <michel.daenzer at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c
index 086a842..19be2d9 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c
@@ -2460,6 +2460,9 @@ static void amdgpu_dm_do_flip(
 	struct amdgpu_device *adev = crtc->dev->dev_private;
 	bool async_flip = (acrtc->flip_flags & DRM_MODE_PAGE_FLIP_ASYNC) != 0;
 
+	/* Prepare wait for target vblank early - before the fence-waits */
+	target_vblank = target - drm_crtc_vblank_count(crtc) +
+			amdgpu_get_vblank_counter_kms(crtc->dev, acrtc->crtc_id);
 
 	/*TODO This might fail and hence better not used, wait
 	 * explicitly on fences instead
@@ -2478,13 +2481,9 @@ static void amdgpu_dm_do_flip(
 
 	amdgpu_bo_unreserve(abo);
 
-	/* Wait for target vblank */
 	/* Wait until we're out of the vertical blank period before the one
 	 * targeted by the flip
 	 */
-	target_vblank = target - drm_crtc_vblank_count(crtc) +
-			amdgpu_get_vblank_counter_kms(crtc->dev, acrtc->crtc_id);
-
 	while ((acrtc->enabled &&
 		(amdgpu_get_crtc_scanoutpos(adev->ddev, acrtc->crtc_id, 0,
 					&vpos, &hpos, NULL, NULL,
@@ -2763,7 +2762,7 @@ void amdgpu_dm_atomic_commit_tail(
 			amdgpu_dm_do_flip(
 					crtc,
 					fb,
-					drm_crtc_vblank_count(crtc));
+					drm_crtc_vblank_count(crtc) + 1);
 
 			wait_for_vblank =
 					acrtc->flip_flags & DRM_MODE_PAGE_FLIP_ASYNC ?
-- 
2.7.4