drm/amd/display: Prevent premature pageflip when comitting in vblank. (v3)

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', unless this
is a DRM_MODE_PAGE_FLIP_ASYNC async pageflip, which must always
execute as soon as possible.

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.
v3: Feedback from Andrey: Must not wait an extra frame for
    DRM_MODE_PAGE_FLIP_ASYNC flips.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Acked-by: Harry Wentland <harry.wentland@amd.com> (v1)
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>

Cc: Harry Wentland <Harry.Wentland@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_types.c

@@ -2305,6 +2305,9 @@ 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
@@ -2323,13 +2326,9 @@ 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,
@@ -2605,14 +2604,15 @@ void amdgpu_dm_atomic_commit_tail(
 		pflip_needed = !state->allow_modeset;
 
 		if (pflip_needed) {
+			wait_for_vblank =
+				acrtc->flip_flags & DRM_MODE_PAGE_FLIP_ASYNC ?
+				false : true;
+
 			amdgpu_dm_do_flip(
-					crtc,
-					fb,
-					drm_crtc_vblank_count(crtc));
+				crtc,
+				fb,
+				drm_crtc_vblank_count(crtc) + wait_for_vblank);
 
-			wait_for_vblank =
-					acrtc->flip_flags & DRM_MODE_PAGE_FLIP_ASYNC ?
-							false : true;
 			/*clean up the flags for next usage*/
 			acrtc->flip_flags = 0;
 		}