drm/msm: Grab a vblank reference when waiting for commit_done

BugLink: https://bugs.launchpad.net/bugs/1811252

[ Upstream commit 3b712e43 ]

Similar to the atomic helpers, we should enable vblank while we're
waiting for the commit to finish. DPU needs this, MDP5 seems to work
fine without it.
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/gpu/drm/msm/msm_atomic.c

@@ -107,7 +107,12 @@ static void msm_atomic_wait_for_commit_done(struct drm_device *dev,
 		if (old_state->legacy_cursor_update)
 			continue;
 
+		if (drm_crtc_vblank_get(crtc))
+			continue;
+
 		kms->funcs->wait_for_crtc_commit_done(kms, crtc);
+
+		drm_crtc_vblank_put(crtc);
 	}
 }