[PATCH 4.17 29/31] drm/atomic: Check old_plane_state->crtc in drm_atomic_helper_async_check()

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>

commit 603ba2dfb338b307aebe95fe344c479a59b3a175 upstream.

Async plane update is supposed to work only when updating the FB or FB
position of an already enabled plane. That does not apply to requests
where the plane was previously disabled or assigned to a different
CTRC.

Check old_plane_state->crtc value to make sure async plane update is
allowed.

Fixes: fef9df8b5945 ("drm/atomic: initial support for asynchronous plane update")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxx>
Reviewed-by: Eric Anholt <eric@xxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180724133215.31917-1-boris.brezillon@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/drm_atomic_helper.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1516,7 +1516,8 @@ int drm_atomic_helper_async_check(struct
 	if (n_planes != 1)
 		return -EINVAL;
 
-	if (!new_plane_state->crtc)
+	if (!new_plane_state->crtc ||
+	    old_plane_state->crtc != new_plane_state->crtc)
 		return -EINVAL;
 
 	funcs = plane->helper_private;