[PATCH] drm/sun4i: backend: fix error pointer dereference

[Ethan Tidmore <ethantidmore06@gmail.com>]

The function drm_atomic_get_plane_state() can return an error pointer
and is not checked for it. Add error pointer check.

Detected by Smatch:
drivers/gpu/drm/sun4i/sun4i_backend.c:496 sun4i_backend_atomic_check() error:
'plane_state' dereferencing possible ERR_PTR()

Fixes: 96180dde23b79 ("drm/sun4i: backend: Add a custom atomic_check for the frontend")
Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
---
 drivers/gpu/drm/sun4i/sun4i_backend.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
index 40405a52a073..6391bdc94a5c 100644
--- a/drivers/gpu/drm/sun4i/sun4i_backend.c
+++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
@@ -491,6 +491,9 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
 	drm_for_each_plane_mask(plane, drm, crtc_state->plane_mask) {
 		struct drm_plane_state *plane_state =
 			drm_atomic_get_plane_state(state, plane);
+		if (IS_ERR(plane_state))
+			return PTR_ERR(plane_state);
+
 		struct sun4i_layer_state *layer_state =
 			state_to_sun4i_layer_state(plane_state);
 		struct drm_framebuffer *fb = plane_state->fb;
-- 
2.53.0