drm/sun4i: backend: fix error pointer dereference

[ Upstream commit 0627798 ]

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: 96180dd ("drm/sun4i: backend: Add a custom atomic_check for the frontend")
Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@kernel.org>
Link: https://patch.msgid.link/20260217014801.60760-1-ethantidmore06@gmail.com
Signed-off-by: Chen-Yu Tsai <wens@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Ethan Tidmore

drivers/gpu/drm/sun4i/sun4i_backend.c

@@ -488,6 +488,9 @@ 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;