[PATCH 5.16 078/126] drm: mxsfb: Fix NULL pointer dereference

[Greg Kroah-Hartman]

From: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>

commit 622c9a3a7868e1eeca39c55305ca3ebec4742b64 upstream.

mxsfb should not ever dereference the NULL pointer which
drm_atomic_get_new_bridge_state is allowed to return.
Assume a fixed format instead.

Fixes: b776b0f00f24 ("drm: mxsfb: Use bus_format from the nearest bridge if present")
Signed-off-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
Signed-off-by: Marek Vasut <marex@xxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20220202081755.145716-3-alexander.stein@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/mxsfb/mxsfb_kms.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
@@ -361,7 +361,11 @@ static void mxsfb_crtc_atomic_enable(str
 		bridge_state =
 			drm_atomic_get_new_bridge_state(state,
 							mxsfb->bridge);
-		bus_format = bridge_state->input_bus_cfg.format;
+		if (!bridge_state)
+			bus_format = MEDIA_BUS_FMT_FIXED;
+		else
+			bus_format = bridge_state->input_bus_cfg.format;
+
 		if (bus_format == MEDIA_BUS_FMT_FIXED) {
 			dev_warn_once(drm->dev,
 				      "Bridge does not provide bus format, assuming MEDIA_BUS_FMT_RGB888_1X24.\n"