[PATCH v2] drm/imx: ipuv3-plane: Access old u/vbo properly in ->atomic_check for YU12/YV12

[Liu Ying]

Before accessing the u/v offset(aka, u/vbo for IPUv3) of the old plane state's
relevant fb, we should make sure the fb is in YU12 or YV12 pixel format(which
are the two YUV pixel formats we support only), otherwise, we are likely to
trigger BUG_ON() in drm_plane_state_to_u/vbo() since the fb's pixel format is
probably not YU12 or YV12.

Link: https://bugs.freedesktop.org/show_bug.cgi?id=98150
Fixes: c6c1f9bc798b ("drm/imx: Add active plane reconfiguration support")
Cc: stable at vger.kernel.org # 4.8
Signed-off-by: Liu Ying <gnuiyl at gmail.com>
---
v1->v2:
* Correct the condition under which we may access old u/vbo - old->pixel_format
  is not necessarily the same to fb->pixel_format, instead, it could be YU12
  or YV12.  This may cover the case in which we switch fb pixel format
  bewteen YU12 and YV12.

 drivers/gpu/drm/imx/ipuv3-plane.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/imx/ipuv3-plane.c b/drivers/gpu/drm/imx/ipuv3-plane.c
index e33110e..08d0fd5 100644
--- a/drivers/gpu/drm/imx/ipuv3-plane.c
+++ b/drivers/gpu/drm/imx/ipuv3-plane.c
@@ -359,7 +359,9 @@ static int ipu_plane_atomic_check(struct drm_plane *plane,
 		if ((ubo > 0xfffff8) || (vbo > 0xfffff8))
 			return -EINVAL;
 
-		if (old_fb) {
+		if (old_fb &&
+		    (old_fb->pixel_format == DRM_FORMAT_YUV420 ||
+		     old_fb->pixel_format == DRM_FORMAT_YVU420)) {
 			old_ubo = drm_plane_state_to_ubo(old_state);
 			old_vbo = drm_plane_state_to_vbo(old_state);
 			if (ubo != old_ubo || vbo != old_vbo)
-- 
2.7.4