drm: Reject modes with more than 1 stereo flags set

When setting a stereo 3D mode, there can be only one bit set describing
the layout of the frambuffer(s). So reject invalid modes early.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -1319,6 +1319,10 @@ static int drm_crtc_convert_umode(struct drm_display_mode *out,
 	if (in->clock > INT_MAX || in->vrefresh > INT_MAX)
 		return -ERANGE;
 
+	/* At most, 1 set bit describing the 3D layout of the mode */
+	if (hweight32(in->flags & DRM_MODE_FLAG_3D_MASK) > 1)
+		return -EINVAL;
+
 	out->clock = in->clock;
 	out->hdisplay = in->hdisplay;
 	out->hsync_start = in->hsync_start;