When drm_crtc_init_with_planes() was orignally added
(in drm_crtc.c, e13161af
drm: Add drm_crtc_init_with_planes() (v2)), it only checked for "primary"
being non-null. If that was the case, it modified primary->possible_crtcs.

Then, when support for cursor planes was added
(fc1d3e44 drm: Allow drivers to register
cursor planes with crtc), the same behaviour was implemented for cursor
planes.

vc4_plane_init() since its inception has passed 0xff as "possible_crtcs"
parameter to drm_universal_plane_init(). With a change in drm_crtc.c
(7abc7d47 drm: don't override
possible_crtcs for primary/cursor planes) passing 0xff results in primary's
possible_crtcs set to 0xff (cursor was updated manually by vc4_crtc.c).
Consequently, it would be allowed to use the primary plane from CRTC 1 (for
example) on CRTC 0, which would result in the overlay and cursors being
buried.
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/1485941708-27892-1-git-send-email-andrzej.p@samsung.com
Fixes: 7abc7d47 ("drm: don't override possible_crtcs for primary/cursor planes")