[PATCH] drm: don't override possible_crtcs for primary/cursor planes

[Rob Clark]

It is kind of a pointless restriction.  If userspace does silly things
like using crtcA's cursor plane on crtcB, and then setcursor on crtcA,
it will end up with the overlay disabled on crtcB.  But userspace is
allowed to shoot itself like this.

Signed-off-by: Rob Clark <robdclark at gmail.com>
---
Note that cursor and primary planes are slightly useless to non-atomic
userspace, since userspace has no way to know *which* crtc a primary
or cursor plane belongs to.  So lighting up a 2nd display may or may
not make your overlay planes go *poof*.

So basically use of cursor/primary planes plus legacy ioctls is an
undefined behavior if we go with this patch.

*Maybe* we want to restrict this to atomic userspace.  (Ie. advertise
the more limited possible_crtcs for legacy userspace.)  Depends on
whether we can (slightly retroactively) declare that mixing atomic
and legacy APIs is undefined behavior.  Or if really needed, add
DRM_CLIENT_CAP_REALLY_REALLY_ATOMIC_NO_LEGACY_PLS.  (Or just pass in
value 2 for existing DRM_CLIENT_CAP_ATOMIC)

 drivers/gpu/drm/drm_crtc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index c215802..1e6d37f 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -707,9 +707,9 @@ int drm_crtc_init_with_planes(struct drm_device *dev, struct drm_crtc *crtc,
 	crtc->primary = primary;
 	crtc->cursor = cursor;
 	if (primary)
-		primary->possible_crtcs = 1 << drm_crtc_index(crtc);
+		WARN_ON(!(primary->possible_crtcs & (1 << drm_crtc_index(crtc))));
 	if (cursor)
-		cursor->possible_crtcs = 1 << drm_crtc_index(crtc);
+		WARN_ON(!(cursor->possible_crtcs & (1 << drm_crtc_index(crtc))));
 
 	if (drm_core_check_feature(dev, DRIVER_ATOMIC)) {
 		drm_object_attach_property(&crtc->base, config->prop_active, 0);
-- 
2.7.4