Re: [PATCH] drm/atomic: Don't reject reflect-only rotations

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Dec 07, 2016 at 04:54:40PM +0100, Daniel Vetter wrote:
> On Wed, Dec 07, 2016 at 05:13:24PM +0200, Ville Syrjälä wrote:
> > On Wed, Dec 07, 2016 at 03:52:29PM +0100, Daniel Vetter wrote:
> > > On Wed, Dec 07, 2016 at 01:32:57PM +0000, Chris Wilson wrote:
> > > > On Wed, Dec 07, 2016 at 12:18:19PM +0000, Brian Starkey wrote:
> > > > > The check to reject combinations of multiple rotation angles is overly
> > > > > restrictive and has the side-effect of also failing any rotation value
> > > > > which consists only of reflections.
> > > > > 
> > > > > Fix this by relaxing the check to ignore values which contain no
> > > > > rotation flags.
> > > > > 
> > > > > Fixes: 6e0c7c3358d4 ("drm/atomic: Reject attempts to use multiple rotation angles at once")
> > > > > Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> > > > 
> > > > >  drivers/gpu/drm/drm_atomic.c |    3 ++-
> > > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > > > > index 362e3ea..44f4030 100644
> > > > > --- a/drivers/gpu/drm/drm_atomic.c
> > > > > +++ b/drivers/gpu/drm/drm_atomic.c
> > > > > @@ -846,7 +846,8 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
> > > > >  	} else if (property == config->prop_src_h) {
> > > > >  		state->src_h = val;
> > > > >  	} else if (property == plane->rotation_property) {
> > > > > -		if (!is_power_of_2(val & DRM_ROTATE_MASK))
> > > > > +		if ((val & DRM_ROTATE_MASK) &&
> > > > 
> > > > If val & DRM_ROTATE_MASK is zero, val must be REFLECT_X | REFLECT_Y.
> > > 
> > > While we bikeshed this check: Validation like this should be somewhere
> > > behind ->atomic_check, since if it's only here then you can sneak invalid
> > > stuff in through the legacy/compat set_property ioctls.
> > 
> > Not if you use drm_atomic_helper_plane_set_property().
> 
> Oh right, I mixed up the callchain maze in my head again. I still feel
> like putting all the validation code in one place might be a good idea.
> But yeah not strictly needed.

Well, we do quite a bit of checking already earlier. Eg.
drm_property_change_valid(), and obj ID lookups. I think this sort of
"totally invalid use of the API" check fits in pretty well with that
crowd.

-- 
Ville Syrjälä
Intel OTC
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