Re: [PATCH 2/3] drm: Make sure at least one plane supports the fb format

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

On Thu, Mar 15, 2018 at 10:42:17AM -0700, Eric Anholt wrote:
> Ville Syrjala <ville.syrjala@linux.intel.com> writes:
> 
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > To make life easier for drivers, let's have the core check that the
> > requested pixel format is supported by at least one plane when creating
> > a new framebuffer.
> >
> > This eases the burden on drivers by making sure they'll never get
> > requests to create fbs with unsupported pixel formats. Thanks to the
> > new .fb_modifier() hook this check can now be done whether the request
> > specifies the modifier directly or driver has to deduce it from the
> > gem bo tiling (or via any other method really).
> >
> > v0: Accept anyformat if the driver doesn't do planes (Eric)
> >     s/planes_have_format/any_plane_has_format/ (Eric)
> >     Check the modifier as well since we already have a function
> >     that does both
> > v3: Don't do the check in the core since we may not know the
> >     modifier yet, instead export the function and let drivers
> >     call it themselves
> > v4: Unexport the functiona and put the format_default check back
> >     since this will again be called by the core, ie. undo v3 ;)
> >
> > Cc: Eric Anholt <eric@anholt.net>
> > Testcase: igt/kms_addfb_basic/expected-formats
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/drm_framebuffer.c | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
> > index 21d3d51eb261..e618a6b728d4 100644
> > --- a/drivers/gpu/drm/drm_framebuffer.c
> > +++ b/drivers/gpu/drm/drm_framebuffer.c
> > @@ -152,6 +152,26 @@ static int fb_plane_height(int height,
> >  	return DIV_ROUND_UP(height, format->vsub);
> >  }
> >  
> > +static bool any_plane_has_format(struct drm_device *dev,
> > +				 u32 format, u64 modifier)
> > +{
> > +	struct drm_plane *plane;
> > +
> > +	drm_for_each_plane(plane, dev) {
> > +		/*
> > +		 * In case the driver doesn't really do
> > +		 * planes we have to accept any format here.
> > +		 */
> > +		if (plane->format_default)
> > +			return true;
> > +
> > +		if (drm_plane_check_pixel_format(plane, format, modifier) == 0)
> > +			return true;
> > +	}
> > +
> > +	return false;
> > +}
> 
> This drm_plane_check_pixel_format() will always fail for VC4's SAND
> modifiers or VC5's UIF modifiers, where we're using the middle 48 bits
> as a bit of metadata (like how we have horizontal stride passed outside
> of the modifier) and you can't list all of the possible values in an
> array on the plane.

Hmm. drm_atomic_plane_check() etc. call this thing as well. How does
that manage to work currently?

-- 
Ville Syrjälä
Intel OTC
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