[PATCH 2/3] drm/vc4: Force ->x_scaling[1] should never be set to VC4_SCALING_NONE

[Boris Brezillon]

On Thu, 08 Nov 2018 06:52:44 -0800
Eric Anholt <eric at anholt.net> wrote:

> Boris Brezillon <boris.brezillon at bootlin.com> writes:
> 
> > For the YUV conversion to work properly, ->x_scaling[0,1] should never
> > be set to VC4_SCALING_NONE, but vc4_get_scaling_mode() might return
> > VC4_SCALING_NONE if the horizontal scaling ratio exactly matches the
> > horizontal subsampling factor. Add a test to turn VC4_SCALING_NONE
> > into VC4_SCALING_PPF when that happens.
> >
> > Fixes: fc04023fafec ("drm/vc4: Add support for YUV planes.")
> > Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>  
> 
> I couldn't find a spec justification for this -- did you have a testcase
> that fails?

Yep. Just set the downscaling ratio to 0.5 with an NV12 format and
you'll hit the issue (I used modetest to do that):

# modetest -M vc4 -s 29:1920x1080-60  -P 96 at 95:1920x1080*0.5 at NV12