Boris Brezillon <boris.brezillon@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@bootlin.com>

I couldn't find a spec justification for this -- did you have a testcase
that fails?