[PATCH] drm/rockchip: Require the YTR modifier for AFBC

[Daniel Stone]

On Tue, 23 Feb 2021 at 14:58, Brian Starkey <brian.starkey at arm.com> wrote:
> On Tue, Feb 23, 2021 at 02:27:11PM +0000, Daniel Stone wrote:
> > Mark, or others from Rockchip, can you please:
> > - explain if there is a way to enable/disable the YTR transform in the
> > VOP's AFBC decoder, similar to the split-block control bit?
> > - ack this patch which correctly declares that the YTR transform is in
> > use in order to make Panfrost work, so it can be merged through
> > drm-misc, or provide another solution which fixes this API mistake?
> > - if VOP does have a hidden YTR-disable bit, add support to disable
> > YTR so rockchip-drm can continue advertising the non-YTR modifier, and
> > Cc this patch for backporting to every kernel tree which declares AFBC
> > modifier support?
>
> Drive-by $0.02:
>
> As described in https://www.kernel.org/doc/Documentation/gpu/afbc.rst,
> YTR is only valid for "BGR" component order, so this shouldn't be set
> or used for "RGB" order (or YUV) formats. For BGR-order formats, it's
> best to always enable YTR to get the best compression ratio.
>
> In an ideal world, there wouldn't be hardware/drivers which
> support/allow non-standard encodings, but we don't live in that world
> :-(

This implies that RGB component ordering cannot be used together with
AFBC on RK3399, no?

Cheers,
Daniel