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

[Daniel Stone]

Hi Brian,

On Tue, 23 Feb 2021 at 18:34, Brian Starkey <brian.starkey at arm.com> wrote:
> On Tue, Feb 23, 2021 at 05:10:16PM +0000, Alyssa Rosenzweig wrote:
> > But it seems to me allowing
> > both BGR+YTR and RGB+YTR upstream is the better route than simply
> > preventing hardware from using AFBC at all, and there are natural
> > encodings for both with fourcc modifiers.
>
> Are those the only options? I see XBGR8888, ABGR8888, BGR888 and
> BGR565 are all handled in vop_convert_afbc_format(), which are all
> "valid" for use with YTR, and all except XBGR are on the "preferred"
> AFBC format list in afbc.rst.

The issue is a userspace one though, not a kernel one. Userspace (e.g.
GNOME Shell, Weston, Xorg) decides ahead of time that it's going to
use XRGB8888, then use the modifiers available to it for that format.
There's no logic in those projects to look at the list of 8bpc
non-alpha formats, examine XRGB vs. XBGR, decide that XBGR is 'better'
since it has more modifiers available, then go use XBGR.

So whilst removing XRGB+AFBC wouldn't technically remove the
possibility to use AFBC, the practical effect is that it wouldn't be
used.

Cheers,
Daniel