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

[Daniel Vetter]

On Tue, Feb 23, 2021 at 7:50 PM Daniel Stone <daniel at fooishbar.org> wrote:
>
> 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.

That sounds a bit like userspace being too simple. Since if they're ok
with dealing with modifiers accessing the raw buffer is out the window
anyway, so bgr vs rgb shouldn't matter.

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

But also this ofc.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch