[PATCH xserver] dri3: Fix DRI3.2 support for drivers other than modesetting-ddx.

[Daniel Stone]

Hi Mario,

On 24 April 2018 at 09:17, Mario Kleiner <mario.kleiner.de at gmail.com> wrote:
> Both xf86-video-intel and xf86-video-nouveau cause OpenGL
> clients to fail when used with DRI3 on server 1.20 with Mesa 18.1.
>
> Reason is that the servers DRI3 version is now unconditionally
> reported as DRI3 1.2 to 1.2 capable clients. This causes clients
> using Mesa 18.1 to use the new DRI 3.2 requests DRI3GetSupportedModifiers,
> DRI3PixmapFromBuffers, etc. Drivers other than modesetting-ddx
> do not support the needed hooks like info->pixmap_from_fds or
> info->get_formats, info->get_modifiers. Unfortunately we can't
> simply report the servers DRI3 version as 1.0 in this case, as
> the reported version can not be specific to a X-Screen, and
> different screens may have drivers with different capabilities.

Thanks a lot for hunting this down! This fix does still make me
uncomfortable though. I think a better fix would be, on the Mesa side,
to never call any 1.2 codepaths for the server if we get no
formats/modifiers back from the GetSupported calls, and to never call
any 1.2 codepaths for the drawable if DRIImage's
createImageWithModifiers does not exist or if it fails and we fall
back to regular createImage. That way we make sure that both sides
exercise the same behaviour: either both with explicit modifiers, or
neither.

Cheers,
Daniel