Re: [PATCH] drm/virtio: add ARGB8888 support for primary planes

[Thomas Zimmermann]

Hi

Am 01.10.26 um 12:46 schrieb Dmitry Osipenko:
> On 9/30/26 18:03, Thomas Zimmermann wrote:
> > Hi
> >
> > Am 30.09.26 um 15:27 schrieb Dorinda Bassey:
> > > Add DRM_FORMAT_HOST_ARGB8888 to the list of supported formats for
> > > virtio-gpu primary planes. Without this, glmark2-drm fails at
> > > startup because it selects ARGB visual configs by default, which
> > > don't match the XRGB-only plane capabilities. This causes
> > > drmModeSetCrtc to fail with EINVAL.
> > But does the host also support ARGB on the primary plane? We usually
> > don't export formats that are not available in (virtual) hardware.
> >
> > Best regards
> > Thomas
> >
> > > The virtio_gpu_translate_format() function already handles
> > > ARGB8888 translation to VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM,
> > > so this just exposes the existing capability to userspace.
> > >
> > > Signed-off-by: Dorinda Bassey <dbassey@xxxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/virtio/virtgpu_plane.c | 1 +
> > >    1 file changed, 1 insertion(+)
> For primary plane, alpha channel often doesn't matter as primary has
> fixed z=0 order and a usual alpha blending mode would account only
> overlay's alpha channel. Many real hw drivers expose alpha-channel
> formats for primary plane for compatibility with userspace, even though
> for them the alpha has no meaning for the primary plane.

We decidedly do not offer formats that are not native to the hardware; 
except for adding XRGB888.


> QEMU is most popular VMM using virtio-gpu, but there are others. For a
> stricter compatibility we can translate B8G8R8A8 to X8R8G8B8 for the
> primary plane in the driver code, but I assume in practice it's very
> unlike this will be necessary and we can always do it later on if will
> be needed.

No in-kernel format conversion please; again except for adding XRGB8888.

Best regards
Thomas


> The change looks okay, will apply after testing.

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)