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

[Dmitry Osipenko <dmitry.osipenko@collabora.com>]

On 10/1/26 16:31, Thomas Zimmermann wrote:
> 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@redhat.com>
>>>> ---
>>>>    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.

Chances are low this may ever become necessary. Confirm glmark2-drm now
works with this change.

Applied to misc-next

-- 
Best regards,
Dmitry