Re: [PATCH v2 2/2] drm/virtio: Fix host color format for big endian guests

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 20.08.24 um 14:55 schrieb Jocelyn Falempe:
> On 20/08/2024 14:48, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 20.08.24 um 11:07 schrieb Jocelyn Falempe:
>>> The colors are inverted when testing a s390x VM on a s390x host.
>>> Changing the conversion from DRM_FORMAT -> VIRTIO_GPU_FORMAT on big
>>> endian guests fixes the colors. But it may break big-endian guest on
>>> little-endian host. In this case, the fix should be in qemu, because
>>> the host endianess is not known in the guest VM.
>>>
>>> Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
>>> Acked-by: Javier Martinez Canillas <javierm@redhat.com>
>>> ---
>>>   drivers/gpu/drm/virtio/virtgpu_plane.c | 12 ++++++++++--
>>>   1 file changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c 
>>> b/drivers/gpu/drm/virtio/virtgpu_plane.c
>>> index 860b5757ec3fc..0ec6ecc96eb13 100644
>>> --- a/drivers/gpu/drm/virtio/virtgpu_plane.c
>>> +++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
>>> @@ -37,16 +37,24 @@ static const uint32_t 
>>> virtio_gpu_cursor_formats[] = {
>>>       DRM_FORMAT_ARGB8888,
>>>   };
>>> +#ifdef __BIG_ENDIAN
>>> +#define VIRTIO_GPU_HOST_XRGB8888 VIRTIO_GPU_FORMAT_X8R8G8B8_UNORM
>>> +#define VIRTIO_GPU_HOST_ARGB8888 VIRTIO_GPU_FORMAT_A8R8G8B8_UNORM
>>> +#else
>>> +#define VIRTIO_GPU_HOST_XRGB8888 VIRTIO_GPU_FORMAT_B8G8R8X8_UNORM
>>> +#define VIRTIO_GPU_HOST_ARGB8888 VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM
>>> +#endif
>>
>> As these defines are only used here, would it be beneficial to put 
>> the __BIG_ENDIAN branch directly around the switch statement?
>
> That was my first version, but I found it difficult to read, when I 
> mix #ifdef in a switch case.
>
>
> or maybe something like the following would be better ?
>
>
>      switch (drm_fourcc) {
> #ifdef _BIG_ENDIAN
>      case DRM_FORMAT_XRGB8888:
>         format = VIRTIO_GPU_FORMAT_X8R8G8B8_UNORM;
>          break;
>      case DRM_FORMAT_ARGB8888:
>         format = VIRTIO_GPU_FORMAT_A8R8G8B8_UNORM;
>          break;
> #else
>      case DRM_FORMAT_XRGB8888:
>         format = VIRTIO_GPU_FORMAT_B8G8R8X8_UNORM;
>          break;
>      case DRM_FORMAT_ARGB8888:
>         format = VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM;
>          break;
> #endif

I have no preference. Maybe the virtio devs can comment.

Best regards
Thomas

>>
>> Best regards
>> Thomas
>>
>>> +
>>>   uint32_t virtio_gpu_translate_format(uint32_t drm_fourcc)
>>>   {
>>>       uint32_t format;
>>>       switch (drm_fourcc) {
>>>       case DRM_FORMAT_XRGB8888:
>>> -        format = VIRTIO_GPU_FORMAT_B8G8R8X8_UNORM;
>>> +        format = VIRTIO_GPU_HOST_XRGB8888;
>>>           break;
>>>       case DRM_FORMAT_ARGB8888:
>>> -        format = VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM;
>>> +        format = VIRTIO_GPU_HOST_ARGB8888;
>>>           break;
>>>       default:
>>>           /*
>>
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)