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 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?

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)