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

[Gerd Hoffmann]

On Tue, Aug 20, 2024 at 11:07:41AM GMT, Jocelyn Falempe wrote:
> 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 at redhat.com>
> Acked-by: Javier Martinez Canillas <javierm at 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

VIRTIO_GPU_FORMAT_* is little endian (like DRM_FORMAT_*), there should
be no need to do anything byte order specific here.  This looks like you
are papering over a bug somewhere else.

take care,
  Gerd