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

[Thomas Zimmermann]

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 <jfale...@redhat.com>
Acked-by: Javier Martinez Canillas <javi...@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)