Re: [PATCH for-8.1] vfio/display: Fix missing update to set backing fields

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 16/8/23 23:55, Alex Williamson wrote:
> The below referenced commit renames scanout_width/height to
> backing_width/height, but also promotes these fields in various portions
> of the egl interface.  Meanwhile vfio dmabuf support has never used the
> previous scanout fields and is therefore missed in the update.  This
> results in a black screen when transitioning from ramfb to dmabuf display
> when using Intel vGPU with these features.

Referenced commit isn't trivial. Maybe because it is too late here.
I'd have tried to split it. Anyhow, too late (again).

Is vhost-user-gpu also affected? (see VHOST_USER_GPU_DMABUF_SCANOUT
in vhost_user_gpu_handle_display()).

> Link: https://lists.gnu.org/archive/html/qemu-devel/2023-08/msg02726.html
> Fixes: 9ac06df8b684 ("virtio-gpu-udmabuf: correct naming of QemuDmaBuf size properties")
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> 
> This fixes a regression in dmabuf/EGL support for Intel GVT-g and
> potentially the mbochs mdev driver as well.  Once validated by those
> that understand dmabuf/EGL integration, I'd welcome QEMU maintainers to
> take this directly for v8.1 or queue it as soon as possible for v8.1.1.
> 
>   hw/vfio/display.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/hw/vfio/display.c b/hw/vfio/display.c
> index bec864f482f4..837d9e6a309e 100644
> --- a/hw/vfio/display.c
> +++ b/hw/vfio/display.c
> @@ -243,6 +243,8 @@ static VFIODMABuf *vfio_display_get_dmabuf(VFIOPCIDevice *vdev,
>       dmabuf->dmabuf_id  = plane.dmabuf_id;
>       dmabuf->buf.width  = plane.width;
>       dmabuf->buf.height = plane.height;
> +    dmabuf->buf.backing_width = plane.width;
> +    dmabuf->buf.backing_height = plane.height;
>       dmabuf->buf.stride = plane.stride;
>       dmabuf->buf.fourcc = plane.drm_format;
>       dmabuf->buf.modifier = plane.drm_format_mod;