On Wed, Jan 10, 2024 at 05:56:28PM +0800, Julia Zhang wrote:
> drm_gem_map_attach() requires drm_gem_object_funcs.get_sg_table to be
> implemented, or else return ENOSYS. Virtio has no get_sg_table
> implemented for vram object. To fix this, add a new device_attach to
> call drm_gem_map_attach() for shmem object and return 0 for vram object
> instead of calling drm_gem_map_attach for both of these two kinds of
> object.
>
> Signed-off-by: Julia Zhang <julia.zhang@xxxxxxx>
> ---
> drivers/gpu/drm/virtio/virtgpu_prime.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c b/drivers/gpu/drm/virtio/virtgpu_prime.c
> index 44425f20d91a..f0b0ff6f3813 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_prime.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_prime.c
> @@ -71,6 +71,18 @@ static void virtgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
> drm_gem_unmap_dma_buf(attach, sgt, dir);
> }
>
> +static int virtgpu_gem_device_attach(struct dma_buf *dma_buf,
> + struct dma_buf_attachment *attach)
> +{
> + struct drm_gem_object *obj = attach->dmabuf->priv;
> + struct virtio_gpu_object *bo = gem_to_virtio_gpu_obj(obj);
> +
> + if (virtio_gpu_is_vram(bo))
> + return 0;
You need to reject attach here because these vram buffer objects cannot be
used by any other driver. In that case dma_buf_attach _must_ fail, not
silently succeed.
Because if it silently succeeds then the subsequent dma_buf_map_attachment
will blow up because you don't have the ->get_sg_table hook implemented.
Per the documentation the error code for this case must be -EBUSY, see the
section for the attach hook here:
https://dri.freedesktop.org/docs/drm/driver-api/dma-buf.html#c.dma_buf_ops
Since you're looking into this area, please make sure there's not other
similar mistake in virtio code.
Also can you please make a kerneldoc patch for struct virtio_dma_buf_ops
to improve the documentation there? I think it would be good to move those
to the inline style and then at least put a kernel-doc hyperlink to struct
dma_buf_ops.attach and mention that attach must fail for non-shareable
buffers.
In general the virtio_dma_buf kerneldoc seems to be on the "too minimal,
explains nothing" side of things :-/
Cheers, Sima
> +
> + return drm_gem_map_attach(dma_buf, attach);
> +}
> +
> static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops = {
> .ops = {
> .cache_sgt_mapping = true,
> @@ -83,7 +95,7 @@ static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops = {
> .vmap = drm_gem_dmabuf_vmap,
> .vunmap = drm_gem_dmabuf_vunmap,
> },
> - .device_attach = drm_gem_map_attach,
> + .device_attach = virtgpu_gem_device_attach,
> .get_uuid = virtgpu_virtio_get_uuid,
> };
>
> --
> 2.34.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
