Re: [PATCH v16 5/6] vfio: ABI for mdev display dma-buf operation

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> +/**
> + * VFIO_DEVICE_QUERY_GFX_PLANE - _IOW(VFIO_TYPE, VFIO_BASE + 14,
> + *                                    struct
> vfio_device_query_gfx_plane)
> + *
> + * Set the drm_plane_type and flags, then retrieve the gfx plane
> info.
> + *
> + * flags supported:
> + * - VFIO_GFX_PLANE_TYPE_PROBE and VFIO_GFX_PLANE_TYPE_DMABUF are
> set
> + *   to ask if the mdev supports dma-buf. 0 on support, -EINVAL on
> no
> + *   support for dma-buf.
> + * - VFIO_GFX_PLANE_TYPE_PROBE and VFIO_GFX_PLANE_TYPE_REGION are
> set
> + *   to ask if the mdev supports region. 0 on support, -EINVAL on no
> + *   support for region.
> + * - VFIO_GFX_PLANE_TYPE_DMABUF or VFIO_GFX_PLANE_TYPE_REGION is set
> + *   with each call to query the plane info.
> + * - Others are invalid and return -EINVAL.
> + *
> + * Return: 0 on success, -ENODEV with all out fields zero on mdev
> + * device initialization, -errno on other failure.

Should also not here that it is not an error if the guest has not
defined a plane yet.  The ioctl should return success in that case and
zero-initialize plane info (drm_format + size + width + height fields).

> + */
> +struct vfio_device_gfx_plane_info {
> +	__u32 argsz;
> +	__u32 flags;
> +#define VFIO_GFX_PLANE_TYPE_PROBE (1 << 0)
> +#define VFIO_GFX_PLANE_TYPE_DMABUF (1 << 1)
> +#define VFIO_GFX_PLANE_TYPE_REGION (1 << 2)
> +	/* in */
> +	__u32 drm_plane_type;	/* type of plane: 
> DRM_PLANE_TYPE_* */

Add a head field here?  People asked @ kvm forum about multihead
support.  Even if the initial driver version doesn't support it we
could add a field so it becomes easier to add it at some point in the
future.

Probing for available heads could be done with the PROBE flag, i.e.
flags = PROBE | DMABUF, plane_type = PRIMARY, head = 0, 1, ...

> +	__u32 x_hot;    /* horizontal position of cursor hotspot */
> +	__u32 y_hot;    /* vertical position of cursor hotspot */

Needs documentation how the driver signals "no hotspot information
available" (using 0xffffffff for example).

cheers,
  Gerd