Re: [PATCH v13 5/7] vfio: ABI for mdev display dma-buf operation

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 25 Jul 2017 17:28:18 +0800
Tina Zhang <tina.zhang@intel.com> wrote:

> Add VFIO_DEVICE_QUERY_GFX_PLANE ioctl command to let user mode query and
> get the plan and its related information.
> 
> The dma-buf's life cycle is handled by user mode and tracked by kernel.
> The returned fd in struct vfio_device_query_gfx_plane can be a new
> fd or an old fd of a re-exported dma-buf. Host User mode can check the
> value of fd and to see if it needs to create new resource according to
> the new fd or just use the existed resource related to the old fd.
> 
> Signed-off-by: Tina Zhang <tina.zhang@intel.com>
> ---
>  include/uapi/linux/vfio.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ae46105..827a230 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -502,6 +502,34 @@ struct vfio_pci_hot_reset {
>  
>  #define VFIO_DEVICE_PCI_HOT_RESET	_IO(VFIO_TYPE, VFIO_BASE + 13)
>  
> +/**
> + * VFIO_DEVICE_QUERY_GFX_PLANE - _IOW(VFIO_TYPE, VFIO_BASE + 14, struct vfio_device_query_gfx_plane)
> + *
> + * Set the drm_plane_type and retrieve information about the gfx plane.
> + *
> + * Return: 0 on success, -errno on failure.
> + */
> +struct vfio_device_gfx_plane_info {
> +	__u32 argsz;
> +	__u32 flags;
> +	/* in */
> +	__u32 drm_plane_type;	/* type of plane: DRM_PLANE_TYPE_* */
> +	/* out */
> +	__u32 drm_format;	/* drm format of plane */
> +	__u64 drm_format_mod;   /* tiled mode */
> +	__u32 width;	/* width of plane */
> +	__u32 height;	/* height of plane */
> +	__u32 stride;	/* stride of plane */
> +	__u32 size;	/* size of plane in bytes, align on page*/
> +	__u32 x_pos;	/* horizontal position of cursor plane, upper left corner in pixels */
> +	__u32 y_pos;	/* vertical position of cursor plane, upper left corner in lines*/
> +	__u32 region_index;
> +	__s32 fd;	/* dma-buf fd */

How do I know which of these is valid, region_index or fd?  Can I ask
for one vs the other?  What are the errno values to differentiate
unsupported vs not initialized?  Is there a "probe" flag that I can use
to determine what the device supports without allocating those
resources yet?

Kirti, does this otherwise meet your needs?

Thanks,
Alex
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