Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations

From: Gerd Hoffmann
Date: Tue Jun 20 2017 - 06:57:31 EST

On Tue, 2017-06-20 at 08:41 +0000, Zhang, Tina wrote:
> Hi,
> Thanks for all the comments. Here are the summaries:
> 1. Modify the structures to make it more general.
> struct vfio_device_gfx_plane_info {
> __u64 start;
> __u64 drm_format_mod;
> __u32 drm_format;
> __u32 width;
> __u32 height;
> __u32 stride;
> __u32 size;
> __u32 x_pos;
> __u32 y_pos;
> __u32 generation;
> };

Looks good to me.

> struct vfio_device_query_gfx_plane {
> __u32 argsz;
> __u32 flags;
> #define VFIO_GFX_PLANE_FLAGS_PLANE_ID (1 << 1)
> struct vfio_device_gfx_plane_info plane_info;
> __u32 id;Â
> };

I'm not convinced the flags are a great idea. Whenever dmabufs or a
region is used is a static property of the device, not of each
individual plane.

I think we should have this for userspace to figure:

enum vfio_device_gfx_type {

struct vfio_device_gfx_query_caps {
__u32 argsz;
__u32 flags;
enum vfio_device_gfx_type;

Then this to query the plane:

struct vfio_device_gfx_query_plane {
__u32 argsz;
__u32 flags;
struct vfio_device_gfx_plane_info plane_info; /* out */
__u32 plane_type; /* in */

2. Remove dmabuf mgr fd and add these two ioctl commands to the vfio
device fd.
> vfio_device_gfx_plane_info.


> VFIO_DEVICE_GET_DMABUF_FD: used to create and return the dmabuf fd.

Yes. The plane might have changed between query-plane and get-dmabuf
ioctl calls though, we must make sure we handle that somehow. Current
patches return plane_info on get-dmabuf ioctl too, so userspace can see
what it actually got.

With the generation we can also do something different: Pass in
plane_type and generation, and have VFIO_DEVICE_GET_DMABUF_FD return
an error in case the generation doesn't match. In that case it doesn't
make much sense any more to have a separate plane_info struct, which
was added so we don't have to duplicate things in query-plane and get-
dmabuf ioctl structs.