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SubjectRE: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf operations
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> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel@redhat.com]
> Sent: Tuesday, June 20, 2017 6:58 PM
> To: Zhang, Tina <tina.zhang@intel.com>; Alex Williamson
> <alex.williamson@redhat.com>
> Cc: intel-gfx@lists.freedesktop.org; linux-kernel@vger.kernel.org; Kirti
> Wankhede <kwankhede@nvidia.com>; Chen, Xiaoguang
> <xiaoguang.chen@intel.com>; intel-gvt-dev@lists.freedesktop.org; Lv, Zhiyuan
> <zhiyuan.lv@intel.com>; Wang, Zhi A <zhi.a.wang@intel.com>; Wang, Zhenyu
> Z <zhenyu.z.wang@intel.com>
> Subject: Re: [Intel-gfx] [PATCH v9 5/7] vfio: Define vfio based dma-buf
> operations
>
> 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_REGION_ID (1 << 0)
> > #define VFIO_GFX_PLANE_FLAGS_PLANE_ID (1 << 1)
> > struct vfio_device_gfx_plane_info plane_info;
> > __u32 id;
> > };
>
> 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 {
> VFIO_DEVICE_GFX_NONE,
> VFIO_DEVICE_GFX_DMABUF,
> VFIO_DEVICE_GFX_REGION,
> };
>
> 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_QUERY_GFX_PLANE : used to query
> > vfio_device_gfx_plane_info.
>
> Yes.
>
> > 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.
Comparing with the current patch, this would make user space a little bit harder to
get the dmabuf by calling VFIO_DEVICE_GET_DMABUF ioctl. Is it efficient for
user mode usage?

Thanks
Tina
>
> cheers,
> Gerd

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