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

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Message-ID: <1497956256.16795.7.camel@redhat.com>
Date:   Tue, 20 Jun 2017 12:57:36 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     "Zhang, Tina" <tina.zhang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Chen, Xiaoguang" <xiaoguang.chen@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Lv, Zhiyuan" <zhiyuan.lv@...el.com>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        "Wang, Zhenyu Z" <zhenyu.z.wang@...el.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.

cheers,
  Gerd