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

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Date:   Wed, 21 Jun 2017 13:03:31 +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 Wed, 2017-06-21 at 09:20 +0000, Zhang, Tina wrote:
> Thanks for all the comments. I'm planning to cook the next version of
> this patch set

How about posting only this patch instead of the whole series until
we've settled the interfaces?

> Could the following two works?
> #define VFIO_DEVICE_FLAGS_DMABUF  (1 << 5)        /* vfio-dmabuf
> device */

VFIO_DEVICE_FLAGS_GFX_DMABUF?

> 2. vfio_device_gfx_plane_info
> struct vfio_device_gfx_plane_info {
> 	__u64 start;-> offset
> 	__u64 drm_format_mod;
> 	__u32 drm_format;
> 	__u32 width;
> 	__u32 height;
> 	__u32 stride;
> 	__u32 size;
> 	__u32 x_pos;
> 	__u32 y_pos;
> };
> > Does it make sense to have a "generation" field in the plane_info
> > struct (which gets increased each time the struct changes) ?

> Well,  Gerd, can you share more details about how to use this field
> in user mode, so that we can figure out a way to support it? Thanks.

generation would be increased each time one of the fields in
vfio_device_gfx_plane_info changes, typically on mode switches
(width/height changes) and pageflips (offset changes).  So userspace
can simply compare generation instead of comparing every field to
figure whenever something changed compared to the previous poll.

> 
> 3. vfio_device_query_gfx_plane
> 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;
> 	__u32 plane_type;
> };
> So far, dmabuf use id for DRM_PLANE_TYPE_PRIMARY or
> DRM_PLANE_TYPE_CURSOR.


>  If the newly added plane_type is used for this, the id field may be
> useless in dmabuf usage. Do you have any idea about the usage of this
> id field in dmabuf usage?

plane_type should be DRM_PLANE_TYPE_PRIMARY or DRM_PLANE_TYPE_CURSOR
for dmabuf.

Given that nvidia doesn't support a separate cursor plane in their
region they would support DRM_PLANE_TYPE_PRIMARY only.

I can't see yet what id would be useful for.

Likewise I can't see yet what the VFIO_GFX_PLANE_FLAGS_* are good for.

cheers,
  Gerd