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

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Date:   Mon, 19 Jun 2017 08:34:13 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>
Cc:     Xiaoguang Chen <xiaoguang.chen@...el.com>,
        chris@...is-wilson.co.uk, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, zhenyuw@...ux.intel.com,
        zhiyuan.lv@...el.com, intel-gvt-dev@...ts.freedesktop.org,
        zhi.a.wang@...el.com, kevin.tian@...el.com
Subject: Re: [PATCH v9 5/7] vfio: Define vfio based dma-buf operations

  Hi,

> So perhaps this becomes:
> 
> 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;
> };

Looks good.

> 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; 
> };

Hmm, plane isn't really an ID, it is a type, with type being either
DRM_PLANE_TYPE_PRIMARY or DRM_PLANE_TYPE_CURSOR, so I don't think the
flage above make sense.

What are the nvidia plane for cursor support btw?

> The flag defines the data in the id field as either referring to a
> region (perhaps there could be multiple regions with only one active)

Well, we have a "start" field in vfio_device_gfx_plane_info (maybe we
should rename that to "offset"), which can be used to place multiple
planes into a single, fixed region.

Also I think it would be useful to have some way to figure the device
capabilities as the userspace workflow will look quite different for
the two cases.

cheers,
  Gerd