[PATCH v13 5/7] vfio: ABI for mdev display dma-buf operation

[Zhang, Tina]

> -----Original Message-----
> From: dri-devel [mailto:dri-devel-bounces at lists.freedesktop.org] On Behalf Of
> Alex Williamson
> Sent: Thursday, August 3, 2017 10:43 PM
> To: Zhang, Tina <tina.zhang at intel.com>
> Cc: Tian, Kevin <kevin.tian at intel.com>; intel-gfx at lists.freedesktop.org; dri-
> devel at lists.freedesktop.org; kwankhede at nvidia.com; kraxel at redhat.com;
> intel-gvt-dev at lists.freedesktop.org; Wang, Zhi A <zhi.a.wang at intel.com>; Lv,
> Zhiyuan <zhiyuan.lv at intel.com>
> Subject: Re: [PATCH v13 5/7] vfio: ABI for mdev display dma-buf operation
> 
> On Thu, 3 Aug 2017 07:08:15 +0000
> "Zhang, Tina" <tina.zhang at intel.com> wrote:
> 
> > > -----Original Message-----
> > > From: Alex Williamson [mailto:alex.williamson at redhat.com]
> > > Sent: Thursday, August 3, 2017 11:38 AM
> > > To: Zhang, Tina <tina.zhang at intel.com>
> > > Cc: Tian, Kevin <kevin.tian at intel.com>;
> > > intel-gfx at lists.freedesktop.org; dri- devel at lists.freedesktop.org;
> > > kwankhede at nvidia.com; kraxel at redhat.com;
> > > intel-gvt-dev at lists.freedesktop.org; Wang, Zhi A
> > > <zhi.a.wang at intel.com>; Lv, Zhiyuan <zhiyuan.lv at intel.com>
> > > Subject: Re: [PATCH v13 5/7] vfio: ABI for mdev display dma-buf
> > > operation
> > >
> > > On Thu, 3 Aug 2017 03:17:09 +0000
> > > "Zhang, Tina" <tina.zhang at intel.com> wrote:
> > >
> > > > > -----Original Message-----
> > > > > From: dri-devel [mailto:dri-devel-bounces at lists.freedesktop.org]
> > > > > On Behalf Of Alex Williamson
> > > > > Sent: Wednesday, August 2, 2017 5:18 AM
> > > > > To: Zhang, Tina <tina.zhang at intel.com>
> > > > > Cc: Tian, Kevin <kevin.tian at intel.com>; kraxel at redhat.com;
> > > > > intel- gfx at lists.freedesktop.org; Wang, Zhi A
> > > > > <zhi.a.wang at intel.com>; kwankhede at nvidia.com;
> > > > > dri-devel at lists.freedesktop.org; intel-gvt-
> > > > > dev at lists.freedesktop.org; Lv, Zhiyuan <zhiyuan.lv at intel.com>
> > > > > Subject: Re: [PATCH v13 5/7] vfio: ABI for mdev display dma-buf
> > > > > operation
> > > > >
> > > > > On Tue, 25 Jul 2017 17:28:18 +0800 Tina Zhang
> > > > > <tina.zhang at intel.com> wrote:
> > > > >
> > > > > > Add VFIO_DEVICE_QUERY_GFX_PLANE ioctl command to let user
> mode
> > > > > > query and get the plan and its related information.
> > > > > >
> > > > > > The dma-buf's life cycle is handled by user mode and tracked by kernel.
> > > > > > The returned fd in struct vfio_device_query_gfx_plane can be a
> > > > > > new fd or an old fd of a re-exported dma-buf. Host User mode
> > > > > > can check the value of fd and to see if it needs to create new
> > > > > > resource according to the new fd or just use the existed
> > > > > > resource related to the old
> > > fd.
> > > > > >
> > > > > > Signed-off-by: Tina Zhang <tina.zhang at intel.com>
> > > > > > ---
> > > > > >  include/uapi/linux/vfio.h | 28 ++++++++++++++++++++++++++++
> > > > > >  1 file changed, 28 insertions(+)
> > > > > >
> > > > > > diff --git a/include/uapi/linux/vfio.h
> > > > > > b/include/uapi/linux/vfio.h index ae46105..827a230 100644
> > > > > > --- a/include/uapi/linux/vfio.h
> > > > > > +++ b/include/uapi/linux/vfio.h
> > > > > > @@ -502,6 +502,34 @@ struct vfio_pci_hot_reset {
> > > > > >
> > > > > >  #define VFIO_DEVICE_PCI_HOT_RESET	_IO(VFIO_TYPE, VFIO_BASE +
> > > > > 13)
> > > > > >
> > > > > > +/**
> > > > > > + * VFIO_DEVICE_QUERY_GFX_PLANE - _IOW(VFIO_TYPE, VFIO_BASE
> +
> > > 14,
> > > > > > +struct vfio_device_query_gfx_plane)
> > > > > > + *
> > > > > > + * Set the drm_plane_type and retrieve information about the gfx
> plane.
> > > > > > + *
> > > > > > + * Return: 0 on success, -errno on failure.
> > > > > > + */
> > > > > > +struct vfio_device_gfx_plane_info {
> > > > > > +	__u32 argsz;
> > > > > > +	__u32 flags;
> > > > > > +	/* in */
> > > > > > +	__u32 drm_plane_type;	/* type of plane: DRM_PLANE_TYPE_*
> */
> > > > > > +	/* out */
> > > > > > +	__u32 drm_format;	/* drm format of plane */
> > > > > > +	__u64 drm_format_mod;   /* tiled mode */
> > > > > > +	__u32 width;	/* width of plane */
> > > > > > +	__u32 height;	/* height of plane */
> > > > > > +	__u32 stride;	/* stride of plane */
> > > > > > +	__u32 size;	/* size of plane in bytes, align on page*/
> > > > > > +	__u32 x_pos;	/* horizontal position of cursor plane, upper
> left corner
> > > > > in pixels */
> > > > > > +	__u32 y_pos;	/* vertical position of cursor plane, upper left
> corner in
> > > > > lines*/
> > > > > > +	__u32 region_index;
> > > > > > +	__s32 fd;	/* dma-buf fd */
> > > > >
> > > > > How do I know which of these is valid, region_index or fd?  Can
> > > > > I ask for one vs the other?  What are the errno values to
> > > > > differentiate unsupported vs not initialized?  Is there a "probe"
> > > > > flag that I can use to determine what the device supports
> > > > > without allocating
> > > those resources yet?
> > > > Dma-buf won't use region_index, which means region_index is zero
> > > > all the
> > > time for dma-buf usage.
> > > > As we discussed, there won't be errno if not initialized, just keep all fields
> zero.
> > > > I will add the comments about these in the next version. Thanks
> > >
> > > Zero is a valid region index.
> > If zero is valid, can we find out other invalid value? How about 0xffffffff?
> 
> Unlikely, but also valid.  Isn't this why we have a flags field in the structure, so
> we don't need to rely on implicit values as invalid.
> Also, all of the previously discussed usage models needs to be documented,
> either here in the header or in a Documentation/ file.
According to the previously discussion, we also have the following propose:
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;
};
So, we may need to add one more ioctl, e.g. VFIO_DEVICE_QUERY_GFX_CAPS.
User mode can query this before querying the plan info, and to see which usage
(dma-buf or region) is supported.
Does it still make sense?
Thanks.

Tina


> Thanks,
> 
> Alex
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