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

[Zhang, Tina]

> -----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?

Tina