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

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 3 Aug 2017 03:17:09 +0000
"Zhang, Tina" <tina.zhang@intel.com> wrote:

> > -----Original Message-----
> > From: dri-devel [mailto:dri-devel-bounces@lists.freedesktop.org] On Behalf Of
> > Alex Williamson
> > Sent: Wednesday, August 2, 2017 5:18 AM
> > To: Zhang, Tina <tina.zhang@intel.com>
> > Cc: Tian, Kevin <kevin.tian@intel.com>; kraxel@redhat.com; intel-
> > gfx@lists.freedesktop.org; Wang, Zhi A <zhi.a.wang@intel.com>;
> > kwankhede@nvidia.com; dri-devel@lists.freedesktop.org; intel-gvt-
> > dev@lists.freedesktop.org; Lv, Zhiyuan <zhiyuan.lv@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@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@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.
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