Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation

[Daniel Vetter]

On Wed, Jul 12, 2017 at 02:31:40AM +0000, Zhang, Tina wrote:
> 
> 
> > -----Original Message-----
> > From: intel-gvt-dev [mailto:intel-gvt-dev-bounces@xxxxxxxxxxxxxxxxxxxxx] On
> > Behalf Of Daniel Vetter
> > Sent: Tuesday, July 11, 2017 5:13 PM
> > To: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> > Cc: Tian, Kevin <kevin.tian@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; intel-
> > gfx@xxxxxxxxxxxxxxxxxxxxx; alex.williamson@xxxxxxxxxx;
> > zhenyuw@xxxxxxxxxxxxxxx; chris@xxxxxxxxxxxxxxxxxx; Kirti Wankhede
> > <kwankhede@xxxxxxxxxx>; Lv, Zhiyuan <zhiyuan.lv@xxxxxxxxx>;
> > daniel@xxxxxxxx; Zhang, Tina <tina.zhang@xxxxxxxxx>; intel-gvt-
> > dev@xxxxxxxxxxxxxxxxxxxxx; Wang, Zhi A <zhi.a.wang@xxxxxxxxx>
> > Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation
> > 
> > On Tue, Jul 11, 2017 at 08:14:08AM +0200, Gerd Hoffmann wrote:
> > >   Hi,
> > >
> > > > > +struct vfio_device_query_gfx_plane {
> > > > > +	__u32 argsz;
> > > > > +	__u32 flags;
> > > > > +	struct vfio_device_gfx_plane_info plane_info;
> > > > > +	__u32 plane_type;
> > > > > +	__s32 fd; /* dma-buf fd */
> > > > > +	__u32 plane_id;
> > > > > +};
> > > > > +
> > > >
> > > > It would be better to have comment here about what are expected
> > > > values for plane_type and plane_id.
> > >
> > > plane_type is DRM_PLANE_TYPE_*.
> > >
> > > yes, a comment saying so would be good, same for drm_format which is
> > > DRM_FORMAT_*.  While looking at these two: renaming plane_type to
> > > drm_plane_type (for consistency) is probably a good idea too.
> > >
> > > plane_id needs a specification.
> > 
> > Why do you need plane_type? With universal planes the plane_id along is
> > sufficient to identify a plane on a given drm device instance. I'd just remove it.
> > -Daniel
> The plane_type here, is to ask the mdev vendor driver to return the information according to the value in field plane_type. So, it's a input field.
> The values in plane_type field is the same of drm_plane_type. And yes, it's better to use drm_plane_type instead of plane_id. 

I have no idea what you mean here, I guess that just shows that discussing
an ioctl struct without solid definitions of what field does what and why
is not all that useful. What exactly it plane_id for then?

This just confused me more ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch