Re: [PATCH 1/3] vfio-ccw: add capabilities chain

Cornelia Huck
2018-12-21T11:12:02Z

On Wed, 19 Dec 2018 09:28:00 -0700
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Tue, 18 Dec 2018 18:24:00 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
>
> > On Mon, 17 Dec 2018 16:53:34 -0500
> > Eric Farman <farman@linux.ibm.com> wrote:
> >
> > > On 11/22/2018 11:54 AM, Cornelia Huck wrote:
> > >
> > > ...snip...
> > >
> > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > > index 813102810f53..565669f95534 100644
> > > > --- a/include/uapi/linux/vfio.h
> > > > +++ b/include/uapi/linux/vfio.h
> > > > @@ -297,6 +297,7 @@ struct vfio_region_info_cap_type {
> > > >
> > > > #define VFIO_REGION_TYPE_PCI_VENDOR_TYPE (1 << 31)
> > > > #define VFIO_REGION_TYPE_PCI_VENDOR_MASK (0xffff)
> > > > +#define VFIO_REGION_TYPE_CCW (1 << 30)
> > >
> > > Oof. So the existing VFIO_REGION_TYPE_PCI_VENDOR_TYPE gets OR'd with
> > > another value (e.g., 8086). But in 4.20, there was a
> > > VFIO_REGION_TYPE_GFX is added as simply "1" ... Which direction are
> > > these definitions being added from? I guess asked another way, is
> > > _TYPE_CCW going to be OR'd with anything else that necessitates its
> > > presence as an identifier with some Other Thing, or should this follow
> > > the TYPE_GFX enumeration? Perhaps the type field needs to be tidied up
> > > to help this sit more cleanly now? (Sorry!)
> >
> > The semantics of that type stuff are really a bit unclear to me :(
> >
> > I don't think we'll ever do any fancy mask handling for ccw. It is
> > probably enough to have any kind of uniqueness within the different
> > types, so maybe counting up would be indeed enough...
>
> Just to confirm, this is the intended usage, simply reserve a new type
> following the GFX region example. We can define VFIO_REGION_TYPE_CCW
> as 2 and then there's a whole address space of sub-types to fill in
> within that. I might have over-engineered PCI a bit with the address
> space split, but it seemed like a good idea at the time to pre-define a
> type address space for each vendor, such that they only need to define
> the sub-types and we can avoid namespace collisions. Unfortunately
> this implicit definition for each PCI vendor also contributes to the
> confusion here. Sorry. Thanks,
>
> Alex

Thanks for the explanation. I'm simply switching VFIO_REGION_TYPE_CCW
to 2 in the next version.