Re: [qemu-s390x] [PATCH 1/3] vfio-ccw: add capabilities chain

[Eric Farman]

On 12/18/2018 12:24 PM, Cornelia Huck wrote:
> On Mon, 17 Dec 2018 16:53:34 -0500
> Eric Farman <address@hidden> 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 :(

+1

I was confused when I first looked at this.  When I applied it to 4.20, 
I got another level of confusion.  ;)

> 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...

Considering the subtype space, I think it would be fine too.  But wanted 
to ask in case I've been out of the loop on something.

> >    - Eric
> >
> > >    
> > >    /* 8086 Vendor sub-types */
> > >    #define VFIO_REGION_SUBTYPE_INTEL_IGD_OPREGION       (1)
> > >