Re: Xen/arm: Virtual ITS command queue handling

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-05-19 at 19:34 +0530, Vijay Kilari wrote:
> On Tue, May 19, 2015 at 7:24 PM, Ian Campbell <ian.campbell@citrix.com> wrote:
> > On Tue, 2015-05-19 at 14:36 +0100, Ian Campbell wrote:
> >> On Tue, 2015-05-19 at 14:27 +0100, Julien Grall wrote:
> >> > With the multiple vITS we would have to retrieve the number of vITS.
> >> > Maybe by extending the xen_arch_domainconfig?
> >>
> >> I'm sure we can find a way.
> >>
> >> The important question is whether we want to go for a N:N vits:pits
> >> mapping or 1:N.
> >>
> >> So far I think we are leaning (slightly?) towards the 1:N model, if we
> >> can come up with a satisfactory answer for what to do with global
> >> commands.
> >
> > Actually, Julien just mentioned NUMA which I think is a strong argument
> > for the N:N model.
> >
> > We need to make a choice here one way or another, since it has knock on
> > effects on other parts, e.g the handling of SYNC and INVALL etc.
> >
> > Given that N:N seems likely to be simpler from the Xen side and in any
> > case doesn't preclude us moving to a 1:N model (or even a 2:N model etc)
> > in the future how about we start with that?
> >
> > If there is agreement in taking this direction then I will adjust the
> > relevant sections of the document to reflect this.
> 
> Yes, this make Xen side simple. Most important point to discuss is
> 
> 1) How Xen maps vITS to pITS. its0 -> vits0?

The choices are basically either Xen chooses and the tools get told (or
"Just Know" the result), or the tools choose and setup the mapping in
Xen via hypercalls.

> 2) When PCI device is assigned to DomU, how does domU choose
>     vITS to send commands.  AFAIK, the BDF of assigned device
>     is different from actual BDF in DomU.

AIUI this is described in the firmware tables.

e.g. in DT via the msi-parent phandle on the PCI root complex or
individual device.

Is there an assumption here that a single PCI root bridge is associated
with a single ITS block? Or can different devices on a PCI bus use
different ITS blocks?

Ian.