Re: RFC: PCI devices passthrough on Arm design proposal

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 20 Jul 2020, Rob Herring wrote:
> On Mon, Jul 20, 2020 at 5:24 PM Stefano Stabellini
> <sstabellini@xxxxxxxxxx> wrote:
> >
> > + Rob Herring
> >
> > On Fri, 17 Jul 2020, Bertrand Marquis wrote:
> > > >> Regarding the DT entry, this is not coming from us and this is already
> > > >> defined this way in existing DTBs, we just reuse the existing entry.
> > > >
> > > > Is it possible to standardize the property and drop the linux prefix?
> > >
> > > Honestly i do not know. This was there in the DT examples we checked so
> > > we planned to use that. But it might be possible to standardize this.
> >
> > We could certainly start a discussion about it. It looks like
> > linux,pci-domain is used beyond purely the Linux kernel. I think that it
> > is worth getting Rob's advice on this.
> >
> >
> > Rob, for context we are trying to get Linux and Xen to agree on a
> > numbering scheme to identify PCI host bridges correctly. We already have
> > an existing hypercall from the old x86 days that passes a segment number
> > to Xen as a parameter, see drivers/xen/pci.c:xen_add_device.
> > (xen_add_device assumes that a Linux domain and a PCI segment are the
> > same thing which I understand is not the case.)
> >
> >
> > There is an existing device tree property called "linux,pci-domain"
> > which would solve the problem (ignoring the difference in the definition
> > of domain and segment) but it is clearly marked as a Linux-specific
> > property. Is there anything more "standard" that we can use?
> >
> > I can find PCI domains being mentioned a few times in the Device Tree
> > PCI specification but can't find any associated IDs, and I couldn't find
> > segments at all.
> >
> > What's your take on this? In general, what's your suggestion on getting
> > Xen and Linux (and other OSes which could be used as dom0 one day like
> > Zephyr) to agree on a simple numbering scheme to identify PCI host
> > bridges?
> >
> > Should we just use "linux,pci-domain" as-is because it is already the de
> > facto standard? It looks like the property appears in both QEMU and
> > UBoot already.
> 
> Sounds good to me. We could drop the 'linux' part, but based on other
> places that has happened it just means we end up supporting both
> strings forever.

OK, thank you!