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Re: RFC: PCI devices passthrough on Arm design proposal

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.




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