Re: [Xen-devel] [PATCH v6 07/30] PCI: Pass PCI domain number combined with root bus number

[Manish Jaggi <mjaggi@xxxxxxxxxxxxxxxxxx>]

On Tuesday 17 March 2015 07:35 PM, Ian Campbell wrote:
> On Tue, 2015-03-17 at 10:45 +0530, Manish Jaggi wrote:
> > On Monday 09 March 2015 08:04 AM, Yijing Wang wrote:
> > > Now we could pass PCI domain combined with bus number
> > > in u32 argu. Because in arm/arm64, PCI domain number
> > > is assigned by pci_bus_assign_domain_nr(). So we leave
> > > pci_scan_root_bus() and pci_create_root_bus() in arm/arm64
> > > unchanged. A new function pci_host_assign_domain_nr()
> > > will be introduced for arm/arm64 to assign domain number
> > > in later patch.
> > Hi,
> > I think these changes might not be required. We have made very few
> > changes in the xen-pcifront to support PCI passthrough in arm64.
> > As per xen architecture for a domU only a single pci virtual bus is
> > created and all passthrough devices are attached to it.
> I guess you are only talking about the changes to xen-pcifront.c?
> Otherwise you are ignoring the dom0 case which is exposed to the real
> set of PCI root complexes and anyway I'm not sure how "not needed for
> Xen domU" translates into not required, since it is clearly required for
> other systems.
>
> Strictly speaking the Xen pciif protocol does support multiple buses,
> it's just that the tools, and perhaps kernels, have not yet felt any
> need to actually make use of that.
>
> There doesn't seem to be any harm in updating pcifront to follow this
> generic API change.
ok.

One side question, the function

 pci_host_assign_domain_nr()

which would be introduced in later patch, does it appear to be doing the 
same binding which we are trying to implement via a pci_host_bridge add 
hypercall.
> Ian.

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