Re: [RFC PATCH v1 1/4] arm/pci: PCI setup and PCI host bridge discovery within XEN on ARM.

[Julien Grall <julien@xen.org>]

On 24/07/2020 18:41, Stefano Stabellini wrote:
> On Fri, 24 Jul 2020, Julien Grall wrote:
>> On 24/07/2020 00:38, Stefano Stabellini wrote:
>> The segment number is just a value defined by the software. So as long as
>> Linux and Xen agrees with the number, then we should be ok.
> 
> As far as I understand a Linux "domain" (linux,pci-domain in device
> tree) is a value defined by the software. The PCI segment has a
> definition in the PCI spec and it is returned by _SEG on ACPI systems.
> 
> The link above suggests that a Linux domain corresponds to (_SEG,
> _BBN) where _SEG is the segment and _BBN is the "Bus Number".
>
> I just would like to be precise with the terminology: if we are talking
> about domains in the linux sense of the word, as it looks like we are
> doing, then let's call them domain instead of segments which seem to
> have a different definition.

You seem to argue on the name but this doesn't resolve the underlying 
problem. Indeed, all our external interfaces are expecting a segment number.

If they are not equal, then I fail to see why it would be useful to have 
this value in Xen. In which case, we need to use 
PHYSDEVOP_pci_mmcfg_reserved so Dom0 and Xen can synchronize on the 
segment number.

Cheers,

-- 
Julien Grall