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

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.


Julien Grall



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