Re: [Qemu-devel] [0/2] pseries: Rework PCI code for handling multiple PHBs

[Michael S. Tsirkin]

On Tue, Nov 27, 2012 at 05:07:31PM +1100, David Gibson wrote:
> Hi Michael, Alex,
> 
> This patch represents a compromise I hope will be acceptable after the
> long thread discussing handling of multiple PCI host bridges on the
> pseries machine.  Patch 1/1 is just a preliminary enforcing uniqueness
> of LIOBNs in the IOMMU code.
> 
> Patch 2/2 is the meat.  It allows either explicit configuration of all
> the properties, or the user can just set an abstract index which will
> generate sensible and probably-unique values for all the rest.
> 
> With these patches I was able to do something like:
>       qemu-system-ppc64 -M pseries -m 1024 -nographic \
>       fc17-root.qcow2 -net none -device nec-usb-xhci -device \
>       spapr-pci-host-bridge,index=1 -device e1000,netdev=fred \
>       -netdev user,id=fred
> 
> I was able to see both the PCI domains in the guest, and use the NIC
> on the secondary domain.
> 
> There are still some gotches with multiple domains though.  The domain
> value in PCIHostBus is still always initialized to 0, and there are
> other places in the PCI core where handling of multiple domains is
> essentially stubbed out.
> 
> Michael, any thoughts on what to do about that?  I could fix up the
> PCI code so that domain is actually set and used.  But I think the
> whole notion of domain numbers is kind of bogus on the qemu side:
> since PCI domains are completely independent from each other, it's
> only platform convention which determines what the domain numbers are.
> On platforms that don't have a strong convention, the guest will
> number them itself and we have no way of knowing that.  So it seems to
> me that the PCI code should instead of domain numbers just use the
> device ID, or the bus name or some qemu side symbolic name.  For
> platforms that do have a numbering convention those names can be
> derived from the domain numbers, but it also works for platforms that
> don't.

I agree with this last statement: using bus numbers and domain
numbers is not a good idea. We mostly need to support domain 0
to mean "default" for backwards compatibility.
I'll review the patchset shortly.

-- 
MST