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

[Michael S. Tsirkin]

On Wed, Nov 28, 2012 at 01:50:53PM +1100, David Gibson wrote:
> On Tue, Nov 27, 2012 at 02:36:57PM +0200, Michael S. Tsirkin wrote:
> > 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.
> 
> Ok.  Where are domain numbers actually specified by the qemu user?

pci_parse_devaddr

> -- 
> David Gibson                  | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au        | minimalist, thank you.  NOT _the_ 
> _other_
>                               | _way_ _around_!
> http://www.ozlabs.org/~dgibson