On Friday 22 June 2012, Bjorn Helgaas wrote:

On Fri, Jun 22, 2012 at 10:53 AM, Arnd Bergmann [off-list ref] wrote:

quoted

On Friday 22 June 2012, Bjorn Helgaas wrote:

quoted

The requirement (if there is one) isn't anything related to PC-ness.
I just don't understand how things can actually work if two host
bridges both claim the same bus number.  If we do a config read to
that bus, both bridges should claim it and turn it into config cycles
on their respective root buses, and we should get two responses.  I
would expect the second response to cause an "unexpected response"
machine check or similar.

But each PCI domain has its own config space, so if you do a config
read for one bus, it's always relative to the domain.

Oh, I see!  I totally missed the fact that each host bridge was in its
own domain.  If each has its own domain, then the bus number aperture
can certainly be [bus 00-ff] and there's no problem.

Right. On my side, it took me a while to figure out that you can
actually have multiple root ports in one domain ;-)

	Arnd