On Friday 22 June 2012, Bjorn Helgaas wrote:

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.

The part that is specific to PCs is that they don't have PCI domains
normally.

	Arnd