Re: RFC: Changes for PCI

From: Tom Gall (
Date: Thu Jun 28 2001 - 22:14:51 EST

Richard Henderson wrote:

> On Wed, Jun 27, 2001 at 02:07:37PM -0500, Tom Gall wrote:
> > Consider also in drivers/pci/pci.c:
> >
> > The function pci_bus_exists checks based on bus numbers. This function is
> > of course used by pci_alloc_primary_bus, which is in turn used by
> > pci_scan_bus. As is today, this code can break me the second I'm
> > onto my second PCI system domain.
> You'll find that the existing ports that support multiple pci
> domains do not number the busses on the secondary domains from
> zero. If domain 0 has 3 busses, then domain 1's root bus will
> be bus number 3, and so on.

Yes I've looked at this in depth, and it does work well to compact things down
and conserve on the precious and limited bus numbers.

> This approach works quite well in practice, even on machines
> with large numbers of pci domains, since there tends to be no
> pci-pci busses on domains other than the one containing legacy
> i/o widgetry.

We have pci-pci bridges in every PCI system domain. Additionally we have cards
that have pci-pci bridges on them and certainly they can be plugged in anywhere
on the system.

Unfortunately the majority of our problem is centered on the fact that in the
end we have more than 256 buses. I look forward to this limit disappearing in



Tom Gall - PPC64 Maintainer      "Where's the ka-boom? There was
Linux Technology Center           supposed to be an earth
(w)         shattering ka-boom!"
(w) 507-253-4558                 -- Marvin Martian

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