Re: [patch] pci: revert "PCI: remove transparent bridge sizing"

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2008-03-26 at 23:10 +0100, Ingo Molnar wrote:
> > PCI bridges at zero is perfectly valid indeed and I'm sure we have 
> > that around at least for IO space. In fact, I'm surprised you don't 
> > have that on x86. Typically, things like an HT segment with a P2P 
> > bridge and behind that bridge an ISA bridge could well have the P2P 
> > bridge with a resource forwarding 0...0x1000 IO downstream for example 
> > even on x86 no ? (I'm not -that- familiar with the crazyness of legacy 
> > ISA on x86 but I've definitely seen such setup on other archs).
> 
> 0..0x1000 physical memory (== bus memory on x86) is reserved to the BIOS 
> as RAM in essence and that legacy will be with us for at least 100 or 
> maybe 200 years ;-)

I was talking about IO not memory mostly here. MMIO wouldn't be a
problem on powerpc as I said because we offset MMIO resources early
after probe so that they contain effectively a CPU bus address, and in
that case, 0 is definitely not going to happen for PCI devices or busses
(even if it may on the bus, but the code we are talking about won't see
it).

Cheers,
Ben.