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

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Message-Id: <1206570546.6926.30.camel@pasglop>
Date:	Thu, 27 Mar 2008 09:29:06 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Gary Hade <garyhade@...ibm.com>,
	Thomas Meyer <thomas@...3r.de>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Natalie Protasevich <protasnb@...il.com>, pm@...ian.org
Subject: Re: [patch] pci: revert "PCI: remove transparent bridge sizing"


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.
 

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