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

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Message-Id: <1206572084.6926.34.camel@pasglop>
Date:	Thu, 27 Mar 2008 09:54:44 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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 15:47 -0700, Linus Torvalds wrote:
> > I was talking about IO not memory mostly here.
> 
> Yeah, low IO is also reserved on PC's (the low 256 IO ports are 
> motherboard resources and contain stuff like legacy DMA channel setup 
> etc)

Sure but can't that be in a kind of southbridge ? Like HT or PCIe
segment out of the CPU gets through a virtual P2P wich then hits the
"legacy" combo blob masquerading as a PCI device ? I remember seeing
that sort of thing in the past and I -think- it was some kind of x86
chipset hijacked on powerpc... 

> You could imagine having it behind a PCI bridge, but in practice it's 
> always on the NB/SB (and if you want to support some of the odder
> things 
> like the NMI reason and the i387 error ports, they pretty much have
> to 
> be - it would be insane to make a special PCI chips on a separate bus 
> that does things like that).

It's often all virtual inside a single chip.

Anyway, doesn't matter much at this stage I suppose, but it would be
nice to not use 0 as meaning invalid when sizing bridge windows and I'm
not sure at all about using "start" as an alignment indicator neither...
It will be much over-aligned in some cases, adding constraints to the
allocator where we didn't have any before no ?

Ben.

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