linux-kernel - Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in

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Date:	Sun, 13 Jan 2008 00:49:11 +0300
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Greg KH <greg@...ah.com>, Matthew Wilcox <matthew@....cx>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Mares <mj@....cz>, Tony Camuso <tcamuso@...hat.com>,
	Loic Prylli <loic@...i.com>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
	opt-in

On Sat, Jan 12, 2008 at 09:45:57AM -0800, Arjan van de Ven wrote:
> btw this is my main objection to your patch; it intertwines the conf1
> and mmconfig code even more.

There is nothing wrong with it; please realize that mmconf and conf1 are
just different cpu-side interfaces. Both produce precisely the *same* bus
cycles as far as the lower 256-byte space is concerned.

> When (and I'm saying "when" not "if") systems arrive that only have
> MMCONFIG for some of the devices, we'll have to detangle this again,
> and I'm really not looking forward to that.

MMCONFIG for *some* of the devices? This doesn't sound realistic
from technical point of view.
MMCONFIG-only systems? Sure. I really hope to see these. But it won't
be PC-AT architecture anymore. It has to be something like alpha,
for instance, fully utilizing the 64-bit address space, and we'll have
to have the whole low-level PCI infrastructure completely different
for these future platforms anyway.
Right now, each and every x86 chipset *does* require working
conf1 just in order to set up the mmconf aperture. It's the very
fundamental thing, sort of design philosophy.

Ivan.
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