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

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Message-ID: <alpine.LFD.0.9999.0712222036010.21557@woody.linux-foundation.org>
Date:	Sat, 22 Dec 2007 20:40:14 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jeff Garzik <jeff@...zik.org>
cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, gregkh@...e.de,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [patch] Make MMCONFIG space (extended PCI config space) a driver
 opt-in issue

On Sat, 22 Dec 2007, Jeff Garzik wrote:
> 
> It should be self-evident that mmconfig doesn't work on old hardware, is not
> needed on old hardware, should not be turned on for old hardware, and in
> general should never disturb old hardware.

.. but it does. How do you figure out when to turn it off?

By "old hardware" I don't mean stuff from the last century, that generally 
doesn't even *have* MMCONFIG. I mean the stuff you can buy *today*, which 
will be old by the time people really start _needing_ MMCONFIG.

The fact is, 99% of the hardware you buy *today* has absolutely zero need 
for extended PCI config access. In fact, I would not be surprised at all 
if most hardware sold today generally doesn't have *any* devices that even 
have config registers in the 0x100+ range.

So those are the kinds of machines we want to protect from blowing up. 
Stuff that isn't sold with Vista, and has never been tested (or where 
vista does some work-arounds we don't even know about - somebody was 
mentioning things like looking at the BIOS date etc).

			Linus
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