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

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Date:	Tue, 29 Jan 2008 10:15:45 -0500
From:	Tony Camuso <tcamuso@...hat.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Greg KH <greg@...ah.com>, Matthew Wilcox <matthew@....cx>,
	Grant Grundler <grundler@...isc-linux.org>,
	Loic Prylli <loic@...i.com>, Adrian Bunk <bunk@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Jeff Garzik <jeff@...zik.org>,
	linux-pci@...ey.karlin.mff.cuni.cz, Martin Mares <mj@....cz>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
 opt-in

Arjan van de Ven wrote:
> On Tue, 29 Jan 2008 09:15:02 -0500
> Tony Camuso <tcamuso@...hat.com> wrote:
> 
>> Greg,
>>
>> The problem with Arjan's patch, if I understand it correctly, is that
>> it requires drivers to make a call to access extended PCI config
>> space.
>>
>> And, IIRC, Arjan's patch encumbers drivers for all arch's, even those
>> that have no MMCONFIG problems.
>>
>> The patches proposed by Loic, Ivan, Matthew, and myself, all address
>> the problem in an x86-specific manner that is transparent to the
>> drivers.
> 
> this is not quite correct; the patches from Loic, Ivan, Matthew and you are for a different
> problem statement.
> 
> Your patch problem statement is "need to fix mmconfig", my patch problem statement is "need
> to not make users who don't need it suffer". These are orthogonal problems.
> 
> 

Yes, but your patch also makes users who need extended PCI config space suffer.

Right now, that isn't a lot of people in x86 land, but your patch encumbers drivers
for non-x86 archs with an additional call to access space that they've never had
a problem with.

As more PCI express drivers start to take advantage of AER and other advanced
express capabilities, the extra call to address a condition specific to legacy
x86 hardware is, IMNSHO, a kludge.

The patches submitted by the others fix the problems with MMCONFIG without
encumbering the drivers to be aware of any difference between legacy config
space and extended config space.

I have tested these patches on a number of systems exhibiting various MMCONFIG-
related pathologies, and they work.




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