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

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Date:	Mon, 14 Jan 2008 10:23:14 -0500
From:	Tony Camuso <tcamuso@...hat.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	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>, Loic Prylli <loic@...i.com>,
	Prarit Bhargava <prarit@...hat.com>,
	"Chumbalkar, Nagananda" <Nagananda.Chumbalkar@...com>,
	"Schoeller, Patrick (Linux - Houston, TX)" <Patrick.Schoeller@...com>,
	Bhavana Nagendra <bnagendr@...hat.com>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
 opt-in

Arjan van de Ven wrote:
> On Mon, 14 Jan 2008 08:01:01 -0500
> Tony Camuso <tcamuso@...hat.com> wrote:
 >>
>> If we're going to differentiate MMCONFIG from
>> some other access mechanism, it only needs to be done at the
>> Northbridge level. Devices are electrically ignorant of the protocol
>> used between CPU and Northbridge to get the Northbridge to assert
>> config cycles on the bus.
> 
> Again this is about having systems that don't need extended config space not use it. At all.
> The only way to do that is have the drivers say they need it, and not use it otherwise.
> It has NOTHING to do with how things are wired up. It's pure a kernel level policy decision
> about whether to use extended config space AT ALL.
> 

The problem with compelling device drivers to determine the PCI
config mechanism is that it must be forced upon arches that
have no PCI configuration quirks or don't even use the same
PCI config mechanisms as x86.

I don't think that's a good policy.

Better to confine arch-specific quirks to the arch-specific code
whenever possible.

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