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

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Date:	Mon, 14 Jan 2008 08:01:50 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	tcamuso@...hat.com
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

On Mon, 14 Jan 2008 10:23:14 -0500
Tony Camuso <tcamuso@...hat.com> wrote:

> 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.

it's not pci_enable_mmconf(), it's pci_enable_extended_config_space... it's independent of the mechanism!

> 
> 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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