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

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Date:	Sat, 12 Jan 2008 20:42:48 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	tcamuso@...hat.com
Cc:	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 Sat, 12 Jan 2008 20:36:59 -0500
Tony Camuso <tcamuso@...hat.com> wrote:

> Thanks, Arjan.
> 
> The problem we have been experiencing has to do with Northbridges,
> not with devices.

correct for now.
HOWEVER, and this is the point Linus has made several times:
Just about NOBODY has devices that need the extended config space. At all.
So making this opt-in for devices allows our users to boot and use
their system if they are in the majority that has no need for even getting
close to this mess.

> 
> As far as the device is concerned, after the Northbridge translates
> the config access into PCI bus cycles, the device has no idea what
> mechanism drove the Northbridge to the translation.

Wanne bet there'll be devices that screw this up? THere's devices that even screwed
up the 64-256 region after all.

> The patch I devised concerned itself with Northbridges and separated
> MMCONFIG-compliant buses from those that could not handle MMCONFIG.

THis kind of patchup has been going on for the better part of a year (well 2 years)
by now and it's STILL NOT ENOUGH, as you can see by the more patchups that have
been proposed as "alternative" to my approach.

> 
> In my humble opinion, Port IO config access is here to stay, having
> been defined as an architected mechanism in the PCI 2.1 spec.
> 
> This is most especially true for x86.
> 
> In other words, for x86, I don't think we need to worry about Port
> IO config access ever going away at all.

You're wrong there. Sad to say, but you're wrong there.

-- 
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