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

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Date:	Sun, 23 Dec 2007 00:09:49 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Linus Torvalds <torvalds@...ux-foundation.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

Linus Torvalds wrote:
> 
> On Sat, 22 Dec 2007, Jeff Garzik wrote:
>> But regardless of problems, enabling should be done globally, not per
>> device...
> 
> I'm ok with trying the "globally" idea, but it has to be "globally but 
> only if absolutely required".
> 
> And quite frankly, how do you tell whether it's absolutely required or 
> not?
> 
> I have an idea: the drivers that really need it will do a "please enable 
> MMCONFIG, because I will need it" thing?
> 
> Ok?
> 
> And then, since we *need* such a "pci_enable_mmconfig()" call anyway, why 
> not let the driver give which device it controls too, so that we can print 
> out the information (in case the machine then hangs immediately 
> afterwards), and perhaps - if it is shown to help - only do the MMCONFIG 
> cycles for that particular device?
> 
> Sounds like a plan?

As long as pci_enable_ext_cfg_space(pdev) enables extended accesses for 
-all- devices, the plan is mostly sound.

That largely eliminates the inconsistency issue.

The only thing I would worry about is whether "config space suddenly 
grew larger" condition will confuse userspace -- but that is NOT an 
objection, just a worry.

	Jeff



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