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

Jeff Garzik
2007-12-23T05:10:10Z

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