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

Jeff Garzik
2007-12-23T05:04:53Z

Linus Torvalds wrote:
> I want to limit that downside. Right now, the easiest way to limit it
> seems to be to say that those (very very few) drivers that actually care
> could enable it. That way, we automatically limit it to only those
> machines that have hardware that cares.

Then let's do it right: disable mmconfig by default on x86, and enable
it when passed "pci=mmconfig".

For the rare -- you and I agree its very rare -- case where it is
REQUIRED, the user can pass pci=mmconfig as instructed by driver
documentation somewhere.

Let's not bend over backwards and introduce an API for these
presently-theoretical cases. Given the complete lack of hw vendor
testing and potential to confuse userspace, the two choices for a
computer should be "mmconfig off" or "mmconfig on."

Kernel hackers developing drivers and code for new machines will know
enough to pass pci=mmconfig if they NEED it. That practice will only
become annoying when x86 hardware actually starts to NEED extended
config space -- at which future time we can revisit, as you describe.

> And yes, if you want the capability following to notice automatically when
> capabilities really do go into the 0x100+ range, that's fine. I suspect

Yes, we /must/ do this checking, if we don't already.

Jeff