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

Robert Hancock
2008-01-13T01:56:18Z

Linus Torvalds wrote:
>
> On Fri, 11 Jan 2008, Matthew Wilcox wrote:
>> Did I miss a bug report? The only problems I'm currently aware of are
>> the ones where using MMCONFIG during BAR probing causes a hard lockup on
>> some Intel machines, and the ones where we get bad config data on some
>> AMD machines due to the configuration retry status being mishandled.
>
> Hmm. Were all those reports root-caused to just that BAR probing? If so,
> we may be in better shape than I worried.

As far as I'm aware, the known MMCONFIG-related issues that I'm aware of
are or have been:

-Some devices built into the AMD K8 integrated northbridge can't be
reached by MMCONFIG - already handled

-Overlap of device BAR and MMCONFIG aperature during BAR sizing causing
lockup - can be avoided by disabling device decode during BAR sizing.

-PCI Express CRS-related issues - already handled by disabling CRS by
default

-Devices behind certain host bridges (some AMD HT to PCI-X bridges,
others?) can't be reached by MMCONFIG - can be handled by Tony Camuso's
patch or something similar (note that this is really a BIOS bug, it
should not list those buses in the MCFG table if MMCONFIG cannot access
them, and if it didn't I think we could already handle that)

-Some issue with some AMD CPUs needing MMCONFIG accesses to use a
certain register I believe? already handled?

Of these, I think the PCI BAR/MMCONFIG overlap problem is responsible
for by far the most cases of machines thought to have "broken MMCONFIG",
when in fact they were nothing of the sort. I don't recall hearing of a
single machine where MMCONFIG really just didn't work at all.

As I've mentioned before, all of these issues (well, I suppose not the
BAR overlap one) need to be resolved whether we have Arjan's patch or
not, otherwise if a driver does opt in and tries to use extended config
space it will still break. And if they are resolved, the patch seems
quite pointless.

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/