Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driveropt-in
From: Robert Hancock
Date: Sat Jan 12 2008 - 20:56:19 EST
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
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Home Page: http://www.roberthancock.com/
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