linux-kernel - [VIA Support] Instruction timing and cache coherency issues

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Message-Id: <200907250827.43400.lkml@morethan.org>
Date:	Sat, 25 Jul 2009 08:27:39 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	linux-kernel@...r.kernel.org
Cc:	Harald Welte <HaraldWelte@...tech.com>
Subject: [VIA Support]  Instruction timing and cache coherency issues

Started back in mid-May - long time and a lot of hours later...

As suggested very early in this examination by others -
It is a timing issue.  My inserting "lock" for config_mviac7
was just poking at the edges of the sore spot.  ;)

The "break through" came yesterday while running (or trying to run)
FreeBSD-8.0-beta2 on the various machines at hand. . .

Depending on the cpu model variation and the integrated chipset
used with that cpu - -
*) FB-8.0 will run
*) FB-8.0 will only run in "safe mode"
*) FB-8.0 panics

And that pattern is similar to the 2.6.30 cpu model / chipset pattern.
Scratches head, asking: "now how can that be" with two very different OS designs.

Diddling with the things I have found that either "fix" or "work around"
the various timing / cache coherency issues - - -
Aw, so - found how to affect the timing issues sufficiently so that Linux
would panic dump rather than deadlock on the troublesum combination - -
*Functionally the same* panic backtrace that FreeBSD is showing.

NOW I have a lead into making a "minimum invasive" change so that the 
kernel is happy - even on the flaky VIA combinations.  Patch RSN, just any month.
The FreeBSD project can fix their problems themselves.  ;)

@H.W.  Download the FreeBSD-8.0-beta2 and try running it on your Cloudbook and HP-2133,
you can see what is happening.  Then you might have a word or two with the silicon growers.

Mike
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