Reason for the "one dot" hang found!
corbet at lwn.net
Sat Jun 12 09:47:08 EDT 2010
[Sorry for the slow response...naturally enough I'm in Europe and
falling behind on things.
On Thu, 10 Jun 2010 18:01:34 -0400
Paul Fox <pgf at laptop.org> wrote:
> > I doubt it is directly related to locking.
> > If (as you say) there is no crash in the logs then I suspect it is
> > related to an infinite loop within the initialization code.
Definitely not locking, there is nothing complex or strange about the
> > And this all seems very familiar. Google for a thread titled
> > "cafe_ccic/ov7670 hang on boot" from the 8.2 days.
> > I suspect we never fixed that bug upstream and that same commit needs
> > to be reverted from the new kernel.
> good catch, good call. commit 8815ea29a9bcbab2a3c7fbc28987cac67c2c41d0
> is a revert for 6d77444aca298b43a88086be446f943cd0442ef7, and is present
> in the testing branch (i.e., XO-1 802 and earlier), but not in our
> current 2.6.31 branch.
Wow, ancient history. I don't really remember what I was thinking at
the time. Clearly we're seeing yet another i2c flake, something that
both Cafe and ov7670 are good at doing.
There are a couple of ways in which a rewrite of the i2c controller
code could help. Bypassing the Cafe SMBUS controller and letting the
kernel bit-bang the protocol would probably work a lot better than what
we have now. I can put that on my list, but I can't promise to get to
get to it soon - more travel looms.
- Just mainline the revert so you don't get burned again. I don't
believe there are any other users of the cafe_ccic driver, so
nobody's going to complain.
- Experiment with the timeout in the do...while loop; s/1/2/ might be
enough to keep from reading the TSIC1 register before it's prepared
to deal with the world again.
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