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Subject: Re: i2c-powermac fails
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Jean Delvare <khali@linux-fr.org>
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Date: Fri, 16 Oct 2009 19:42:36 +1100
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Cc: Paul Mackerras <paulus@samba.org>, Tim Shepard <shep@alum.mit.edu>,
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On Fri, 2009-10-16 at 09:44 +0200, Jean Delvare wrote:
> On Thu, 15 Oct 2009 16:05:13 +0200, Jean Delvare wrote:
> > On Thu, 15 Oct 2009 22:19:19 +1100, Benjamin Herrenschmidt wrote:
> > > On Thu, 2009-10-15 at 12:49 +0200, Jean Delvare wrote:
> > > > Oh. Well, if that was the case, we would see errors all the time, not
> > > > just during initialization, right? Or does the I2C clock frequency
> > > > change over time somehow?
> > > 
> > > No but maybe we are a bit on the "limit" of the device and some
> > > registers take long to respond than others ?
> > 
> > Unlikely. The ADT7460 can run at I2C clock rates up to 400 kHz while
> > the Keywest I2C runs at 25, 50 or 100 kHz if I read the code properly.
> > I don't know what exact speed is used on Tim's system, apparently it is
> > read from the hardware in the device tree directly?
> > 
> > We could have low_i2c.c log the I2C clock frequency and/or try to force
> > the lowest speed (25 kHz) and see if it helps, but I very much doubt
> > it. And I'd rather wait for Tim to report the result with my last patch
> > first.
> 
> Ben, wouldn't this recent patch of yours be worth testing too?
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=11a50873ef2b3c1c3fe99a661c22c08f35d93553
> 
> If it solves problems at resume time, I guess it might also solve
> problems at boot time?

I doubt it. The problem was related to the way interrupts get turned off
at suspend time by the generic code, which is unrelated to what happens
at boot.

Cheers,
Ben.