linux-kernel - Re: radeonfb i2c regression post-2.6.18.

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Date:	Sat, 24 Nov 2007 12:11:04 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Michael Buesch <mb@...sch.de>,
	Roger Leigh <rleigh@...nlatter.ukfsn.org>,
	linux-kernel@...r.kernel.org, Dennis Munsie <dmunsie@...ropia.com>
Subject: Re: radeonfb i2c regression post-2.6.18.

On Fri, 2007-11-23 at 23:29 +0100, Jean Delvare wrote:
> On Fri, 23 Nov 2007 17:00:52 +0100, Michael Buesch wrote:
> > This patch fixes my crash problem.
> 
> Out of curiosity, what kind of crash was it? I admit that I can't see
> how the code could crash.

Really sneaky... apparently, keeping the i2c lines asserted on his
laptop model would drain enough current through the pullups (or the
chip) that the temperature will raise significantly, causing a thermal
shutdown if the machine was already warm.

A bit scary... looks to me that a pullup is a bit too weak somewhere on
the motherboard.

That also means that this fix should reduce power consumption on the
battery significantly on those machines as it must take quite a bit of
power to increase the temperature that significantly (either that, or
the heating part sits just next to the sensor).

Cheers,
Ben. 

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