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Subject: Re: [PATCH] windfarm: add PowerMac 12,1 support
From: David Woodhouse <dwmw2@infradead.org>
To: benh@kernel.crashing.org
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Date: Sat, 22 Mar 2008 23:02:46 +0000
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On Sun, 2008-03-23 at 09:13 +1100, Benjamin Herrenschmidt wrote:
> On Sat, 2008-03-22 at 19:35 +0000, David Woodhouse wrote:
> > On Sat, 2008-01-26 at 12:55 +0100, Étienne Bersac wrote:
> > > From: Étienne Bersac <bersace@gmail.com>
> > > 
> > > Implement a new driver named windfarm_pm121 which drive fans on PowerMac
> > > 12,1 machine : iMac G5 iSight (rev C) 17" and 20". It's based on
> > > windfarm_pm81 driver from Benjamin Herrenschmidt.
> > 
> > Is it just coincidence, or does it only seem to stop the fans when I
> > cat /sys/devices/platform/windfarm.0/cpu-temp ? 
> 
> Is it actually working ?
> 
> If the SMU thinks there is no fan control done by the OS, it will ramp
> them up ... but bring them back down when it gets ping.
> 
> So if for some reason the control loop isn't starting (because it can't
> find something it wants on this machine), the fans will stay up, but
> you'll cause such a "ping" when reading the CPU temp.

Yeah, there's weird shit going on with the sensor/control registration.
I think GCC is be miscompiling it -- the sequence of
	all = all && pm121_register_control(foo...);
	all = all && pm121_register_control(bar...);
is bailing out as soon as 'all' gets set to zero. Despite the fact that
pm121_register_control() quite blatantly has side-effects.

-- 
dwmw2