linux-kernel - Re: [PATCH] Acer Aspire One Fan Control

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Date:	Fri, 22 May 2009 16:09:30 +0200
From:	Pavel Machek <pavel@....cz>
To:	Borislav Petkov <petkovbb@...glemail.com>
Cc:	Peter Feuerer <peter@...e.net>, petkovbb@...il.com,
	LKML <linux-kernel@...r.kernel.org>, lenb@...nel.org,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Maxim Levitsky <maximlevitsky@...il.com>
Subject: Re: [PATCH] Acer Aspire One Fan Control

Hi!

> >> The idea of not starting the module in kernel mode was from Matthew. And
> >> he stated that it could harm the hardware when software controls the fan
> >> instead of the BIOS. It may also be possible, that the warranty gets
> >
> > Well... hw is usually designed to protect itself.
> 
> It seems like the fan in the aspire one's is used for cooling the
> surrounding devices too and while the thermal envelope of the CPU is
> much wider, the peripherals are much more susceptible to temperatures
> outside of their allowed operating range. That's why currently the
> driver lets the BIOS control the fan since its settings are most
> conservative.

Yep, I don't disagree. But I strongly suspect that if you force the
fan off and overheat the machine, it will shut down in hardware before
doing any damage.

> > Kernels crash, too, just like userspace does. It would still make
> > sense to allow userspace to increase fan speed.
> 
> Well, if the kernel is dead, userspace has already died
> too. 

Yep.

> the module can still be toggled on/off from sysfs. Actually, empirically
> measured, there seem to be three states of the fan: off, on and on-max
> where you can hear it rotating at max RPM. The kernel module can handle
> those completely if you know the respective ACPI EC commands and there's
> no need for userspace daemon, IMHO.

It would be still nice to let the userspace lower the trip points for
maximum flexibility. No need for userspace _daemon_.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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