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

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Message-ID: <9ea470500905220753x6c2be25dq14422dff2acea422@mail.gmail.com>
Date:	Fri, 22 May 2009 16:53:59 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Pavel Machek <pavel@....cz>
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

>> >> 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.

Yep, however we won't come that far with the current driver since it
relinquishes control of the fan to the BIOS after a critical temp of
89° is reached. I'm still quite unpersuaded about that "magical" number
since it is 1 degree below the high interval boundary of the juncture
temperature of the Atom CPU. I would like to have a more reliable source
for the allowed envelope based not only on the CPU but on the whole
chipset but can't seem to find any data from Acer on that.

>> 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_.

I'm sure Peter wouldn't mind adding some other sysfs entries in future
versions of the driver controlling exactly that.

-- 
Regards/Gruss,
Boris.
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