Re: [PATCH] Acer Aspire One Fan Control

Hi,

On Mon, May 11, 2009 at 08:05:07PM +0200, Peter Feuerer wrote:
Hello,

Borislav Petkov writes:

the more I'm looking at the driver, the more I get annoyed by that
user/kernel mode operation split. Remind me again why the driver should
be loaded and not started automatically but the user should be required
to activate it explicitly?

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
invalid when you do that. Not sure about how acer would handle a defect
which could be caused by overheating and when they detect that software
was controlling the fan. That's why I think Matthew is right.

We actually don't have any reliable source for the temperature envelope
of the surrounding hardware, right? Quick search didn't reveal anything
here. I only came across a bunch of freeware tools which do fan control
of the aspire ones but all the temperature trip points for the fan in
those were ranging from 50 - 63° which leads to think that those all are
kinda "common sense"-settings the authors came up with without any hard
data from the manufacturer.

For example, mine has a Seagate Momentum ATA-8 ST9160310AS hdd and its
spec[¹] says:

"2.10.1 Ambient temperature

Ambient temperature is defined as the temperature of the environment
immediately surrounding the drive. Actual drive case temperature should
not exceed 65°C (149°F) within the operating ambient conditions."

From what I could measure here empirically, the fan starts in low RPM
mode at around 37°C and and gets cranked up to max when the temp
reaches ~55°C. This envelope in the BIOS code is taking surrounding
devices into consideration, I guess and am wondering whether the 67°C
setting in your driver is still within safe limits, hmmm?

[..]

What is more, if the userspace program would fail, there's no way
for the module to get activated again and jump in instead of the
userspace program to the rescue. Which goes more to show that you
don't need userspace control _at_ _all_ and the only two agents
controlling the fan should be the BIOS or the kernel module.

After reading and thinking about all this a while, I agree with you.
In the next patch I won't allow the user to switch on/off the fan
anymore.

Cool.

So I think that the kernel module should take over fan control
upon load. This way you'll be able to get rid of all that needless
complexity around kernelmode/disable_kernelmode and have a simple
clean design.

I would really like to do that, but what do you think about the
hardware damage / warranty things written above?

It seems that the BIOS setting is lower/safer so, yes, you're right, we
don't want to void any warranties, so the BIOS control _should_ actually
be the default since we are not at all sure whether moving the envelope
up the temperature scale won't hurt the hardware.

/me would love to see some reliable info on that from the manufacturer...

[..]

Thanks for your work.


¹http://www.seagate.com/staticfiles/support/disc/manuals/notebook/momentus/5400.4/SATA/100468842a.pdf

--
Regards/Gruss,
Boris.
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