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

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Message-ID: <20090519203015.GA1362@ucw.cz>
Date:	Tue, 19 May 2009 22:30:15 +0200
From:	Pavel Machek <pavel@....cz>
To:	Peter Feuerer <peter@...e.net>
Cc:	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 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 

Well... hw is usually designed to protect itself.

>> That's not so optimal, I'd say. The kernel module should _replace_
>> the userspace program, not work alongside it, since the last is flaky
>> and unreliable, and this was the main reason the kernel module was
>> introduced in the first place - to control the fan from kernel space,
>> which is the more sane choice.
>
> The main reason to do this in kernel was the availabilty of atomic ec- 
> read and write functions. But I agree with you that either kernel or BIOS 
> should control the fan and not a userspace tool. I added the user mode 
> just because it wasn't really much more code than just an implementation 
> of the enable/disable functionality.

Kernels crash, too, just like userspace does. It would still make
sense to allow userspace to increase fan speed.
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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