linux-kernel - Re: Dell Latitude E6440 & i8k

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Message-ID: <20140517230940.25c36f07@endymion.delvare>
Date:	Sat, 17 May 2014 23:09:40 +0200
From:	Jean Delvare <jdelvare@...e.de>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Pali Rohár <pali.rohar@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Dell Latitude E6440 & i8k

On Sat, 17 May 2014 08:25:38 -0700, Guenter Roeck wrote:
> On 05/16/2014 12:11 PM, Jean Delvare wrote:
> > Load the i8k driver with fan_mult=1.
> 
> Would it make sense to change the default multiplier to 1 ?
> Lots of people have problems with it, and trying to figure out
> affected machines one by one would be an all but impossible task.

That would cause a regression on many (presumably older) machines. I
doubt this is acceptable. One option would be to use the ACPI year to
change the default, if indeed all new machines need fan_mult=1. I don't
know if this is the case.

One this I had in mind was auto-detecting the scaling factor. AFAIK
only 30 and 1 are possible values, so any value above ~300 would imply
scaling factor of 1 (30 would make it > 9000 RPM which is unrealistic.)
But I don't know if we can actually do that, as such a simple heuristic
could easily fail is the fan is stopped (30 * 0 == 1 * 0) or if the
returned raw speed is temporarily unreliable for whatever reason.

I have to admit that working on a reverse engineered driver for
hardware I don't even have isn't quite at the top of my to-do list.

-- 
Jean Delvare
SUSE L3 Support
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