[ltp] WARNING for everyone doing ThinkPad fan control

[Daniel Castro]

Well I have Fan Control installed and I just use it on the "Quiet" mode. 
I suppose I'm on the safe side right?

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Daniel Castro
Networking and Distributed Systems
Computer Science
Trinity College Dublin

Mobile: 083-318-2058
86.4.3 Trinity Hall, Dartry Road, Dublin 6
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Henrique de Moraes Holschuh wrote:
> I have just added this warning to ThinkWiki's fan control page:
>
> === WARNING: ================================================
> When designing fan-control applets, never ignore a valid thermal sensor.
>
> Even if it seems to be stuck at a certain temperature, you must take that
> sensor into account.  While it will probably make the fan spin faster than
> if the sensor was ignored, that's exactly what would happen when the fan is
> under EC control, and could very well be the reason for the "stuck" value in
> the first place.
>
> Always play it safe.  If a battery pack seems to want the fan to always run
> faster, the only safe thing to do is to make it run faster.
> =============================================================
>
> The facts as I know them:
>
> 1.  As far as I could find out, there are no battery packs with defective
> thermal sensors in the field:  Lenovo would have exchanged those right away
> if they were defective, and the Windows utility doesn't flag them as
> defective, either.  I got some information that implies the Windows utility
> is correct (the packs are not defective).
>
> 2.  Some battery packs have been observed to have a sensor "stuck" at 50C.
> It is plain impossible for a Linux bug to get *just* that reading incorrect.
>
> 3.  The EC won't turn the fan off (and in fact, probably not let it go below
> level 3) if a sensor is at 50C.
>
> 4.  The Windows utility is not showing the temperature as 50C (there are two
> sensors per pack, one near the cells, the other in the charger/monitor), so
> it looks like that sensor is not the more important thermal sensor of the
> battery pack.
>
> Do the math.
>
> Don't use fan control to run the machine any hotter than the EC would.
> There is a damn good reason why the drivers require EXPLICIT configuration
> by the user to even ENABLE fan control.
>
> You have been warned.   
>
>