Re: [ACPI-sppt] fan speed control techniques (again)

From: "Emma Jane Hogbin" <[email protected]>

> http://www.analog.com/library/analogDialogue/archives/34-04/fan/
> I thought this was an interesting article. I'm not sure how much of it has
> been implemented in the Linux stuff, but it was pretty easy to read. (Yes,
> it's old.) I noticed that it said my fan shouldn't be turned on until 60C,
> but the fan is currently on at:

I haven't read it thoroughly yet, but I don't believe it said that.  It's
showing a specific implementation which turns on the fan at 60.  It also shows
one that turns on the fan at 50.  When the fan should turn on is determined by
each manufacturer based on numerous conditions.  The specific capabilities of
the CPU probably being the most important.

> I noticed in a patch changelog that I found that:
> <[email protected]>
>    ACPI: Fix thermal management and make trip points R/W (Pavel Machek
> http://www.linuxhq.com/kernel/changelog/v2.5/42/
> Does this mean that the "trip points" don't work with the 2.4.20 patched
> kernel and that's why the fan is on at the wrong time?

Not imo.  I wasn't sure what Pavel meant by "Fix thermal management", either,
but the R/W was specifically to allow someone to override the trip points.  I'm
not sure why that _should_ be included in Linux ACPI implementation, since it's
an open invitation to destroy your machine, but then we Linux geeks are supposed
to be smart enough to be trusted with such awesome power :-)

> Related acpi-support threads:
> http://sourceforge.net/mailarchive/forum.php?thread_id=2725927&forum_id=7803
> having the BIOS control the fan
>
> http://sourceforge.net/mailarchive/forum.php?thread_id=2713262&forum_id=7803
> SpeedStep settings
> My system was configured to "automatic" but is now configured to use
> "battery". The fan is still on at the following temperatures:
>
> emmajane@debian:~$ acpi -t
>      Thermal 1: ok, 51.0 degrees C
>      Thermal 2: ok, 46.0 degrees C
>
> Does anyone know if this is because I'm using an old kernel + patch? Or is
> there something else I've missed?

I don't think there's anything wrong with the fan itself.  Does it really come
on when the thermal trip points say it should?  Then the acpi implementation
works :-)  Whether the laptop maker has done a good job of defining the trip
points is another matter, but I'd rather trust them than risk my machine.

derek



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