# [SOLVED] ACPI, trip_points: write error: Input/output error

## Joseph K.

My last niggling problem on this HP Compaq nx8220 is that the CPU fan doesn't turn on under load as I would expect it to, and I'm not sure what the hardware sensors are, if at all.  With acpi=off the CPU fan does turn on under load.

It's a Centrino system, the chipset is the Intel 915PM Express Chipset that has an 82801Fxx controller thingy.  The lm_sensors page has everything but F for the 82801.  My /proc/acpi directory has fan, processor, thermal_zones, etc with interesting stuff in them.  sensors-detect doesn't find anything.

What are the hardware sensors and how do I access them?

How do I configure the CPU fan to turn on at a certain temperature?

Thanks!

Edit: SolvedLast edited by Joseph K. on Mon Mar 24, 2008 10:32 am; edited 2 times in total

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## baeksu

AFAIR, lm_sensors do not take measurements from /proc/acpi (at least it never worked for me). So I don't think you can use sensors on a laptop.

You can cat the different files in /proc/acpi to get temperature and state readings for cpu and maybe other things, but I don't think you can control the fan from there.

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## Joseph K.

Yeah, I didn't think that lm_sensors used /proc/acpi, but I thought there might be some other package that is suitable.  If the BIOS can switch the fan on appropriately, I imagine there must be a script or something that can do the same thing by, I presume, reading from /proc/acpi (or /sys, I'm not sure).  Lots of people have a Centrino system, so I presume something is out there.

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## Joseph K.

OK, I'm getting somewhere.  I don't need lm_sensors it seems, since it's all ACPI.  I can check the temperature and turn the fans on and off via /proc/acpi/.  I tried to reconfigure the trip points via the advice in this Linux ACPI howto.  I thought the trip points were too high but on doing some research it seems they're fine.

The final (I think) hurdle is this, when in /proc/acpi/thermal_zone/TZ1:

```
nx8220 TZ1 # echo 100:90:35:45:55 > trip_points

-su: echo: write error: Input/output error
```

I've found bug reports on the web from other people with the same problem, but no solutions.   :Sad: 

If I can't solve this it's no big deal, but I'm very temperature conscious these days, so I would like to make the fans to kick in earlier.

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## baeksu

Can't you set the trip points from bios?

The reason I didn't think you can manipulate the fan at all from /proc/acpi was that I used to have one of the early Centrino models (bought in spring of 2003), and in that sending data into the files in /proc/acpi would fail with a similar i/o error you're getting.

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## Joseph K.

No, the BIOS configuration is extremely limited.  I was reading some lkml posts about the i/o error, it seems it may have worked in the past or something, I need to read further.

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## Joseph K.

<sigh> Now I know why it doesn't work, there is a summary here.

Now I wonder, is acpid suitable for manually overriding the trip points?

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