pwmconfig assumes no fan control from fans not stopping

Bug #1155107 reported by charonme on 2013-03-14
This bug affects 1 person
Affects Status Importance Assigned to Milestone
lm-sensors (Ubuntu)

Bug Description

pwmconfig attempts to stop fans to determine whether it's possible to control fan speed. If fans don't respond to the stopping signal, pwmconfig assumes it's not possible to control the fans. However some motherboards or BIOS configurations seem to protect the fans from stopping, but it's still possible to set non-zero fan speeds. For example after sudo su I was able to echo 20 > /sys/class/hwmon/hwmon2/device/pwm1 which set a very slow fan speed and echo 120 > /sys/class/hwmon/hwmon2/device/pwm1 set a much higher speed - so obviously fan speed is working perfectly at least in this range. However if I try to set a very low value (between 0 and 17) the fan speeds up probably as a result of the mainboard or BIOS protection.

pwmconfig should take into account that sometimes (on some mobos or bioses) fan speed control is only possible in some range of speeds and/or stopping the fans is not always possible even though fan control works

Phillip Susi (psusi) wrote :

Are you sure it actually speeds up when you set it too low? I have noticed that the Intel stock CPU fans seem to have a minimum speed they will refuse to go below, but when you try, it just refuses to go any lower rather than speeding up.

charonme (charonme) wrote :

Good question, so I tested the fan (Arctic Cooling F14 PWM) on a different mobo and it really seems the anti-stopping protection is indeed in the fan. But the fan really speeds up briefly when I try to stop it

Robie Basak (racb) wrote :

Thank you for taking the time to report this bug and helping to make Ubuntu better.

It sounds like this would need fundamental changes to pwmconfig to detect and fix. This would best be reported and addressed in the upstream lm-sensors project, rather than in Ubuntu directly. Are you able to report it there, please?

Changed in lm-sensors (Ubuntu):
importance: Undecided → Medium
charonme (charonme) wrote :

Sure, I just didn't know where to report this and this is the only place I found :)

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