Set minimum fan speed on Fujitsu/Kontron motherboards with Teutates BMC

min_duty_cycle_settei.sh

#!/bin/bash

# Copyright (C) 2020 Kia
# Licensed under Zero Clause BSD License


if [[ $# -ne 3 ]]; then
    echo "usage: $0 (BMC I2C BUS NUMBER) (FAN PAGE) (DUTY CYCLE FLOOR)"
    echo ""
    echo "BMC I2C BUS NUMBER can be found as follows"
    echo "$ ls /sys/bus/i2c/devices/*/hwmon/hwmon*/fan1_input"
    echo ""
    echo "if the output of that command is:"
    echo "/sys/bus/i2c/devices/7-0073/hwmon/hwmon4/fan1_input"
    echo "that means that the I2C bus number is 7"
    echo "Check /sys/module/ftsteutates/drivers/i2c\:ftsteutates/ to be sure"
    echo ""
    echo "FAN PAGE = 0x48 + index of fan"
    echo "On my system, FAN PAGE can be (0x48, 0x49, 0x4a, 0x4b)"
    echo ""
    echo "DUTY CYCLE FLOOR can be any number from 0 to 255, but please"
    echo "don't set it lower than it already is."
    echo ""
    echo "This tool asks the Teutates BMC (in a way that does not survive"
    echo "reboots/power-cycles/shutdowns) to keep the PWM waveform that is"
    echo "fed to the fan corresponding to FAN PAGE to have a duty cycle that"
    echo "is greater or equal to (DUTY CYCLE FLOOR) / 255"
    echo ""
    echo "A fan that runs at MAX_RPM without a PWM signal (or with a DC PWM"
    echo "signal) will never run slower than MAX_RPM * (DUTY CYCLE FLOOR) / 255"
    echo ""
    echo "#########################################################################"
    echo "                               ☢CAUTION!!☢"
    echo "The supplied I2C bus number MUST correspond to the bus where the"
    echo "Teutates BMC lives on."
    echo ""
    echo "The supplied fan page must be between 0x48-0x4f inclusive and"
    echo "must correspond to a fan in your system connected to the Teutates BMC."
    echo ""
    echo "Incorrectly specifying the I2C bus number or fan page may BRICK"
    echo "or IRREVERSIBLY DESTROY your system!"
    echo "                               ☢CAUTION!!☢"
    echo "#########################################################################"
    echo ""
    echo "It is likely that this tool will not produce expected results if"
    echo "SilentFanConfig-Manager has been run -- which writes fan config stuff"
    echo "into nonvolatile storage. The aforementioned fan config stuff might"
    echo "set a different set of control modes, causing the write to 0x86 to"
    echo "not have the desired effect. I don't have the full Teutates"
    echo "documentation, so i do not know any of the control laws are."
    echo ""
    echo "However, if you have access to SilentFanConfig-Manager, why do you even"
    echo "need this?"
    echo ""
    echo "This tool has only been tested on a single motherboard:"
    echo "FUJITSU /D3641-S1, BIOS V5.0.0.13 R1.7.0 for D3641-S1x"
    echo "with FTS Teutates chip revision: 3.11"
    echo ""
    echo "FOR USE ONLY ON FUJITSU/KONTRON MOTHERBOARDS WITH TEUTATES BMC"
    echo ""
    exit 1
fi



case $2 in
    0x48|0x49|0x4a|0x4b|0x4c|0x4d|0x4e|0x4f)
        echo "supplied fan page is "$2
        ;;
    *)
        echo "INVALID FAN PAGE!!"
        exit 2
        ;;
esac




set -e

echo -n "Testing for Teutates BMC presence... "
# test that we have a teutates bmc, ideally this modprobe fails otherwise
sudo modprobe ftsteutates
# but we need it not be loaded, so we can have the i2c bus to ourselves
sudo rmmod ftsteutates

echo "present"
# this lets us do i2cset
sudo modprobe i2c-dev

# switch the page for the fan in question. the user is responsible
# for making sure this is between 0x48 and 0x4f
echo "writing to the i2c bus; hope you gave us the correct one!"
sudo i2cset -y $1 0x73 0x7f $2

# set PWM duty cycle
sudo i2cset -y $1 0x73 0x86 $3

# set the page back to 0x00 just to be kind to whoever (the kernel module) talks with the BMC after us
sudo i2cset -y $1 0x73 0x7f 0x00

echo "writes done"
# let us look at our handiwork via sensors(1).
# be patient, i think the BMC only updates RPM every second or so
sudo modprobe ftsteutates

@totalizator : What happens if you write '255' to the duty cycle register? Do the fans spin up? If yes - the BMC might just pick a fan speed above the "minimum" duty cycle specified in the 0x86 register - which is very much plausible, the script controls the minimum fan speed and not the actual fan speed.

If it doesn't work - are you sure that you are using 4-pin PWM fans (and not 3-pin fans? Not sure if the board supports voltage regulation).

I'd love to have more control over the fan speed and potentially also be able to fully turn them off, but for that, someone would need to find more documentation about the Teutates chip :).
I asked the Kontron support about this, but unfortunately, they don't respond to inquiries from private customers. You could try asking the supplier that you bought the board from if they are able to provide additional documentation about the hardware, maybe anyone is more successful at this than I am...