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xerxes: use dynamic hwmon discovery for fan control
author
lassulus
date
(Jan 15, 2026, 11:02 PM CET)
commit
1b686897
1b686897b675a45a4f199094156e5b87ed6d3a4b
parent
33065862
330658622f48bee1cafa5d215afcc980834ea37f
+75
-17
+75
-17
machines/xerxes/gpd-fan.nix
+75
-17
machines/xerxes/gpd-fan.nix
···
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{ pkgs, ... }:
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let
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# Find hwmon device by name and return path to specific file
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# Usage: findHwmon "k10temp" "temp1_input" -> /sys/class/hwmon/hwmonX/temp1_input
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gpd-fan-control = pkgs.writeShellScript "gpd-fan-control" ''
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set -euo pipefail
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# Configuration
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INTERVAL=2
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MINTEMP=55000 # millidegrees - fan off below this
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MAXTEMP=90000 # millidegrees - fan full above this
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MINPWM=0
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MAXPWM=255
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# Find hwmon paths by name
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find_hwmon() {
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local name=$1
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for hwmon in /sys/class/hwmon/hwmon*; do
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if [[ -f "$hwmon/name" ]] && [[ "$(cat "$hwmon/name")" == "$name" ]]; then
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echo "$hwmon"
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return 0
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fi
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done
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echo "ERROR: hwmon device '$name' not found" >&2
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return 1
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}
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FAN_HWMON=$(find_hwmon "gpdfan")
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TEMP_HWMON=$(find_hwmon "k10temp")
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PWM_FILE="$FAN_HWMON/pwm1"
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PWM_ENABLE="$FAN_HWMON/pwm1_enable"
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TEMP_FILE="$TEMP_HWMON/temp1_input"
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echo "Fan control: $PWM_FILE"
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echo "Temperature: $TEMP_FILE"
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# Enable manual PWM control
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echo 1 > "$PWM_ENABLE"
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cleanup() {
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echo "Restoring automatic fan control..."
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echo 0 > "$PWM_ENABLE" 2>/dev/null || true
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}
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trap cleanup EXIT
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while true; do
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TEMP=$(cat "$TEMP_FILE")
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if (( TEMP <= MINTEMP )); then
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PWM=$MINPWM
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elif (( TEMP >= MAXTEMP )); then
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PWM=$MAXPWM
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else
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# Linear interpolation
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PWM=$(( (TEMP - MINTEMP) * (MAXPWM - MINPWM) / (MAXTEMP - MINTEMP) + MINPWM ))
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fi
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echo "$PWM" > "$PWM_FILE"
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sleep "$INTERVAL"
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done
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'';
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in
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{
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# Load modules in explicit order for stable hwmon numbering
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# gpd_fan -> hwmon2, k10temp -> hwmon3 (loaded before ACPI devices)
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boot.kernelModules = [
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"gpd_fan"
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"k10temp"
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];
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hardware.fancontrol = {
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enable = true;
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config = ''
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INTERVAL=2
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DEVPATH=hwmon2=devices/platform/gpd_fan hwmon3=devices/pci0000:00/0000:00:18.3
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DEVNAME=hwmon2=gpdfan hwmon3=k10temp
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FCTEMPS=hwmon2/pwm1=hwmon3/temp1_input
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FCFANS=hwmon2/pwm1=hwmon2/fan1_input
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MINTEMP=hwmon2/pwm1=45
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MAXTEMP=hwmon2/pwm1=85
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MINSTART=hwmon2/pwm1=40
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MINSTOP=hwmon2/pwm1=30
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MINPWM=hwmon2/pwm1=0
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MAXPWM=hwmon2/pwm1=255
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'';
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# Disable the built-in fancontrol (it uses brittle hwmon numbers)
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hardware.fancontrol.enable = false;
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systemd.services.gpd-fan-control = {
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description = "GPD Fan Control (dynamic hwmon discovery)";
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wantedBy = [ "multi-user.target" ];
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after = [ "systemd-modules-load.service" ];
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serviceConfig = {
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ExecStart = gpd-fan-control;
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Restart = "always";
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RestartSec = 5;
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};
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};
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}