#!/bin/bash

# https://www.kernel.org/doc/html/latest/hwmon/it87.html
# https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2cbb9c370fe32b5de5243f7338dc6ce8747d495b

set -eux

modprobe it87

CT="$(grep -l coretemp /sys/class/hwmon/hwmon*/name | head -n1 | xargs dirname)/temp1_input"
cd "$(grep -l it8792 /sys/class/hwmon/hwmon*/name | head -n1 | xargs dirname)"

grep . pwm1* temp1*

# automatic fan control - the chip seems to ignore these settings
#echo 2          > pwm1_enable                  # automatic mode
#echo 1          > pwm1_auto_channels_temp      # temperature channel
#echo 127000     > pwm1_auto_point1_temp_hyst   # ??
#echo 127000     > pwm1_auto_point1_temp        # fan off temp
#echo 127000     > pwm1_auto_point2_temp        # fan start temp
#echo 127000     > pwm1_auto_point3_temp        # fan max temperature
#echo 100        > pwm1_auto_start              # start pwm value
#echo 0          > pwm1_auto_slope              # pwm slope, 1/8th pwm

# manual fan control - magic incantation
echo 1          > pwm1_enable                   # manual mode
echo 200000     > pwm1_freq                     # quieter fan
echo 0          > temp3_type                    # disabled unused sensor
echo 4          > temp1_type                    # switch sensor to thermistor
sleep 1                                         # wait for driver to write to chip
echo 0          > temp1_type                    # disable the sensor
echo 42         > pwm1                          # set the fan speed

grep . *pwm1* temp1*

set +x
OLDPWM="$(cat pwm1)"
while sleep 1; do
    TEMPC="$(cat "$CT")"
    if [ "$TEMPC" -ge 85000 ]; then
        NEWPWM=255
    elif [ "$TEMPC" -ge 80000 ]; then
        NEWPWM=180
    elif [ "$TEMPC" -ge 60000 ]; then
        NEWPWM=130
    else
        NEWPWM=100
    fi
    if [ "$OLDPWM" -ne "$NEWPWM" ]; then
        echo "Fan speed change: OLDPWM=$OLDPWM TEMPC=$TEMPC NEWPWM=$NEWPWM"
        echo "$NEWPWM" > pwm1
        OLDPWM="$NEWPWM"
        sleep 30
    fi
done