brightness-control.sh

#!/bin/bash

set -euo pipefail

i2c_from_output() {
    dir=$(ls -d /sys/bus/pci/devices/0000:03:00.0/drm/card*/card*-"$1"/i2c*)
    dev=$(basename "$dir")
    echo "/dev/$dev"
}

change_brightness() {
    brightness=$(ddccontrol -r 0x10 -W "$1" "dev:$(i2c_from_output DP-1)" | tail -n 1 | cut -d '/' -f 2)

    if grep -q enabled /sys/bus/pci/devices/0000:03:00.0/drm/card*/card*-DP-2/enabled; then
        ddccontrol -r 0x10 -w "$brightness" "dev:$(i2c_from_output DP-2)"
    fi
}

case $1 in
up)
    change_brightness +10
    ;;
down)
    change_brightness -10
    ;;
esac