Workaround for oled backlight issues

README.md

Works for Thinkpad X1 Yoga 2G (20JDCTO1WW) (and most probably others) with OLED display

First install inotify-tools. Then create a script around inotify that will be launched upon each boot or through autostart.

sudo apt install inotify-tools
cat <<-EO1 | sudo tee /usr/local/bin/xbacklightmon.sh#!/bin/bash
    # https://wiki.archlinux.org/index.php/backlight#sysfs_modified_but_no_brightness_change
    # https://wiki.archlinux.org/index.php/Alienware_13#OLED_screen_brightness
    # https://gist.github.com/lalten/ce5ac0b1cc4b24a24cc44926255b871d
    # apt install inotify-tools 

    path=/sys/class/backlight/intel_backlight

    luminance() {
        read -r level < "$path"/actual_brightness
        new_brightness="$(bc -l <<< "scale = 2; $level / $max")"
        LC_NUMERIC="en_US.UTF-8" printf '%f\n' $new_brightness
    }

    read -r max < "$path"/max_brightness

    xrandr --output eDP-1 --brightness "$(luminance)"

    inotifywait -me modify --format '' "$path"/actual_brightness | while read; do
        xrandr --output eDP-1 --brightness "$(luminance)"
    done

EO1
sudo chmod +x /usr/local/bin/xbacklightmon.sh

cat <<-EO2 >~/.config/autostart/xbacklightmon.desktop
    [Desktop Entry]
    Type=Application
    Exec=/usr/local/bin/xbacklightmon.sh
    Hidden=false
    X-GNOME-Autostart-enabled=true
    Name=xbacklightmon
EO2

xbacklightmon.sh

#!/bin/bash
# Make Oled brightness work for Thinkpad X1 Yoga
# apt install inotify-tools 

# https://wiki.archlinux.org/index.php/backlight#sysfs_modified_but_no_brightness_change
# https://wiki.archlinux.org/index.php/Alienware_13#OLED_screen_brightness
# https://gist.github.com/lalten/ce5ac0b1cc4b24a24cc44926255b871d

path=/sys/class/backlight/intel_backlight

luminance() {
    read -r level < "$path"/actual_brightness
    new_brightness="$(bc -l <<< "scale = 2; $level / $max")"
    LC_NUMERIC="en_US.UTF-8" printf '%f\n' $new_brightness
}

read -r max < "$path"/max_brightness

xrandr --output eDP-1 --brightness "$(luminance)"

inotifywait -me modify --format '' "$path"/actual_brightness | while read; do
    xrandr --output eDP-1 --brightness "$(luminance)"
done

Note that this doesn't work well together with Gnome's Night Light.
Here's a function that reads the current gamma settings from xrandr, so they can be reapplied when setting brightness:

gamma() {
    # read and invert gamma values, see https://gitlab.freedesktop.org/xorg/app/xrandr/issues/33
    gammas_inverted=$(xrandr --verbose | awk '/Gamma/ {print $2; exit}')
    IFS=':' read -r r g b <<< "$gammas_inverted"
    r=$(bc -l <<< "1/$r")
    g=$(bc -l <<< "1/$g")
    b=$(bc -l <<< "1/$b")
    LC_NUMERIC="en_US.UTF-8" printf '%f:%f:%f\n' $r $g $b
}

xrandr --output eDP-1 --brightness "$(luminance)" --gamma "$(gamma)"

Unfortunately, Night Light seems to do more than just adjust gamma so reapplying these values will look really bad.