Hi, i try to install this script:
Backlight is always at full brightness after a reboot with amdgpu driver
https://wiki.archlinux.org/index.php/backlight#Backlight_is_always_at_full_brightness_after_a_reboot_with_amdgpu_driver
fix-brightness.sh is placed in my home folder, with the change with my own hardware that i found in folder /var/lib/systemd/backlight:
#! /bin/bash
# Change the line below according to your hardware
BRIGHTNESS_FILE="/var/lib/systemd/backlight/pci-0000:04:00.0:backlight:amdgpu_bl0"
BRIGHTNESS=$(cat "$BRIGHTNESS_FILE")
BRIGHTNESS=$(($BRIGHTNESS*255/65535))
BRIGHTNESS=${BRIGHTNESS/.*} # truncating to int, just in case
echo $BRIGHTNESS > "$BRIGHTNESS_FILE"
Then i place fix-brightness.service in /etc/systemd/system/:
[Unit]
Description=Convert 16-bit brightness values to 8-bit before systemd-backlight applies it
Before=systemd-backlight@backlight:amdgpu_bl0.service
[Service]
Type=oneshot
ExecStart=/home/user/fix-brightness.sh
[Install]
WantedBy=multi-user.target
Then i do this in root terminal:
systemctl start fix-brightness.service
systemctl enable fix-brightness.service
After reboot the brightness is back to 100% 
, then i do this:
systemctl status systemd-backlight@backlight:amdgpu_bl0.service
The service start correct, but now it say “0 is to low for brightness, try to 2”.
Then i going to this file:
/var/lib/systemd/backlight/pci-0000:04:00.0:backlight:amdgpu_bl0
and set manually 0 in 2 (with root), but after reboot its again to 0! How can this be? What im doing wrong?