How to control panel brightness and backlight

Brightness

# valid range : 0x0FFF (dark) ~ 0x0000 (brightest) # highest 4 bits must be zero
# notice: keep highest 4 bits zero or brightness will be dark whatever lower 12 bits set

# use hexadecimal without leading "0x" (default:7FF)
BRIGHTNESS=6FF 
sudo i2cset -f -y 2 0x20 0x90 $(( $((16#$BRIGHTNESS)) / 256 )) $(( $((16#$BRIGHTNESS)) % 256 )) i

# keep setting
sudo i2cset -f -y 2 0x20 0xe8 0x01 0x78 0x45 0x56 i && sudo reboot