#!/bin/ibash
# Write the address for the LCD panel to repair brightness hotkey. Underlying
# bug: https://bugs.freedesktop.org/show_bug.cgi?id=45452
# brightness bug on Ubuntu: https://bugs.launchpad.net/bugs/806032
#
# Author: Peter Lekensteyn <lekensteyn@gmail.com>
# This script is released into public domain, do whatever you want with it

set -e
modprobe acpi_call
if ! [ -f /proc/acpi/call ]; then
	echo "Could not load acpi_call. If not installed, get it from"
	echo "https://github.com/Bumblebee-Project/acpi_call"
	exit 1
fi
if ! type xxd &>/dev/null; then
	echo "Cannot find xxd program for hex to bin conversion"
	exit 1
fi
if ! [ -w /dev/mem ]; then
	echo "Cannot write to memory"
	exit 1
fi

# retrieve base address of Intel OpRegion
echo '\ASLB' > /proc/acpi/call
base=$(cat /proc/acpi/call)
if ! [ "${base:0:2}" = "0x" ]; then
	echo "\ASLB field not found, cannot retrieve base address"
	exit 1
fi

# Currently Active Display Devices List (CADL) is fixed at 0x160, see
# http://intellinuxgraphics.org/ACPI_IGD_OpRegion_%20Spec.pdf
addr=$((base+0x160))

# look for the LCD device handle, e.g. \_SB.PCI0.GFX0.LCD0
handle=$(grep -m 1 -h LCD /sys/bus/acpi/drivers/video/*/*/path)
if [ -z "$handle" ]; then
	echo "No LCD ACPI handle found"
	exit 1
fi

# Get ID for LCD device
echo "$handle._ADR" > /proc/acpi/call
disp=$(cat /proc/acpi/call)
if ! [ "${base:0:2}" = "0x" ]; then
	echo "Invalid LCD ID"
	exit 1
fi

# strip 0x
disp=${disp:2}
# make sure the length is a multiple of two, i.e. 0400 instead of 400
case ${#disp} in *[13579]) disp=0$disp ;; esac

# since we have a DWORD here (32-bit number), insert padding
disp_endian=00000000
# little-endian, 0400 must be written as 0004
for ((i=0; i<${#disp}; i+=2)); do
	disp_endian="${disp:i:2}$disp_endian"
done

echo 0x${disp_endian:0:8} | xxd -r | dd of=/dev/mem bs=1 seek=$addr count=4