Switch LG 45GX950A input on Linux

switch-input

#!/usr/bin/env python3
"""Switch LG 45GX950A input source via DDC alt mode.

System package dependencies:
    ddcutil    - detects the i2c bus (https://www.ddcutil.com)
    i2c-tools  - provides i2ctransfer for raw i2c writes

Run without root:
    sudo groupadd i2c
    sudo usermod -aG i2c $USER
    sudo sh -c 'echo KERNEL==\"i2c-[0-9]*\", GROUP=\"i2c\", MODE=\"0660\" > /etc/udev/rules.d/60-i2c.rules'
    sudo udevadm control --reload-rules
    sudo udevadm trigger
    newgrp i2c

Usage:
    switch-input dp
    switch-input hdmi1
    switch-input hdmi2
    switch-input usbc
"""

import re
import subprocess
import sys

INPUTS = {
    "hdmi1": 0x90,
    "hdmi2": 0x91,
    "dp":    0xD0,
    "usbc":  0xD1,
}


def find_lg_bus():
    result = subprocess.run(["ddcutil", "detect"], capture_output=True, text=True)
    bus = None
    for line in result.stdout.splitlines():
        m = re.search(r"/dev/i2c-(\d+)", line)
        if m:
            bus = m.group(1)
        if "mfg id" in line.lower() and "gsm" in line.lower():
            return bus
    sys.exit("Error: no LG monitor detected")


def send(bus, lo):
    reg, p0, p1, vcp, hi = 0x50, 0x84, 0x03, 0xF4, 0x00
    chk = 0x6E ^ reg ^ p0 ^ p1 ^ vcp ^ hi ^ lo
    cmd = ["i2ctransfer", "-y", str(bus), "w7@0x37",
           *[f"0x{b:02X}" for b in [reg, p0, p1, vcp, hi, lo, chk]]]
    subprocess.run(cmd, check=True)


if len(sys.argv) != 2 or sys.argv[1] not in INPUTS:
    print(f"Usage: {sys.argv[0]} [{' | '.join(INPUTS)}]")
    sys.exit(1)


send(find_lg_bus(), INPUTS[sys.argv[1]])