#!/bin/sh
#
# Copyright 2023,2024 Emil Renner Berthing <emil.renner.berthing@canonical.com>
#
# This is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.

set -e

fs='/sys/kernel/config'
top="$fs/usb_gadget"

service='mkgadget'
ctrl='10100000.usb'
gadget=g1
vid=0x1b67
pid=0x400c

model="$(tr '\000' '\n' < /proc/device-tree/model)"
manufacturer="${model%% *}"
product="${model#* }"
serial=0001

c1_name='Ethernet Emulation'
dev_addr='56:7f:82:61:f4:0a'
host_addr='92:94:d9:a4:92:9a'

readonly usage="
Usage: $0 [<options>] [add|del|enable|disable]

Options:
    -C <controller>  Use this UDC controller. Default: $ctrl
    -s <service>     Set systemd service name. Default: $service
    -g <gadget>      Set gadget name. Default: $gadget
    -V <vid>         Set vendor ID. Default: $vid
    -P <pid>         Set product ID. Default: $pid
    -m <name>        Set manufacturer string. Default: $manufacturer
    -p <name>        Set product string. Default: $product
    -c <config>      Set configuration name. Default: $c1_name
    -D <macaddr>     Set device MAC address. Default: $dev_addr
    -H <macaddr>     Set host MAC address. Default: $host_addr
    -h               Show this help.
"

while getopts 'C:s:g:V:P:m:p:c:D:H:h' opt; do
  case "$opt" in
  C) ctrl="$OPTARG";;
  s) service="$OPTARG";;
  g) gadget="$OPTARG";;
  V) vid="$OPTARG";;
  P) pid="$OPTARG";;
  m) manufacturer="$OPTARG";;
  p) product="$OPTARG";;
  c) c1_name="$OPTARG";;
  D) dev_addr="$OPTARG";;
  H) host_addr="$OPTARG";;
  h)
    echo "Create USB gadget on $ctrl"
    echo "$usage"
    exit 0;;
  *)
    echo "$usage" >&2
    exit 1;;
  esac
done
shift $((OPTIND - 1))

error() {
  echo "$@" >&2
  exit 1
}

case "$1" in
on|add|create)
  modprobe libcomposite || error "Error loading libcomposite: $?"
  for i in /sys/class/udc/$ctrl; do
    if [ -d "$i" ]; then
      udc="${i#/sys/class/udc/}"
      break
    fi
  done
  [ -n "$udc" ] || error "Could not find UDC controller $ctrl"
  [ -d "$top" ] || error "Could not find $top"
  [ ! -d "$top/$gadget" ] || error "Gadget $gadget already exists"

  # Create gadget
  mkdir "$top/$gadget"
  cd "$top/$gadget"

  # Set VID/PID
  echo "$vid" > idVendor
  echo "$pid" > idProduct

  # English language strings
  mkdir strings/0x409
  echo "$manufacturer" > strings/0x409/manufacturer
  echo "$product" > strings/0x409/product
  echo "$serial" > strings/0x409/serialnumber

  # Create EEM configuration
  mkdir configs/c.1
  mkdir configs/c.1/strings/0x409
  echo "$c1_name" > configs/c.1/strings/0x409/configuration
  mkdir functions/eem.0
  echo "$host_addr" > functions/eem.0/host_addr
  echo "$dev_addr" > functions/eem.0/dev_addr
  ln -s functions/eem.0 configs/c.1/

  # Enable new configuration for the USB controller
  echo "$udc" > UDC

  # Make sure device is in peripheral mode
  if [[ -f "/sys/class/udc/$udc/device/mode" ]]; then
    read -r mode < "/sys/class/udc/$udc/device/mode"
    case "$mode" in
    *_peripheral) ;;
    *) echo peripheral > "/sys/class/udc/$udc/device/mode";;
    esac
  fi
  ;;
off|del|delete|rm|remove)
  [ -d "$top/$gadget" ] || error "Gadget $gadget does not exist"
  cd "$top"

  # Disable gadget
  echo > "$gadget/UDC"
  # Remove function links
  for i in "$gadget"/configs/*/*; do
    [ ! -h "$i" ] || rm "$i"
  done
  # Remove functions
  for i in "$gadget"/functions/*; do
    [ ! -d "$i" ] || rmdir "$i"
  done
  # Remove configs
  for i in "$gadget"/configs/*; do
    [ ! -d "$i/strings/0x409" ] || rmdir "$i/strings/0x409"
    [ ! -d "$i" ] || rmdir "$i"
  done
  # Remove gadget
  rmdir "$gadget/strings/0x409"
  rmdir "$gadget"
  ;;
enable)
  if [ ! -f "/etc/systemd/system/${service}.service" ]; then
    {
      echo '[Unit]'
      echo 'Description=Create USB EEM gadget'
      echo 'DefaultDependencies=no'
      echo
      echo '[Service]'
      echo 'Type=oneshot'
      echo 'RemainAfterExit=yes'
      echo 'StandardInput=null'
      echo 'ProtectSystem=full'
      echo 'ProtectHome=yes'
      echo "ExecStart=$0 add"
      echo "ExecStop=$0 del"
      echo
      echo '[Install]'
      echo 'WantedBy=usb-gadget.target'
    } | install -m644 -o root -g root /dev/stdin "/etc/systemd/system/${service}.service"
    echo "Created \"/etc/systemd/system/${service}.service\""
  fi
  systemctl enable "${service}.service"
  ;;
disable)
  systemctl disable "${service}.service"
  rm "/etc/systemd/system/${service}.service"
  echo "Removed \"/etc/systemd/system/${service}.service\""
  ;;
*)
  echo "Unknown action \"$1\"." >&2
  echo "$usage" >&2
  exit 1;;
esac