#!/bin/sh
# diskOS dev/recovery: USB CDC-ACM serial console on the device USB-C port.
# Host enumerates 0525:a4a7 -> /dev/ttyACM0 -> root shell (raw, no login).
#
# Robust against the failure that killed the previous attempt: the stock
# serial_config.sh binds the UDC exactly once and never retries, so a UDC that
# registers (or a host that plugs in) a moment later was missed. This runs a
# persistent supervisor: (re)bind whenever a UDC is present, keep a shell alive
# on ttyGS0. All steps best-effort + logged to a persistent (rw) partition.

LOG=/usr/data/fiio/usbserial.log
G=/sys/kernel/config/usb_gadget/serial_demo

log() { echo "$(date 2>/dev/null) $*" >> "$LOG" 2>/dev/null; }

build_gadget() {
	[ -d /sys/kernel/config/usb_gadget ] || mount -t configfs none /sys/kernel/config 2>/dev/null
	[ -d "$G" ] && return 0
	mkdir -p "$G" || return 1
	echo 0x0525 > "$G/idVendor"
	echo 0xa4a7 > "$G/idProduct"
	echo 0x0200 > "$G/bcdUSB"
	echo 0x2400 > "$G/bcdDevice"
	echo 0x02   > "$G/bDeviceClass"
	echo 0x00   > "$G/bDeviceSubClass"
	echo 0x00   > "$G/bDeviceProtocol"
	mkdir -p "$G/strings/0x409"
	echo "INGENIC"       > "$G/strings/0x409/manufacturer"
	echo "diskOS Serial" > "$G/strings/0x409/product"
	echo "diskos-serial" > "$G/strings/0x409/serialnumber"
	mkdir -p "$G/configs/c.1/strings/0x409"
	echo 120  > "$G/configs/c.1/MaxPower"
	echo 0x80 > "$G/configs/c.1/bmAttributes"
	echo "serial" > "$G/configs/c.1/strings/0x409/configuration"
	mkdir -p "$G/functions/acm.0"
	ln -sf "$G/functions/acm.0" "$G/configs/c.1/" 2>/dev/null
	log "gadget built"
}

# Best-effort nudge into peripheral mode. dr_mode=otg already auto-switches to
# device when plugged into a host (CC/pin), so this is only a safety net. Only
# the unambiguous "device" token is written -- never anything that could select
# host mode and break enumeration.
force_device_mode() {
	for f in /sys/devices/platform/*otg*/dwc2_mode \
	         /sys/devices/platform/*otg*/dwc2_force_dr_mode \
	         /sys/devices/platform/*/13500000.otg/dwc2_mode; do
		[ -e "$f" ] || continue
		echo device > "$f" 2>/dev/null && log "wrote device-mode to $f"
	done
}

bound() { [ -n "$(cat "$G/UDC" 2>/dev/null)" ]; }

bind_when_ready() {
	udc=$(ls /sys/class/udc/ 2>/dev/null | head -n1)
	[ -n "$udc" ] || return 1
	echo "$udc" > "$G/UDC" 2>/dev/null && { log "bound UDC=$udc"; return 0; }
	return 1
}

# Delegate the ttyGS0 shell to diskos-debug (the SINGLE owner - fuser-guarded + self-respawning).
# Two independent shell respawners on one tty is the classic "answers once then goes silent" wedge,
# so this script no longer binds its own shell; it only builds the gadget and asks diskos-debug to
# attach the one shell. Idempotent: serial-on is a no-op if a shell already owns ttyGS0.
DEBUG=/usr/project/diskos-debug.sh
ensure_shell() {
	[ -c /dev/ttyGS0 ] || return 0
	[ -x "$DEBUG" ] && "$DEBUG" serial-on >/dev/null 2>&1
}

main() {
	: > "$LOG" 2>/dev/null
	log "S99usbserial start"
	build_gadget
	force_device_mode
	while true; do
		bound || bind_when_ready
		ensure_shell
		sleep 2
	done
}

case "$1" in
	start) main & ;;
	*) exit 1 ;;
esac
exit 0