// SPDX-License-Identifier: GPL-2.0+
/*
* u_serial.c - utilities for USB gadget "serial port"/TTY support
*
* Copyright (C) 2003 Al Borchers (alborchers@steinerpoint.com)
* Copyright (C) 2008 David Brownell
* Copyright (C) 2008 by Nokia Corporation
*
* This code also borrows from usbserial.c, which is
* Copyright (C) 1999 - 2002 Greg Kroah-Hartman (greg@kroah.com)
* Copyright (C) 2000 Peter Berger (pberger@brimson.com)
* Copyright (C) 2000 Al Borchers (alborchers@steinerpoint.com)
*/
/* #define VERBOSE_DEBUG */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/module.h>
#include <linux/console.h>
#include <linux/kthread.h>
#include <linux/workqueue.h>
#include <linux/kfifo.h>
#include "u_serial.h"
/*
* This component encapsulates the TTY layer glue needed to provide basic
* "serial port" functionality through the USB gadget stack. Each such
* port is exposed through a /dev/ttyGS* node.
*
* After this module has been loaded, the individual TTY port can be requested
* (gserial_alloc_line()) and it will stay available until they are removed
* (gserial_free_line()). Each one may be connected to a USB function
* (gserial_connect), or disconnected (with gserial_disconnect) when the USB
* host issues a config change event. Data can only flow when the port is
* connected to the host.
*
* A given TTY port can be made available in multiple configurations.
* For example, each one might expose a ttyGS0 node which provides a
* login application. In one case that might use CDC ACM interface 0,
* while another configuration might use interface 3 for that. The
* work to handle that (including descriptor management) is not part
* of this component.
*
* Configurations may expose more than one TTY port. For example, if
* ttyGS0 provides login service, then ttyGS1 might provide dialer access