path: root/drivers/usb/gadget/function/u_serial.c

// 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
 * for a telephone or fax link.  And ttyGS2 might be something that just
 * needs a simple byte stream interface for some messaging protocol that
 * is managed in userspace ... OBEX, PTP, and MTP have been mentioned.
 *
 *
 * gserial is the lifecycle interface, used by USB functions
 * gs_port is the I/O nexus, used by the tty driver
 * tty_struct links to the tty/filesystem framework
 *
 * gserial <---> gs_port ... links will be null when the USB link is
 * inactive; managed by gserial_{connect,disconnect}().  each gserial
 * instance can wrap its own USB control protocol.
 *	gserial->ioport == usb_ep->driver_data ... gs_port
 *	gs_port->port_usb ... gserial
 *
 * gs_port <---> tty_struct ... links will be null when the TTY file
 * isn't opened; managed by gs_open()/gs_close()
 *	gserial->port_tty ... tty_struct
 *	tty_struct->driver_data ... gserial
 */

/* RX and TX queues can buffer QUEUE_SIZE packets before they hit the
 * next layer of buffering.  For TX that's a circular buffer; for RX
 * consider it a NOP.  A third layer is provided by the TTY code.
 */
#define QUEUE_SIZE		16
#define WRITE_BUF_SIZE		8192		/* TX only */
#define GS_CONSOLE_BUF_SIZE	8192

/* console info */
struct gs_console {
	struct console		console;
	struct work_struct	work;
	spinlock_t		lock;
	struct usb_request	*req;
	struct kfifo		buf;
	size_t			missed;
};

/*
 * The port structure holds info for each port, one for each minor number
 * (and thus for each /dev/ node).
 */
struct gs_port {
	struct tty_port		port;
	spinlock_t		port_lock;	/* guard port_* access */

	struct gserial		*port_usb;
#ifdef CONFIG_U_SERIAL_CONSOLE
	struct gs_console	*console;
#endif

	u8			port_num;

	struct list_head	read_pool;
	int read_started;
	int read_allocated;
	struct list_head	read_queue;
	unsigned		n_read;
	struct delayed_work	push;

	struct list_head	write_pool;
	int write_started;
	int write_allocated;
	struct kfifo		port_write_buf;
	wait_queue_head_t	drain_wait;	/* wait while writes drain */
	bool                    write_busy;
	wait_queue_head_t	close_wait;
	bool			suspended;	/* port suspended */
	bool			start_delayed;	/* delay start when suspended */

	/* REVISIT this state ... */
	struct usb_cdc_line_coding port_line_coding;	/* 8-N-1 etc */
};

static struct portmaster {
	struct mutex	lock;			/* protect open/close */
	struct gs_port	*port;
} ports[MAX_U_SERIAL_PORTS];

#define GS_CLOSE_TIMEOUT		15		/* seconds */



#ifdef VERBOSE_DEBUG
#ifndef pr_vdebug
#define pr_vdebug(fmt, arg...) \
	pr_debug(fmt, ##arg)
#endif /* pr_vdebug */
#else
#ifndef pr_vdebug
#define pr_vdebug(fmt, arg...) \
	({ if (0) pr_debug(fmt, ##arg); })
#endif /* pr_vdebug */
#endif

/*-------------------------------------------------------------------------*/

/* I/O glue between TTY (upper) and USB function (lower) driver layers */

/*
 * gs_alloc_req
 *
 * Allocate a usb_request and its buffer.  Returns a pointer to the
 * usb_request or NULL if there is an error.
 */
struct usb_request *
gs_alloc_req(struct usb_ep *ep, unsigned len, gfp_t kmalloc_flags)
{
	struct usb_request *req;

	req = usb_ep_alloc_request(ep, kmalloc_flags);

	if (req != NULL) {
		req->length = len;
		req->buf = kmalloc(len, kmalloc_flags);
		if (req->buf == NULL) {
			usb_ep_free_request(ep, req);
			return NULL;
		}
	}

	return req;
}
EXPORT_SYMBOL_GPL(gs_alloc_req);

/*
 * gs_free_req
 *
 * Free a usb_request and its buffer.
 */
void gs_free_req(struct usb_ep *ep, struct usb_request *req)
{
	kfree(req->buf);
	usb_ep_free_request(ep, req);
}
EXPORT_SYMBOL_GPL(gs_free_req);

/*
 * gs_send_packet
 *
 * If there is data to send, a packet is built in the given
 * buffer and the size is returned.  If there is no data to
 * send, 0 is returned.
 *
 * Called with port_lock held.
 */
static unsigned
gs_send_packet(struct gs_port *port, char *packet, unsigned size)
{
	unsigned len;

	len = kfifo_len(&port->port_write_buf);
	if (len < size)
		size = len;
	if (size != 0)
		size = kfifo_out(&port->port_write_buf, packet, size);
	return size;
}

/*
 * gs_start_tx
 *
 * This function finds available write requests, calls
 * gs_send_packet to fill these packets with data, and
 * continues until either there are no more write requests
 * available or no more data to send.  This function is
 * run whenever data arrives or write requests are available.
 *
 * Context: caller owns port_lock; port_usb is non-null.
 */
static int gs_start_tx(struct gs_port *port)
/*
__releases(&port->port_lock)
__acquires(&port->port_lock)
*/
{
	struct list_head	*pool = &port->write_pool;
	struct usb_ep		*in;
	int			status = 0;
	bool			do_tty_wake = false;

	if (!port->port_usb)
		return status;

	in = port->port_usb->in;

	while (!port->write_busy && !list_empty(pool)) {
		struct usb_request	*req;
		int			len;

		if (port->write_started >= QUEUE_SIZE)
			break;

		req = list_entry(pool->next, struct usb_request, list);
		len = gs_send_packet(port, req->buf, in->maxpacket);
		if (len == 0) {
			wake_up_interruptible(&port->drain_wait);
			break;
		}
		do_tty_wake = true;

		req->length = len;
		list_del(&req->list);
		req->zero = kfifo_is_empty(&port->port_write_buf);

		pr_vdebug("ttyGS%d: tx len=%d, %3ph ...\n", port->port_num, len, req->buf);

		/* Drop lock while we call out of driver; completions
		 * could be issued while we do so.  Disconnection may
		 * happen too; maybe immediately before we queue this!
		 *
		 * NOTE that we may keep