USB gadget驱动框架（五）

本节主要分析虚拟串口的tty设备的注册、创建/dev/ttyGSx设备节点、tty相关接口的实现。

tty的申请与注册

源码：drivers/usb/gadget/function/u_serial.c

static const struct tty_operations gs_tty_ops = {
	.open =			gs_open,
	.close =		gs_close,
	.write =		gs_write,
	.put_char =		gs_put_char,
	.flush_chars =		gs_flush_chars,
	.write_room =		gs_write_room,
	.chars_in_buffer =	gs_chars_in_buffer,
	.unthrottle =		gs_unthrottle,
	.break_ctl =		gs_break_ctl,
};

static int userial_init(void)
{
	unsigned			i;
	int				status;

    //申请tty_driver驱动
	gs_tty_driver = alloc_tty_driver(MAX_U_SERIAL_PORTS);
	if (!gs_tty_driver)
		return -ENOMEM;

    //初始化tty_driver，设备节点名
	gs_tty_driver->driver_name = "g_serial";
	gs_tty_driver->name = "ttyGS";
	/* uses dynamically assigned dev_t values */

	gs_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
	gs_tty_driver->subtype = SERIAL_TYPE_NORMAL;
	gs_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
	gs_tty_driver->init_termios = tty_std_termios;

	/* 9600-8-N-1 ... matches defaults expected by "usbser.sys" on
	 * MS-Windows.  Otherwise, most of these flags shouldn't affect
	 * anything unless we were to actually hook up to a serial line.
	 */
	gs_tty_driver->init_termios.c_cflag =
			B9600 | CS8 | CREAD | HUPCL | CLOCAL;
	gs_tty_driver->init_termios.c_ispeed = 9600;
	gs_tty_driver->init_termios.c_ospeed = 9600;

    //tty_driver的tty_operations初始化
	tty_set_operations(gs_tty_driver, &gs_tty_ops);
	for (i = 0; i < MAX_U_SERIAL_PORTS; i++)
		mutex_init(&ports[i].lock);

	/* export the driver ... */
	status = tty_register_driver(gs_tty_driver);
	if (status) {
		pr_err("%s: cannot register, err %d\n",
				__func__, status);
		goto fail;
	}

	pr_debug("%s: registered %d ttyGS* device%s\n", __func__,
			MAX_U_SERIAL_PORTS,
			(MAX_U_SERIAL_PORTS == 1) ? "" : "s");

	return status;
fail:
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;
	return status;
}
module_init(userial_init);

static void userial_cleanup(void)
{
	tty_unregister_driver(gs_tty_driver);
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;
}
module_exit(userial_cleanup);

connect与disconnect

conect将会使能数据传输用的endpoint，同时启动数据数据的功能。

/**
 * gserial_connect - notify TTY I/O glue that USB link is active
 * @gser: the function, set up with endpoints and descriptors
 * @port_num: which port is active
 * Context: any (usually from irq)
 *
 * This is called activate endpoints and let the TTY layer know that
 * the connection is active ... not unlike "carrier detect".  It won't
 * necessarily start I/O queues; unless the TTY is held open by any
 * task, there would be no point.  However, the endpoints will be
 * activated so the USB host can perform I/O, subject to basic USB
 * hardware flow control.
 *
 * Caller needs to have set up the endpoints and USB function in @dev
 * before calling this, as well as the appropriate (speed-specific)
 * endpoint descriptors, and also have allocate @port_num by calling
 * @gserial_alloc_line().
 *
 * Returns negative errno or zero.
 * On success, ep->driver_data will be overwritten.
 */
int gserial_connect(struct gserial *gser, u8 port_num)
{
	struct gs_port	*port;
	unsigned long	flags;
	int		status;

	if (port_num >= MAX_U_SERIAL_PORTS)
		return -ENXIO;

	port = ports[port_num].port;
	if (!port) {
		pr_err("serial line %d not allocated.\n", port_num);
		return -EINVAL;
	}
	if (port->port_usb) {
		pr_err("serial line %d is in use.\n", port_num);
		return -EBUSY;
	}

	/* activate the endpoints */
	//使能in_endpoint，可用于in数据传输
	status = usb_ep_enable(gser->in);
	if (status < 0)
		return status;
	gser->in->driver_data = port;

    //使能out_endpoint，可用于out数据传输
	status = usb_ep_enable(gser->out);
	if (status < 0)
		goto fail_out;
	gser->out->driver_data = port;

	/* then tell the tty glue that I/O can work */
	spin_lock_irqsave(&port->port_lock, flags);
	gser->ioport = port;
	port->port_usb = gser;

	/* REVISIT unclear how best to handle this state...
	 * we don't really couple it with the Linux TTY.
	 */
	gser->port_line_coding = port->port_line_coding;

	/* REVISIT if waiting on "carrier detect", signal. */

	/* if it's already open, start I/O ... and notify the serial
	 * protocol about open/close status (connect/disconnect).
	 */
	//若当前TTYGSx设备节点已打开，则启动tx/rx的功能
	//并调用gserial的connect功能，详见drivers/usb/gadget/function/f_acm.c的acm_connect与acm_disconnect
	if (port->port.count) {
		pr_debug("gserial_connect: start ttyGS%d\n", port->port_num);
		gs_start_io(port);
		
		if (gser->connect)
			gser->connect(gser);
	} else {
		if (gser->disconnect)
			gser->disconnect(gser);
	}


	status = gs_console_connect(port_num);
	spin_unlock_irqrestore(&port->port_lock, flags);

	return status;

fail_out:
	usb_ep_disable(gser->in);
	return status;
}
EXPORT_SYMBOL_GPL(gserial_connect);

/**
 * gserial_disconnect - notify TTY I/O glue that USB link is inactive
 * @gser: the function, on which gserial_connect() was called
 * Context: any (usually from irq)
 *
 * This is called to deactivate endpoints and let the TTY layer know
 * that the connection went inactive ... not unlike "hangup".
 *
 * On return, the state is as if gserial_connect() had never been called;
 * there is no active USB I/O on these endpoints.
 */
void gserial_disconnect(struct gserial *gser)
{
	struct gs_port	*port = gser->ioport;
	unsigned long	flags;

	if (!port)
		return;

	/* tell the TTY glue not to do I/O here any more */
	spin_lock_irqsave(&port->port_lock, flags);

	/* REVISIT as above: how best to track this? */
	port->port_line_coding = gser->port_line_coding;

	port->port_usb = NULL;
	gser->ioport = NULL;
	if (port->port.count > 0 || port->openclose) {
		wake_up_interruptible(&port->drain_wait);
		if (port->port.tty)
			tty_hangup(port->port.tty);
	}
	spin_unlock_irqrestore(&port->port_lock, flags);

	/* disable endpoints, aborting down any active I/O */
	usb_ep_disable(gser->out);
	usb_ep_disable(gser->in);

	/* finally, free any unused/unusable I/O buffers */
	spin_lock_irqsave(&port->port_lock, flags);
	if (port->port.count == 0 && !port->openclose)
		kfifo_free(&port->port_write_buf);
	gs_free_requests(gser->out, &port->read_pool, NULL);
	gs_free_requests(gser->out, &port->read_queue, NULL);
	gs_free_requests(gser->in, &port->write_pool, NULL);

	port->read_allocated = port->read_started =
		port->write_allocated = port->write_started = 0;

	gs_console_disconnect(gser->in);
	spin_unlock_irqrestore(&port->port_lock, flags);
}
EXPORT_SYMBOL_GPL(gserial_disconnect);

gs_start_io

/**
 * gs_start_io - start USB I/O streams
 * @dev: encapsulates endpoints to use
 * Context: holding port_lock; port_tty and port_usb are non-null
 *
 * We only start I/O when something is connected to both sides of
 * this port.  If nothing is listening on the host side, we may
 * be pointlessly filling up our TX buffers and FIFO.
 */
static int gs_start_io(struct gs_port *port)
{
	struct list_head	*head = &port->read_pool;
	struct usb_ep		*ep = port->port_usb->out;
	int			status;
	unsigned		started;

	/* Allocate RX and TX I/O buffers.  We can't easily do this much
	 * earlier (with GFP_KERNEL) because the requests are coupled to
	 * endpoints, as are the packet sizes we'll be using.  Different
	 * configurations may use different endpoints with a given port;
	 * and high speed vs full speed changes packet sizes too.
	 */
	//申请out endpoint的req，最终会回调到udc驱动中usb_ep_ops的alloc_request
	//详见：drivers/usb/gadget/udc/s3c2410_udc.c
	status = gs_alloc_requests(ep, head, gs_read_complete,
		&port->read_allocated);
	if (status)
		return status;

	//申请in endpoint的req，最终会回调到udc驱动中usb_ep_ops的alloc_request
	//详见：drivers/usb/gadget/udc/s3c2410_udc.c
	status = gs_alloc_requests(port->port_usb->in, &port->write_pool,
			gs_write_complete, &port->write_allocated);
	if (status) {
		gs_free_requests(ep, head, &port->read_allocated);
		return status;
	}

	/* queue read requests */
	port->n_read = 0;
	started = gs_start_rx(port);

	if (started) {
		gs_start_tx(port);
		/* Unblock any pending writes into our circular buffer, in case
		 * we didn't in gs_start_tx() */
		tty_wakeup(port->port.tty);
	} else {
		gs_free_requests(ep, head, &port->read_allocated);
		gs_free_requests(port->port_usb->in, &port->write_pool,
			&port->write_allocated);
		status = -EIO;
	}

	return status;
}

static void gs_free_requests(struct usb_ep *ep, struct list_head *head,
							 int *allocated)
{
	struct usb_request	*req;

	while (!list_empty(head)) {
		req = list_entry(head->next, struct usb_request, list);
		list_del(&req->list);
		gs_free_req(ep, req);
		if (allocated)
			(*allocated)--;
	}
}

static int gs_alloc_requests(struct usb_ep *ep, struct list_head *head,
		void (*fn)(struct usb_ep *, struct usb_request *),
		int *allocated)
{
	int			i;
	struct usb_request	*req;
	//由于*allocated初始化为0，则默认申请req的数量为QUEUE_SIZE=16
	int n = allocated ? QUEUE_SIZE - *allocated : QUEUE_SIZE;

	/* Pre-allocate up to QUEUE_SIZE transfers, but if we can't
	 * do quite that many this time, don't fail ... we just won't
	 * be as speedy as we might otherwise be.
	 */
	for (i = 0; i < n; i++) {
		req = gs_alloc_req(ep, ep->maxpacket, GFP_ATOMIC);
		if (!req)
			return list_empty(head) ? -ENOMEM : 0;
		req->complete = fn;
		list_add_tail(&req->list, head);
		if (allocated)
			(*allocated)++;
	}
	return 0;
}

gs_start_rx与gs_start_tx

/*
 * Context: caller owns port_lock, and port_usb is set
 */
static unsigned gs_start_rx(struct gs_port *port)
/*
__releases(&port->port_lock)
__acquires(&port->port_lock)
*/
{
	struct list_head	*pool = &port->read_pool;
	struct usb_ep		*out = port->port_usb->out;

    //read_pool不为空
	while (!list_empty(pool)) {
		struct usb_request	*req;
		int			status;
		struct tty_struct	*tty;

		/* no more rx if closed */
		tty = port->port.tty;
		if (!tty)
			break;

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

        //从list链表中取出空闲的req
		req = list_entry(pool->next, struct usb_request, list);
		list_del(&req->list);
		req->length = out->maxpacket;

		/* drop lock while we call out; the controller driver
		 * may need to call us back (e.g. for disconnect)
		 */
		spin_unlock(&port->port_lock);
		//将取出的req插入到out endpoint 的queue中
		status = usb_ep_queue(out, req, GFP_ATOMIC);
		spin_lock(&port->port_lock);

		if (status) {
			pr_debug("%s: %s %s err %d\n",
					__func__, "queue", out->name, status);
			list_add(&req->list, pool);
			break;
		}
		port->read_started++;

		/* abort immediately after disconnect */
		if (!port->port_usb)
			break;
	}
	return port->read_started;
}

/*
 * 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;

        //从list中取出空闲的req
		req = list_entry(pool->next, struct usb_request, list);
		//将需发送的数据填充到req->buf中
		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, 0x%02x 0x%02x 0x%02x ...\n",
			  port->port_num, len, *((u8 *)req->buf),
			  *((u8 *)req->buf+1), *((u8 *)req->buf+2));

		/* 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 sending data for a while after
		 * the TTY closed (dev->ioport->port_tty is NULL).
		 */
		port->write_busy = true;
		spin_unlock(&port->port_lock);
		//将取出的req插入到in endpoint的queue尾部
		status = usb_ep_queue(in, req, GFP_ATOMIC);
		spin_lock(&port->port_lock);
		port->write_busy = false;

		if (status) {
			pr_debug("%s: %s %s err %d\n",
					__func__, "queue", in->name, status);
			list_add(&req->list, pool);
			break;
		}

		port->write_started++;

		/* abort immediately after disconnect */
		if (!port->port_usb)
			break;
	}

	if (do_tty_wake && port->port.tty)
		tty_wakeup(port->port.tty);
	return status;
}

rx/tx的complete
在udc驱动中endpoint对应的req完成后，将会回调其complete函数，完成后续的动作。

static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
{
	struct gs_port	*port = ep->driver_data;

	/* Queue all received data until the tty layer is ready for it. */
	spin_lock(&port->port_lock);
	//将当前接收到数据req，插入到read_queue的尾部
	list_add_tail(&req->list, &port->read_queue);
	
	//唤醒gs_rx_push处理数据
	tasklet_schedule(&port->push);
	spin_unlock(&port->port_lock);
}

static void gs_write_complete(struct usb_ep *ep, struct usb_request *req)
{
	struct gs_port	*port = ep->driver_data;

	spin_lock(&port->port_lock);
	list_add(&req->list, &port->write_pool);
	port->write_started--;

	switch (req->status) {
	default:
		/* presumably a transient fault */
		pr_warn("%s: unexpected %s status %d\n",
			__func__, ep->name, req->status);
		/* FALL THROUGH */
	case 0:
		/* normal completion */
		gs_start_tx(port);
		break;

	case -ESHUTDOWN:
		/* disconnect */
		pr_vdebug("%s: %s shutdown\n", __func__, ep->name);
		break;
	}

	spin_unlock(&port->port_lock);
}