linux serial构架分析及驱动开发（5）

//原文地址：http://blog.csdn.net/sirzjp/article/details/6170596

uart_close主要在tty_release和do_tty_hundup中调用，做与uart_pen相反的操作，具体源码如下：

/*

 * In 2.4.5, calls to this will be serialized via the BKL in

 *  linux/drivers/char/tty_io.c:tty_release()

 *  linux/drivers/char/tty_io.c:do_tty_handup()

 */

static void uart_close(struct tty_struct *tty, struct file *filp)

{

 struct uart_state *state = tty->driver_data; //uart_open中我们做的赋值
 struct uart_port *port;

 BUG_ON(!kernel_locked());

 if (!state || !state->port)

  return;

 port = state->port;

 pr_debug("uart_close(%d) called/n", port->line);

 mutex_lock(&state->mutex);

 if (tty_hung_up_p(filp))

  goto done;

 if ((tty->count == 1) && (state->count != 1)) {

  /*

   * Uh, oh.  tty->count is 1, which means that the tty

   * structure will be freed.  state->count should always

   * be one in these conditions.  If it's greater than

   * one, we've got real problems, since it means the

   * serial port won't be shutdown.

   */

  printk(KERN_ERR "uart_close: bad serial port count; tty->count is 1, "

         "state->count is %d/n", state->count);

  state->count = 1;

 }

 if (--state->count < 0) {

  printk(KERN_ERR "uart_close: bad serial port count for %s: %d/n",

         tty->name, state->count);

  state->count = 0;

 }

//只有state->count 为0才说明此外没有对串口的操作可以关闭串口
 if (state->count)

  goto done;

 /*

  * Now we wait for the transmit buffer to clear; and we notify

  * the line discipline to only process XON/XOFF characters by

  * setting tty->closing.

  */

 tty->closing = 1;

 

//在关闭之前先把缓存中或者待发送的数据先发送完，这里先唤醒写等待队列，然后调用wait_until_sent发送数据

//该函数主要将数据发射出去

 if (state->closing_wait != USF_CLOSING_WAIT_NONE)

  tty_wait_until_sent(tty, msecs_to_jiffies(state->closing_wait));

 /*

  * At this point, we stop accepting input.  To do this, we

  * disable the receive line status interrupts.

  */

 if (state->info.flags & UIF_INITIALIZED) {

  unsigned long flags;

  spin_lock_irqsave(&port->lock, flags);

  port->ops->stop_rx(port);   //停止发送数据
  spin_unlock_irqrestore(&port->lock, flags);

  /*

   * Before we drop DTR, make sure the UART transmitter

   * has completely drained; this is especially

   * important if there is a transmit FIFO!

   */

  uart_wait_until_sent(tty, port->timeout);

 }

//清除一些标志，释放串口资源

 uart_shutdown(state);

//对发送缓存及其标志做清理
 uart_flush_buffer(tty);

//对线路规程中的数据做清理

 tty_ldisc_flush(tty);

 tty->closing = 0;

 state->info.port.tty = NULL;

//若有其他进程在等待打开次串口，先等待一段时间，然后清理打开标志，并在最后唤醒等待的进程

 if (state->info.port.blocked_open) {

  if (state->close_delay)

   msleep_interruptible(state->close_delay);

 } else if (!uart_console(port)) {

  uart_change_pm(state, 3);

 }

 /*

  * Wake up anyone trying to open this port.

  */

 state->info.flags &= ~UIF_NORMAL_ACTIVE;

 wake_up_interruptible(&state->info.port.open_wait);

 done:

 mutex_unlock(&state->mutex);

}