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);}
