tty->alt_speed = 0;

state->info->tty = tty;

/*

* If the port is in the middle of closing, bail out now.

*/

if (tty_hung_up_p(filp)) {

retval = -EAGAIN;

state->count--;

mutex_unlock(state->mutex);

goto fail;

}

/*

* Make sure the device is in D0 state.

*/

if (state->count == 1)

uart_change_pm(state, 0);

/*

* Start up the serial port.

*/

retval = uart_startup(state, 0);

/*

* If we succeeded, wait until the port is ready.

*/

if (retval == 0)

retval = uart_block_til_ready(filp, state);

mutex_unlock(state->mutex);

/*

* If this is the first open to succeed, adjust things to suit.

*/

if (retval == 0 !(state->info->flags UIF_NORMAL_ACTIVE)) {

state->info->flags |= UIF_NORMAL_ACTIVE;

uart_update_termios(state);

}

fail:

return retval;

}

int ret = 0;

state = drv->state + line;

if (mutex_lock_interruptible(state->mutex)) {

ret = -ERESTARTSYS;

goto err;

}

state->count++;

if (!state->port || state->port->flags UPF_DEAD) {

ret = -ENXIO;

goto err_unlock;

}

if (!state->info) {

state->info = kzalloc(sizeof(struct uart_info)， GFP_KERNEL);

if (state->info) {

init_waitqueue_head(state->info->open_wait);

init_waitqueue_head(state->info->delta_msr_wait);

/*

* Link the info into the other structures.

*/

state->port->info = state->info;

tasklet_init(state->info->tlet, uart_tasklet_action,

(unsigned long)state);

} else {

ret = -ENOMEM;

goto err_unlock;

}

}

return state;

err_unlock:

state->count--;

mutex_unlock(state->mutex);

err:

return ERR_PTR(ret);

}

從代碼中可以看出。這里注要是操作是初始化state->info.注意port->info就是state->info的一個(gè)副本。即port直接通過(guò)port->info可以找到它要操作的緩存區(qū)。

uart_startup()代碼如下：

static int uart_startup(struct uart_state *state, int init_hw)

{

struct uart_info *info = state->info;

struct uart_port *port = state->port;

unsigned long page;

int retval = 0;

if (info->flags UIF_INITIALIZED)

return 0;

/*

* Set the TTY IO error marker - we will only clear this

* once we have successfully opened the port. Also set

* up the tty->alt_speed kludge

*/

set_bit(TTY_IO_ERROR, info->tty->flags);

if (port->type == PORT_UNKNOWN)

return 0;

/*

* Initialise and allocate the transmit and temporary

* buffer.

*/

if (!info->xmit.buf) {

page = get_zeroed_page(GFP_KERNEL);

if (!page)

return -ENOMEM;

info->xmit.buf = (unsigned char *) page;

uart_circ_clear(info->xmit);

}

retval = port->ops->startup(port);

if (retval == 0) {

if (init_hw) {

/*

* Initialise the hardware port settings.

*/

uart_change_speed(state, NULL);

/*

* Setup the RTS and DTR signals once the

* port is open and ready to respond.

*/

if (info->tty->termios->c_cflag CBAUD)

uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);

}

if (info->flags UIF_CTS_FLOW) {

spin_lock_irq(port->lock);

if (!(port->ops->get_mctrl(port) TIOCM_CTS))

info->tty->hw_stopped = 1;

spin_unlock_irq(port->lock);

}

info->flags |= UIF_INITIALIZED;

clear_bit(TTY_IO_ERROR, info->tty->flags);

}

if (retval capable(CAP_SYS_ADMIN))

retval = 0;

return retval;

}

在這里，注要完成對(duì)環(huán)形緩沖，即info->xmit的初始化。然后調(diào)用port->ops->startup( )將這個(gè)port帶入到工作狀態(tài)。其它的是一個(gè)可調(diào)參數(shù)的設(shè)置，就不詳細(xì)講解了。

七：設(shè)備節(jié)點(diǎn)的write操作

Write操作對(duì)應(yīng)的操作接口為uart_write( )。代碼如下：

static int

uart_write(struct tty_struct *tty, const unsigned char *buf, int count)

{

struct uart_state *state = tty->driver_data;

struct uart_port *port;

struct circ_buf *circ;

unsigned long flags;

int c, ret = 0;

/*

* This means you called this function _after_ the port was

* closed. No cookie for you.

*/

if (!state || !state->info) {

WARN_ON(1);

return -EL3HLT;

}

port = state->port;