三、串口的打开

在用户空间执行open操作的时候,就会执行uart_ops->open. Uart_ops的定义如下:

tty_open=>init_dev=>initialize_tty_struct=>tty_ldisc_assign=>

将tty_ldisc_N_TTY复制给该dev

然后tty->driver->open(tty, filp);

tty->driver为上面uart_register_driver时注册的tty_driver驱动,它的操作方法集为uart_ops.

tty_fops.tty_open=>

tty->driver->open就是uart_ops.uart_open=>uart_startup=>

port->ops->startup(port)这里port的ops就是serial_pxa_pops;也这就是该物理uart口,struct uart_port的操作函数

serial_pxa_pops.startup就是serial_pxa_startup

static const struct tty_operations uart_ops = {

.open         = uart_open,

.close        = uart_close,

.write        = uart_write,

.put_char = uart_put_char,

.flush_chars  = uart_flush_chars,

.write_room   = uart_write_room,

.chars_in_buffer= uart_chars_in_buffer,

.flush_buffer = uart_flush_buffer,

.ioctl        = uart_ioctl,

.throttle = uart_throttle,

.unthrottle   = uart_unthrottle,

.send_xchar   = uart_send_xchar,

.set_termios  = uart_set_termios,

.stop         = uart_stop,

.start        = uart_start,

.hangup       = uart_hangup,

.break_ctl    = uart_break_ctl,

.wait_until_sent= uart_wait_until_sent,

#ifdef CONFIG_PROC_FS

.read_proc    = uart_read_proc,

#endif

.tiocmget = uart_tiocmget,

.tiocmset = uart_tiocmset,

};

对应open的操作接口为uart_open.代码如下:

static int uart_open(struct tty_struct *tty, struct file *filp)

{

struct uart_driver *drv = (struct uart_driver *)tty->driver->driver_state;

struct uart_state *state;

int retval, line = tty->index;

BUG_ON(!kernel_locked());

pr_debug("uart_open(%d) called\n", line);

/*

* tty->driver->num won't change, so we won't fail here with

* tty->driver_data set to something non-NULL (and therefore

* we won't get caught by uart_close()).

*/

retval = -ENODEV;

if (line >= tty->driver->num)

goto fail;

/*

* We take the semaphore inside uart_get to guarantee that we won't

* be re-entered while allocating the info structure, or while we

* request any IRQs that the driver may need.  This also has the nice

* side-effect that it delays the action of uart_hangup, so we can

* guarantee that info->tty will always contain something reasonable.

*/

state = uart_get(drv, line);

if (IS_ERR(state)) {

retval = PTR_ERR(state);

goto fail;

}

/*

* Once we set tty->driver_data here, we are guaranteed that

* uart_close() will decrement the driver module use count.

* Any failures from here onwards should not touch the count.

*/

tty->driver_data = state;

tty->low_latency = (state->port->flags & UPF_LOW_LATENCY) ? 1 : 0;

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;

}

在这里函数里,继续完成操作的设备文件所对应state初始化.现在用户空间open这个设备了.即要对这个文件进行操作了.那uart_port也要开始工作了.即调用uart_startup()使其进入工作状态.当然,也需要初始化uart_port所对应的环形缓冲区circ_buf.即state->info-> xmit.

特别要注意,在这里将tty->driver_data = state;这是因为以后的操作只有port相关了,不需要去了解uart_driver的相关信息.

跟踪看一下里面调用的两个重要的子函数. uart_get()和uart_startup().先分析uart_get().代码如下:

static struct uart_state *uart_get(struct uart_driver *drv, int line)

{

struct uart_state *state;

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);

}

//从代码中可以看出.这里注要是操作是初始化state->info.注意port->info就是state->info的一个副本.即port直接通过port->info可以找到它要操作的缓存区.

//uart_startup()代码如下:

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

{

struct uart_port *uport = state->uart_port;

struct tty_port *port = &state->port;

unsigned long page;

int retval = 0;

if (port->flags & ASYNC_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, &tty->flags);

if (uport->type == PORT_UNKNOWN)

return 0;

/*

* Initialise and allocate the transmit and temporary

* buffer.

*/

if (!state->xmit.buf) {

/* This is protected by the per port mutex */

page = get_zeroed_page(GFP_KERNEL);

if (!page)

return -ENOMEM;

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

uart_circ_clear(&state->xmit);

}

//在这里,注要完成对环形缓冲,即info->xmit的初始化.然后调用port->ops->startup( )将这个port带入到工作状态.

retval = uport->ops->startup(uport);//调用8250.c中的serial8250_startup()函数

if (retval == 0) {

if (init_hw) {

/*

* Initialise the hardware port settings.

*/

uart_change_speed(tty, state, NULL);

/*

* Setup the RTS and DTR signals once the

* port is open and ready to respond.

*/

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

uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR);

}

if (port->flags & ASYNC_CTS_FLOW) {

spin_lock_irq(&uport->lock);

if (!(uport->ops->get_mctrl(uport) & TIOCM_CTS))

tty->hw_stopped = 1;

spin_unlock_irq(&uport->lock);

}

set_bit(ASYNCB_INITIALIZED, &port->flags);

clear_bit(TTY_IO_ERROR, &tty->flags);

}

if (retval && capable(CAP_SYS_ADMIN))

retval = 0;

return retval;

}

static int serial8250_startup(struct uart_port *port)

{

struct uart_8250_port *up = (struct uart_8250_port *)port;

unsigned long flags;

unsigned char lsr, iir;

int retval;

//从结构体uart_config中取得相应的配置

up->capabilities = uart_config[up->port.type].flags;

up->mcr = 0;

if (up->port.type == PORT_16C950) {  //这里我们没有调用

……………………

}

#ifdef CONFIG_SERIAL_8250_RSA

enable_rsa(up);

#endif

//清楚FIFO  buffers并 disable 他们，但会在以后set_termios()函数中，重新使能他们

serial8250_clear_fifos(up);

//复位LSR,RX,IIR,MSR寄存器

(void) serial_inp(up, UART_LSR);

(void) serial_inp(up, UART_RX);

(void) serial_inp(up, UART_IIR);

(void) serial_inp(up, UART_MSR);

//若LSR寄存器中的值为0xFF.异常

if (!(up->port.flags & UPF_BUGGY_UART) &&(serial_inp(up, UART_LSR) == 0xff)) {

printk("ttyS%d: LSR safety check engaged!\n", up->port.line);

return -ENODEV;

}

//16850系列芯片的处理,忽略

if (up->port.type == PORT_16850) {

………………………………………………

}

if (is_real_interrupt(up->port.irq)) {

/*

* Test for UARTs that do not reassert THRE when the

* transmitter is idle and the interrupt has already

* been cleared.  Real 16550s should always reassert

* this interrupt whenever the transmitter is idle and

* the interrupt is enabled.  Delays are necessary to

* allow register changes to become visible.

*/

spin_lock_irqsave(&up->port.lock, flags);

wait_for_xmitr(up, UART_LSR_THRE);

serial_out_sync(up, UART_IER, UART_IER_THRI);

udelay(1); /* allow THRE to set */

serial_in(up, UART_IIR);

serial_out(up, UART_IER, 0);

serial_out_sync(up, UART_IER, UART_IER_THRI);

udelay(1); /* allow a working UART time to re-assert THRE */

iir = serial_in(up, UART_IIR);

serial_out(up, UART_IER, 0);

spin_unlock_irqrestore(&up->port.lock, flags);

/*

* If the interrupt is not reasserted, setup a timer to

* kick the UART on a regular basis.

*/

if (iir & UART_IIR_NO_INT) {

pr_debug("ttyS%d - using backup timer\n", port->line);

up->timer.function = serial8250_backup_timeout;

up->timer.data = (unsigned long)up;

mod_timer(&up->timer, jiffies +poll_timeout(up->port.timeout) + HZ/5);

}

}

//如果中断号有效,还要进一步判断这个中断号是否有效.具体操作为,先等待8250发送寄存器空.然后允许发送中断空的中断.然后判断IIR寄存器是否收到中断.

//如果有没有收到中断,则说明这根中断线无效.只能采用轮询的方式.关于轮询方式,我们在之后再以独立章节的形式给出分析

if (!is_real_interrupt(up->port.irq)) {

up->timer.data = (unsigned long)up;

mod_timer(&up->timer, jiffies + poll_timeout(up->port.timeout));

} else {

retval = serial_link_irq_chain(up);//定义串口的中断函数

if (retval)

return retval;

}

//如果没有设置中断号,则采用轮询方式；如果中断后有效.流程转入serial_link_irq_chain().在这个里面.会注册中断处理函数

serial_outp(up, UART_LCR, UART_LCR_WLEN8);  //ULCR.WLS=11,即选择8位

spin_lock_irqsave(&up->port.lock, flags);

if (up->port.flags & UPF_FOURPORT) {

if (!is_real_interrupt(up->port.irq))

up->port.mctrl |= TIOCM_OUT1;

}

else

{

//Most PC uarts need OUT2 raised to enable interrupts.

if (is_real_interrupt(up->port.irq))

up->port.mctrl |= TIOCM_OUT2;

}

serial8250_set_mctrl(&up->port, up->port.mctrl);

/*

* Do a quick test to see if we receive an

* interrupt when we enable the TX irq.

*/

serial_outp(up, UART_IER, UART_IER_THRI);

lsr = serial_in(up, UART_LSR);

iir = serial_in(up, UART_IIR);

serial_outp(up, UART_IER, 0);

if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT) {

if (!(up->bugs & UART_BUG_TXEN)) {

up->bugs |= UART_BUG_TXEN;

pr_debug("ttyS%d - enabling bad tx status workarounds\n",port->line);

}

} else {

up->bugs &= ~UART_BUG_TXEN;

}

spin_unlock_irqrestore(&up->port.lock, flags);

/*

* Finally, enable interrupts.  Note: Modem status interrupts

* are set via set_termios(), which will be occurring imminently

* anyway, so we don't enable them here.

*/

up->ier = UART_IER_RLSI | UART_IER_RDI;

serial_outp(up, UART_IER, up->ier);

if (up->port.flags & UPF_FOURPORT) {

unsigned int icp;

//Enable interrupts on the AST Fourport board

icp = (up->port.iobase & 0xfe0) | 0x01f;

outb_p(0x80, icp);

(void) inb_p(icp);

}

/*

* And clear the interrupt registers again for luck.

*/

(void) serial_inp(up, UART_LSR);

(void) serial_inp(up, UART_RX);

(void) serial_inp(up, UART_IIR);

(void) serial_inp(up, UART_MSR);

return 0;

}

四、串口的读

tty_driver中并末提供read接口.上层的read操作是直接到ldsic的缓存区中读数据的.那ldsic的数据是怎么送入进去的呢?继续看中断处理中的数据接收流程.即为: receive_chars().代码片段如下:

//这个应该是UART接受数据的函数uart_port结构定义在serial——core.h中

//port中断函数serial8250_handle_port()调用这个函数：

static void receive_chars(struct uart_8250_port *up, unsigned int *status)

{

……

……

uart_insert_char(&up->port, lsr, UART_LSR_OE, ch, flag);

}

//最后流据会转入uart_inset_char().这个函数是uart层提供的一个接口,代码如下:

static inline void uart_insert_char(struct uart_port *port, unsigned int status,unsigned int overrun, unsigned int ch, unsigned int flag)

{

struct tty_struct *tty = port->info->tty;

if ((status & port->ignore_status_mask & ~overrun) == 0)

tty_insert_flip_char(tty, ch, flag);

/*

* Overrun is special.  Since it's reported immediately,

* it doesn't affect the current character.

*/

if (status & ~port->ignore_status_mask & overrun)

tty_insert_flip_char(tty, 0, TTY_OVERRUN);

}

//tty_insert_filp()函数数据就直接交给了ldisc.

读数据时，read()--->调用tty_io.c中的tty_read()--->n_tty.c中的 n_tty_read(),n_tty_read()从ldisc中读取数据。

五、串口的写

static const struct file_operations tty_fops = {

.llseek  = no_llseek,

.read  = tty_read,

.write  = tty_write,

.poll  = tty_poll,

.unlocked_ioctl = tty_ioctl,

.compat_ioctl = tty_compat_ioctl,

.open  = tty_open,

.release = tty_release,

.fasync  = tty_fasync,

};

写数据时，write()--->调用tty_io.c中的 tty_write()--->调用n_tty.c中的 n_tty_write()--->调用serial_core.c中 uart_write()--->调用serial_core.c中 uart_start()--->__uart_start()--->

调用serial_core.c中 uart_send_xchar()--->调用8250.c中的写出函数serial8250_start_tx()--->调用8250.c中的transmit_chars()--->调用8250.c中的serial_outp()--->调用8250.c中的mem_serial_out()写出去