Linux裝置模型之tty&&uart驅動架構分析
阿新 • • 發佈：2019-01-08
五: uart_add_one_port()操作
在前面提到.在對uart裝置檔案過程中.會將操作轉換到對應的port上,這個port跟uart_driver是怎麼關聯起來的呢?這就是uart_add_ont_port()的主要工作了.
顧名思義,這個函式是在uart_driver增加一個port.程式碼如下:
int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
{
struct uart_state *state;
int ret = 0;
struct device *tty_dev;
BUG_ON(in_interrupt());
if (port->line >= drv->nr)
return -EINVAL;
state = drv->state + port->line;
mutex_lock(&port_mutex);
mutex_lock(&state->mutex);
if (state->port) {
ret = -EINVAL;
goto out;
}
state->port = port;
state->pm_state = -1;
port->cons = drv->cons;
port->info = state->info;
/*
* If this port is a console, then the spinlock is already
* initialised.
*/
if (!(uart_console(port) && (port->cons->flags & CON_ENABLED))) {
spin_lock_init(&port->lock);
lockdep_set_class(&port->lock, &port_lock_key);
}
uart_configure_port(drv, state, port);
/*
* Register the port whether it's detected or not. This allows
* setserial to be used to alter this ports parameters.
*/
tty_dev = tty_register_device(drv->tty_driver, port->line, port->dev);
if (likely(!IS_ERR(tty_dev))) {
device_can_wakeup(tty_dev) = 1;
device_set_wakeup_enable(tty_dev, 0);
} else
printk(KERN_ERR "Cannot register tty device on line %d\n",
port->line);
/*
* Ensure UPF_DEAD is not set.
*/
port->flags &= ~UPF_DEAD;
out:
mutex_unlock(&state->mutex);
mutex_unlock(&port_mutex);
return ret;
}
首先這個函式不能在中斷環境中使用. Uart_port->line就是對uart裝置檔案序號.它對應的也就是uart_driver->state陣列中的uart_port->line項.
它主要初始化對應uart_driver->state項.接著呼叫uart_configure_port()進行port的自動配置.然後註冊tty_device.如果使用者空間運行了udev或者已經配置好了hotplug.就會在/dev下自動生成裝置檔案了.
操作流程圖如下所示:
六:裝置節點的open操作
在使用者空間執行open操作的時候,就會執行uart_ops->open. Uart_ops的定義如下:
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,
};
對應open的操作介面為uart_open.程式碼如下:
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;
}
在這裡函式裡,繼續完成操作的裝置檔案所對應state初始化.現在使用者空間open這個裝置了.即要對這個檔案進行操作了.那uart_port也要開始工作了.即呼叫uart_startup()使其進入工作狀態.當然,也需要初始化uart_port所對應的環形緩衝區circ_buf.即state->info-> xmit.
特別要注意,在這裡將tty->driver_data = state;這是因為以後的操作只有port相關了,不需要去了解uart_driver的相關資訊.
跟蹤看一下里面呼叫的兩個重要的子函式. uart_get()和uart_startup().先分析uart_get().程式碼如下:
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);
}
從程式碼中可以看出.這裡注要是操作是初始化state->info.注意port->info就是state->info的一個副本.即port直接通過port->info可以找到它要操作的快取區.
uart_startup()程式碼如下:
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;
}
在這裡,注要完成對環形緩衝,即info->xmit的初始化.然後呼叫port->ops->startup( )將這個port帶入到工作狀態.其它的是一個可調引數的設定,就不詳細講解了.
七:裝置節點的write操作
Write操作對應的操作介面為uart_write( ).程式碼如下:
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;
circ = &state->info->xmit;
if (!circ->buf)
return 0;
spin_lock_irqsave(&port->lock, flags);
while (1) {
c = CIRC_SPACE_TO_END(circ->head, circ->tail, UART_XMIT_SIZE);
if (count < c)
c = count;
if (c <= 0)
break;
memcpy(circ->buf + circ->head, buf, c);
circ->head = (circ->head + c) & (UART_XMIT_SIZE - 1);
buf += c;
count -= c;
ret += c;
}
spin_unlock_irqrestore(&port->lock, flags);
uart_start(tty);
return ret;
}
Uart_start()程式碼如下:
static void uart_start(struct tty_struct *tty)
{
struct uart_state *state = tty->driver_data;
struct uart_port *port = state->port;
unsigned long flags;
spin_lock_irqsave(&port->lock, flags);
__uart_start(tty);
spin_unlock_irqrestore(&port->lock, flags);
}
static void __uart_start(struct tty_struct *tty)
{
struct uart_state *state = tty->driver_data;
struct uart_port *port = state->port;
if (!uart_circ_empty(&state->info->xmit) && state->info->xmit.buf &&
!tty->stopped && !tty->hw_stopped)
port->ops->start_tx(port);
}
顯然,對於write操作而言,它就是將資料copy到環形快取區.然後呼叫port->ops->start_tx()將資料寫到硬體暫存器.
八:Read操作
Uart的read操作同Tty的read操作相同,即都是呼叫ldsic->read()讀取read_buf中的內容.有對這部份內容不太清楚的,參閱<< linux裝置模型之tty驅動架構>>.
九:小結
本小節是分析serial驅動的基礎.在理解了tty驅動架構之後,再來理解uart驅動架構應該不是很難.隨著我們在linux裝置驅動分析的深入,越來越深刻的體會到,linux的裝置驅動架構很多都是相通的.只要深刻理解了一種驅動架構.舉一反三.也就很容易分析出其它架構的驅動了.