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分类: LINUX

2008-08-06 17:12:22

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一:前言
接着前面的终端控制台分析,接下来分析serial的驱动.在linux中,serial也对应着终端,通常被称为串口终端.在shell上,我们看到的/dev/ttyS*就是串口终端所对应的设备节点.
在分析具体的serial驱动之前.有必要先分析uart驱动架构.uart是Universal Asynchronous Receiver and Transmitter的缩写.翻译成中文即为”通用异步收发器”.它是串口设备驱动的封装层.
二:uart驱动架构概貌
如下图所示:
 
 
上图中红色部份标识即为uart部份的操作.
从上图可以看到,uart设备是继tty_driver的又一层封装.实际上uart_driver就是对应tty_driver.在它的操作函数中,将操作转入uart_port.
在写操作的时候,先将数据放入一个叫做circ_buf的环形缓存区.然后uart_port从缓存区中取数据,将其写入到串口设备中.
当uart_port从serial设备接收到数据时,会将设备放入对应line discipline的缓存区中.
这样.用户在编写串口驱动的时候,只先要注册一个uart_driver.它的主要作用是定义设备节点号.然后将对设备的各项操作封装在uart_port.驱动工程师没必要关心上层的流程,只需按硬件规范将uart_port中的接口函数完成就可以了.
 
三:uart驱动中重要的数据结构及其关联
我们可以自己考虑下,基于上面的架构代码应该要怎么写.首先考虑以下几点:
1: 一个uart_driver通常会注册一段设备号.即在用户空间会看到uart_driver对应有多个设备节点.例如:
/dev/ttyS0  /dev/ttyS1
每个设备节点是对应一个具体硬件的,从上面的架构来看,每个设备文件应该对应一个uart_port.
也就是说:uart_device怎么同多个uart_port关系起来?怎么去区分操作的是哪一个设备文件?
 
2:每个uart_port对应一个circ_buf,所以uart_port必须要和这个缓存区关系起来
 
回忆tty驱动架构中.tty_driver有一个叫成员指向一个数组,即tty->ttys.每个设备文件对应设数组中的一项.而这个数组所代码的数据结构为tty_struct. 相应的tty_struct会将tty_driver和ldisc关联起来.
那在uart驱动中,是否也可用相同的方式来处理呢?
将uart驱动常用的数据结构表示如下:
 
 
结合上面提出的疑问.可以很清楚的看懂这些结构的设计.
 
四:uart_driver的注册操作
Uart_driver注册对应的函数为: uart_register_driver()代码如下:
int uart_register_driver(struct uart_driver *drv)
{
     struct tty_driver *normal = NULL;
     int i, retval;
 
     BUG_ON(drv->state);
 
     /*
      * Maybe we should be using a slab cache for this, especially if
      * we have a large number of ports to handle.
      */
     drv->state = kzalloc(sizeof(struct uart_state) * drv->nr, GFP_KERNEL);
     retval = -ENOMEM;
     if (!drv->state)
         goto out;
 
     normal  = alloc_tty_driver(drv->nr);
     if (!normal)
         goto out;
 
     drv->tty_driver = normal;
 
     normal->owner      = drv->owner;
     normal->driver_name    = drv->driver_name;
     normal->name       = drv->dev_name;
     normal->major      = drv->major;
     normal->minor_start    = drv->minor;
     normal->type       = TTY_DRIVER_TYPE_SERIAL;
     normal->subtype        = SERIAL_TYPE_NORMAL;
     normal->init_termios   = tty_std_termios;
     normal->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
     normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 9600;
     normal->flags      = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
     normal->driver_state    = drv;
     tty_set_operations(normal, &uart_ops);
 
     /*
      * Initialise the UART state(s).
      */
     for (i = 0; i < drv->nr; i++) {
         struct uart_state *state = drv->state + i;
 
         state->close_delay     = 500;    /* .5 seconds */
         state->closing_wait    = 30000;  /* 30 seconds */
 
         mutex_init(&state->mutex);
     }
 
     retval = tty_register_driver(normal);
 out:
     if (retval < 0) {
         put_tty_driver(normal);
         kfree(drv->state);
     }
     return retval;
}
从上面代码可以看出.uart_driver中很多数据结构其实就是tty_driver中的.将数据转换为tty_driver之后,注册tty_driver.然后初始化uart_driver->state的存储空间.
这样,就会注册uart_driver->nr个设备节点.主设备号为uart_driver-> major. 开始的次设备号为uart_driver-> minor.
值得注意的是.在这里将tty_driver的操作集统一设为了uart_ops.其次,在tty_driver-> driver_state保存了这个uart_driver.这样做是为了在用户空间对设备文件的操作时,很容易转到对应的uart_driver.
另外:tty_driver的flags成员值为: TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV.里面包含有TTY_DRIVER_DYNAMIC_DEV标志.结合之前对tty的分析.如果包含有这个标志,是不会在初始化的时候去注册device.也就是说在/dev/下没有动态生成结点(如果是/dev下静态创建了这个结点就另当别论了^_^).
 
流程图如下:
 
 
五: uart_add_one_port()操作
在前面提到.在对uart设备文件过程中.会将操作转换到对应的port上,这个port跟uart_driver是怎么关联起来的呢?这就是uart_add_ont_port()的主要工作了.
顾名思义,这个函数是在uart_driver增加一个port.代码如下:
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;
}
首先这个函数不能在中断环境中使用. Uart_port->line就是对uart设备文件序号.它对应的也就是uart_driver->state数组中的uart_port->line项.
它主要初始化对应uart_driver->state项.接着调用uart_configure_port()进行port的自动配置.然后注册tty_device.如果用户空间运行了udev或者已经配置好了hotplug.就会在/dev下自动生成设备文件了.
操作流程图如下所示:
 
 
六:设备节点的open操作
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:
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 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.其它的是一个可调参数的设置,就不详细讲解了.
 
七:设备节点的write操作
Write操作对应的操作接口为uart_write( ).代码如下:
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()代码如下:
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);
}
 
显然,对于write操作而言,它就是将数据copy到环形缓存区.然后调用port->ops->start_tx()将数据写到硬件寄存器.
 
八:Read操作
Uart的read操作同Tty的read操作相同,即都是调用ldsic->read()读取read_buf中的内容.有对这部份内容不太清楚的,参阅<< linux设备模型之tty驱动架构>>.
 
九:小结
本小节是分析serial驱动的基础.在理解了tty驱动架构之后,再来理解uart驱动架构应该不是很难.随着我们在linux设备驱动分析的深入,越来越深刻的体会到,linux的设备驱动架构很多都是相通的.只要深刻理解了一种驱动架构.举一反三.也就很容易分析出其它架构的驱动了.
 
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给主人留下些什么吧!~~

chinaunix网友2010-07-23 09:32:11

楼主是人才啊,坚持下去必有回报。我也准备建一个博客,很多笔记看过之后1/2年没用也就忘了,而且如果要写出来的话,必然要求自己是真的懂了,所以建个博客分享笔记是不错的

chinaunix网友2010-07-23 09:32:11

楼主是人才啊,坚持下去必有回报。我也准备建一个博客,很多笔记看过之后1/2年没用也就忘了,而且如果要写出来的话,必然要求自己是真的懂了,所以建个博客分享笔记是不错的

chinaunix网友2010-07-23 09:32:11

楼主是人才啊,坚持下去必有回报。我也准备建一个博客,很多笔记看过之后1/2年没用也就忘了,而且如果要写出来的话,必然要求自己是真的懂了,所以建个博客分享笔记是不错的

chinaunix网友2010-06-29 16:01:35

分析的挺不错,佩服。

chinaunix网友2010-06-29 16:01:35

分析的挺不错,佩服。