二十六【uart】Uart驱动架构分析

一、前言

　　在linux中，serial也对应着终端你，通常被称为串口终端。在shell上，我们看到得/dev/ttyS*就是串口终端所对应的设备节点。

　　uart(Universal Asynchronous Receicer and transmitter)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

 

 　　从上图可以看到，uart设备是继tty_drivers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驱动代码分析

1、uart驱动注册函数

drivers/tty/serial/serial_core.c

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/**  *  uart_register_driver - register a driver with the uart core layer  *  @drv: low level driver structure  *  *  Register a uart driver with the core driver.  We in turn register  *  with the tty layer, and initialise the core driver per-port state.  *  *  We have a proc file in /proc/tty/driver which is named after the  *  normal driver.  *  *  drv->port should be NULL, and the per-port structures should be  *  registered using uart_add_one_port after this call has succeeded.  */ int uart_register_driver(struct uart_driver *drv) {     struct tty_driver *normal;     int i, retval = -ENOMEM;       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 = kcalloc(drv->nr, sizeof(struct uart_state), GFP_KERNEL);     if (!drv->state)         goto out;       normal = alloc_tty_driver(drv->nr);     if (!normal)         goto out_kfree;       drv->tty_driver = normal;              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 = B4000000 | CS8 | CREAD | HUPCL | CLOCAL;     normal->init_termios.c_ispeed = normal->init_termios.c_ospeed = 4000000;   //默认的波特率     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;         struct tty_port *port = &state->port;           tty_port_init(port);   //端口初始化         port->ops = &uart_port_ops;     }            //驱动注册     retval = tty_register_driver(normal);     if (retval >= 0)         return retval;       for (i = 0; i < drv->nr; i++)         tty_port_destroy(&drv->state[i].port);     put_tty_driver(normal); out_kfree:     kfree(drv->state); out:     return retval; }

2、添加端口函数uart_add_one_port（）

在uart_driver增加一个port

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/**  *  uart_add_one_port - attach a driver-defined port structure  *  @drv: pointer to the uart low level driver structure for this port  *  @uport: uart port structure to use for this port.  *  *  This allows the driver to register its own uart_port structure  *  with the core driver.  The main purpose is to allow the low  *  level uart drivers to expand uart_port, rather than having yet  *  more levels of structures.  */ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport) {     struct uart_state *state;     struct tty_port *port;     int ret = 0;     struct device *tty_dev;     int num_groups;       BUG_ON(in_interrupt());       if (uport->line >= drv->nr)         return -EINVAL;       state = drv->state + uport->line;     port = &state->port;       mutex_lock(&port_mutex);     mutex_lock(&port->mutex);     if (state->uart_port) {         ret = -EINVAL;         goto out;     }       /* Link the port to the driver state table and vice versa */     atomic_set(&state->refcount, 1);     init_waitqueue_head(&state->remove_wait);     state->uart_port = uport;     uport->state = state;       state->pm_state = UART_PM_STATE_UNDEFINED;     uport->cons = drv->cons;     uport->minor = drv->tty_driver->minor_start + uport->line;     uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name,                 drv->tty_driver->name_base + uport->line);     if (!uport->name) {         ret = -ENOMEM;         goto out;     }       /*      * If this port is a console, then the spinlock is already      * initialised.      */     if (!(uart_console(uport) && (uport->cons->flags & CON_ENABLED))) {         spin_lock_init(&uport->lock);         lockdep_set_class(&uport->lock, &port_lock_key);     }     if (uport->cons && uport->dev)         of_console_check(uport->dev->of_node, uport->cons->name, uport->line);       tty_port_link_device(port, drv->tty_driver, uport->line);     uart_configure_port(drv, state, uport);       port->console = uart_console(uport);       num_groups = 2;     if (uport->attr_group)         num_groups++;       uport->tty_groups = kcalloc(num_groups, sizeof(*uport->tty_groups),                     GFP_KERNEL);     if (!uport->tty_groups) {         ret = -ENOMEM;         goto out;     }     uport->tty_groups[0] = &tty_dev_attr_group;     if (uport->attr_group)         uport->tty_groups[1] = uport->attr_group;       /*      * Register the port whether it's detected or not.  This allows      * setserial to be used to alter this port's parameters.      */     tty_dev = tty_port_register_device_attr_serdev(port, drv->tty_driver,             uport->line, uport->dev, port, uport->tty_groups);     if (!IS_ERR(tty_dev)) {         device_set_wakeup_capable(tty_dev, 1);     } else {         dev_err(uport->dev, "Cannot register tty device on line %d\n",                uport->line);     }       /*      * Ensure UPF_DEAD is not set.      */     uport->flags &= ~UPF_DEAD;    out:     mutex_unlock(&port->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.

3、串口的文件操作集合

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static const struct tty_operations uart_ops = {     .install    = uart_install,     .open       = uart_open,     .close      = uart_close,     .write      = uart_write,     .put_char   = uart_put_char,  //单字符写入     .flush_chars    = uart_flush_chars,     .write_room = uart_write_room,     //检测缓冲区的剩余空间     .chars_in_buffer= uart_chars_in_buffer,   //检测包含数据缓冲区的数量     .flush_buffer   = uart_flush_buffer,   //刷新缓冲区并丢弃其中的数据     .ioctl      = uart_ioctl,     .throttle   = uart_throttle,     .unthrottle = uart_unthrottle,     .send_xchar = uart_send_xchar,     .set_termios    = uart_set_termios,     .set_ldisc  = uart_set_ldisc,   //设置线路规程的函数     .stop       = uart_stop,     .start      = uart_start,     .hangup     = uart_hangup,     .break_ctl  = uart_break_ctl,     .wait_until_sent= uart_wait_until_sent,  //用来向硬件发送数据 #ifdef CONFIG_PROC_FS     .proc_show  = uart_proc_show, #endif     .tiocmget   = uart_tiocmget,    //获取特定tty设备当前的线路设置     .tiocmset   = uart_tiocmset,    //设置特定tty设备当前的线路     .set_serial = uart_set_info_user,     .get_serial = uart_get_info_user,     .get_icount = uart_get_icount, #ifdef CONFIG_CONSOLE_POLL     .poll_init  = uart_poll_init,     .poll_get_char  = uart_poll_get_char,     .poll_put_char  = uart_poll_put_char, #endif };