linux设备模型之uart驱动架构分析.docx

1、linux设备模型之uart驱动架构分析一: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_dr

2、iver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

3、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.

4、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)stru

5、ct 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_d

6、river(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 = t

7、ty_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 stat

8、e(s).*/for (i = 0; i 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 put_tty_driver(normal);kfree(drv-state);return retval;从上面代码可以看出.uart_d

9、river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_

10、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

11、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-

12、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_

13、class(&port-lock, &port_lock_key);uart_configure_port(drv, state, port);/* Register the port whether its 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_wakeu

14、p(tty_dev) = 1;device_set_wakeup_enable(tty_dev, 0); elseprintk(KERN_ERR Cannot register tty device on line %dn,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u

15、art_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,.

16、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_

17、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:

18、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) calledn, line);/* tty-driver-num wont change, so we wont fail he

19、re with* tty-driver_data set to something non-NULL (and therefore* we wont 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 wont* be re-entered while allocating the info structure, or while we* request any

20、 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 h

21、ere, 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 mi

22、ddle 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 unti

23、l 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:r

24、eturn 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_

25、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;

26、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

27、_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_

28、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_

29、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

30、);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_unl