Linux TTY驱动--Serial Core层-优快云博客

接上一节：

Linux TTY驱动--Uart_driver底层

一. 为了给USB-Serial类型的串口打基础（USB-Serial和Serial Core一样，构造了一个tty_driver和tty_operations,叫做usb-serial层），这里仔细分析Serial Core层完成的工作，实现代码为/drivers/serial/serial_core.c(kernel 2.6.28)。从哪里讲起呢，还是找找module_init，发现没有，在/drivers/serial/*众多文件里寻找没有，怀疑Serial Core层不是一个驱动模块，只能导出了一些上篇文章的函数而已。那就只有从uart_register_driver函数开始了，不过首先看看serial_core.c文件中使用的结构体或者常量，发现了如下：

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,
   .set_ldisc   = uart_set_ldisc,
   .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,
#ifdef CONFIG_CONSOLE_POLL
   .poll_init   = uart_poll_init,
   .poll_get_char   = uart_poll_get_char,
   .poll_put_char   = uart_poll_put_char,
#endif
};

该结构体非常重要，是Core层和TTY层沟通的接口。在uart_register_driver的过程为：

1. 调用alloc_tty_driver（tty层函数）初始化一个tty_driver

2. 调用tty_set_operations(tty层) 给tty_driver 赋值上面的 uart_ops

3. 通过tty_register_driver向tty层注册tty_driver（/drivers/char/tty_io.c中实现kernel2.6.28）。以上的uart_ops被tty层在需要时调用。

二. 那么重点看一下 tty_driver、tty_operations两个结构体

struct tty_driver {
   int   magic;       /* magic number for this structure */
   struct kref kref;   /* Reference management */
   struct cdev cdev;
   struct module   *owner;
   const char   *driver_name;
   const char   *name;
   int   name_base;   /* offset of printed name */
   int   major;       /* major device number */
   int   minor_start;   /* start of minor device number */
   int   minor_num;   /* number of *possible* devices */
   int   num;       /* number of devices allocated */
   short   type;       /* type of tty driver */
   short   subtype;   /* subtype of tty driv