串口驱动程序层次结构

下层为串口驱动层，它直接与硬件相接触，需要填充一个 struct uart_ops 的结构体。上层为tty层，包括tty核心层及线路规程，它们各自都有一个 ops 结构体，用户空间可以通过tty注册的字符设备节点来访问串口设备。涉及到了4个 ops 结构体，层层进行跳转。

uart_driver包含了串口设备名、串口驱动名、主次设备号、串口控制台(可选)等信息

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struct uart_driver
{
   struct module  *owner; //拥有该uart_driver的模块,一般为THIS_MODULE 
   constchar *driver_name; // 串口驱动名，串口设备文件名以驱动名为基础 
   constchar *dev_name; // 串口设备名 
   int major; //主设备号 
   int minor; //次设备号 
   int nr; // 该uart_driver支持的串口个数(最大) 
   struct console  *cons;// 其对应的console.若该uart_driver支持serial console,否则为NULL 
    .............................
   struct uart_state  *state;
   struct tty_driver  *tty_driver;   //uart_driver封装了tty_driver，使底层uart驱动不用关心ttr_driver。
};

(1)一个tty驱动程序必须注册/注销tty_driver。

(2)一个uart驱动则变为注册/注销uart_driver。

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int uart_register_driver(struct uart_driver *drv);
void uart_unregister_driver(struct uart_driver *drv);
int tty_register_driver(struct tty_driver *drv);
void tty_unregister_driver(struct tty_driver *drv);

uart_port用于描述一个UART端口（直接对应于一个串口）的I/O端口或I/O内存地址、FIFO大小、端口类型等信息。

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struct uart_port {
	spinlock_t lock;/* 串口端口锁 */
	unsignedint iobase;/* IO端口基地址 */
	unsignedchar __iomem *membase;/* IO内存基地址,经映射(如ioremap)后的IO内存虚拟基地址 */
	unsignedint irq;/* 中断号 */
	unsignedint uartclk;/* 串口时钟 */
	unsignedint fifosize;/* 串口FIFO缓冲大小 */
	unsignedchar x_char;/* xon/xoff字符 */
	unsignedchar regshift;/* 寄存器位移 */
	unsignedchar iotype;/* IO访问方式 */
	unsignedchar unused1;

	#define UPIO_PORT (0)/* IO端口 */
	#define UPIO_HUB6 (1)
	#define UPIO_MEM (2)/* IO内存 */
	#define UPIO_MEM32 (3)
	#define UPIO_AU (4)/* Au1x00 type IO */
	#define UPIO_TSI (5)/* Tsi108/109 type IO */
	#define UPIO_DWAPB (6)/* DesignWare APB UART */
	#define UPIO_RM9000 (7)/* RM9000 type IO */

	unsignedint read_status_mask;/* 关心的Rx error status */
	unsignedint ignore_status_mask;/* 忽略的Rx error status */
	struct uart_info *info;        //重要，见下面
	struct uart_icount  icount;   /* 计数器 uart_icount为串口信息计数器，包含了发送字符计数、接收字符计数等。在串口的发送中断处理函数和接收中断处理函数中，我们需要管理这些计数。*/ 

	struct console *cons;/* console结构体 */
	#ifdefCONFIG_SERIAL_CORE_CONSOLE
	unsignedlong sysrq;/* sysrq timeout */
	#endif

	upf_t flags;

	#define UPF_FOURPORT ((__forceupf_t)(1 << 1))
    #define UPF_SAK ((__forceupf_t)(1 << 2))
    #define UPF_SPD_MASK ((__forceupf_t)(0x1030))
    #define UPF_SPD_HI ((__forceupf_t)(0x0010))
    #define UPF_SPD_VHI ((__forceupf_t)(0x0020))
    #define UPF_SPD_CUST ((__forceupf_t)(0x0030))
    #define UPF_SPD_SHI ((__forceupf_t)(0x1000))
    #define UPF_SPD_WARP ((__forceupf_t)(0x1010))
    #define UPF_SKIP_TEST ((__forceupf_t)(1 << 6))
    #define UPF_AUTO_IRQ ((__forceupf_t)(1 << 7))
    #define UPF_HARDPPS_CD ((__forceupf_t)(1 << 11))
    #define UPF_LOW_LATENCY ((__forceupf_t)(1 << 13))
    #define UPF_BUGGY_UART ((__forceupf_t)(1 << 14))
    #define UPF_MAGIC_MULTIPLIER((__force upf_t)(1 << 16))
    #define UPF_CONS_FLOW ((__forceupf_t)(1 << 23))
    #define UPF_SHARE_IRQ ((__forceupf_t)(1 << 24))
    #define UPF_BOOT_AUTOCONF ((__forceupf_t)(1 << 28))
    #define UPF_FIXED_PORT ((__forceupf_t)(1 << 29))
    #define UPF_DEAD ((__forceupf_t)(1 << 30))
    #define UPF_IOREMAP ((__forceupf_t)(1 << 31))

    #define UPF_CHANGE_MASK ((__forceupf_t)(0x17fff))
    #define UPF_USR_MASK ((__forceupf_t)(UPF_SPD_MASK|UPF_LOW_LATENCY))

    unsigned int mctrl;/* 当前的moden设置 */
    unsigned int timeout;/* character-based timeout */
    unsigned int type;/* 端口类型 */
    const struct uart_ops *ops;/* 串口端口操作函数集 */
    unsigned int custom_divisor;
    unsigned int  line;/* 端口索引 */
    resource_size_t mapbase;/* IO内存物理基地址，可用于ioremap */
    struct device *dev;/* 父设备 */
    unsigned char hub6;/* this should be in the 8250 driver */
    unsigned char suspended;
    unsigned char unused[2];
    void*private_data;/* 端口私有数据,一般为platform数据指针 */
};