struct uart_driver {
    struct module     *owner;           // 拥有该uart_driver的模块,一般为THIS_MODULE */
    const char        *driver_name;     // 串口驱动名，串口设备文件名以驱动名为基础 */
    const char        *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 */

     // these are private; the low level driver should not
     // touch these; they should be initialised to NULL
    struct uart_state *state;
    struct tty_driver *tty_driver;
};

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

    unsigned int        read_status_mask;  // 关心的Rx error status */
    unsigned int        ignore_status_mask;// 忽略的Rx error status */
    struct uart_info      *info;           // pointer to parent info */
    struct uart_icount     icount;         // 计数器 */

    struct console        *cons;           // console结构体 */
#ifdef CONFIG_SERIAL_CORE_CONSOLE
    unsigned long         sysrq;           // sysrq timeout */
#endif

    upf_t                 flags;

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

#define UPF_CHANGE_MASK      ((__force upf_t) (0x17fff))
#define UPF_USR_MASK         ((__force upf_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 */
};

struct uart_icount {
    __u32    cts;
    __u32    dsr;
    __u32    rng;
    __u32    dcd;
    __u32    rx;      // 发送字符计数 */
    __u32    tx;      // 接受字符计数 */
    __u32    frame;   // 帧错误计数 */
    __u32    overrun; // Rx FIFO溢出计数 */
    __u32    parity;  // 帧校验错误计数 */
    __u32    brk;     // break计数 */
    __u32    buf_overrun;
};

// uart_info实例仅在串口端口打开时有效，它可能在串口关闭时被串口核心层释放。因此，在使用uart_port的uart_info成员时必须保证串口已打开。底层驱动和核心层驱动都可以修改uart_info实例。
 // This is the state information which is only valid when the port
 // is open; it may be freed by the core driver once the device has
 // been closed. Either the low level driver or the core can modify
 // stuff here.
struct uart_info {
    struct tty_struct     *tty;
    struct circ_buf        xmit;
    uif_t                  flags;

 // Definitions for info->flags. These are _private_ to serial_core, and
 // are specific to this structure. They may be queried by low level drivers.
#define UIF_CHECK_CD        ((__force uif_t) (1 << 25))
#define UIF_CTS_FLOW        ((__force uif_t) (1 << 26))
#define UIF_NORMAL_ACTIVE    ((__force uif_t) (1 << 29))
#define UIF_INITIALIZED        ((__force uif_t) (1 << 31))
#define UIF_SUSPENDED        ((__force uif_t) (1 << 30))

    int                     blocked_open;

    struct tasklet_struct   tlet;

    wait_queue_head_t       open_wait;
    wait_queue_head_t       delta_msr_wait;
};

// This structure describes all the operations that can be
// done on the physical hardware.
struct uart_ops {
    unsigned int (*tx_empty)(struct uart_port *); // 串口的Tx FIFO缓存是否为空 */
    void         (*set_mctrl)(struct uart_port *, unsigned int mctrl); // 设置串口modem控制 */
    unsigned int (*get_mctrl)(struct uart_port *); // 获取串口modem控制 */
    void         (*stop_tx)(struct uart_port *); // 禁止串口发送数据 */
    void         (*start_tx)(struct uart_port *); // 使能串口发送数据 */
    void         (*send_xchar)(struct uart_port *, char ch);// 发送xChar */
    void         (*stop_rx)(struct uart_port *); // 禁止串口接收数据 */
    void         (*enable_ms)(struct uart_port *); // 使能modem的状态信号 */
    void         (*break_ctl)(struct uart_port *, int ctl); // 设置break信号 */
    int          (*startup)(struct uart_port *); // 启动串口,应用程序打开串口设备文件时,该函数会被调用 */
    void         (*shutdown)(struct uart_port *); // 关闭串口,应用程序关闭串口设备文件时,该函数会被调用 */
    void         (*set_termios)(struct uart_port *, struct ktermios *new, struct ktermios *old); //设置串口参数 */
    void         (*pm)(struct uart_port *, unsigned int state,
             unsigned int oldstate); // 串口电源管理 */
    int          (*set_wake)(struct uart_port *, unsigned int state); 
    const char  *(*type)(struct uart_port *); // 返回一描述串口类型的字符串 */
    void         (*release_port)(struct uart_port *); // 释放串口已申请的IO端口/IO内存资源,必要时还需iounmap */
    int          (*request_port)(struct uart_port *); //申请必要的IO端口/IO内存资源,必要时还可以重新映射串口端口 */
    void         (*config_port)(struct uart_port *, int); // 执行串口所需的自动配置 */
    int          (*verify_port)(struct uart_port *, struct serial_struct *); // 核实新串口的信息 */
    int          (*ioctl)(struct uart_port *, unsigned int, unsigned long); // IO控制 */
};