linux serial构架分析及驱动开发（1）

前面介绍了tty核心分析及tty驱动开发的方法，tty设备包括串口、终端、伪终端三大类，其中终端和伪终端驱动内核都帮我们实现好了，很少需要改动。因此我们主要介绍串口驱动的开发及其在内核中的构架（其核心实现源码主要在/drivers/serial_core.c中），这一节中我们主要分析向内核中加入一个serial驱动用到的数据结构。
serial core是构建在tty core之上的。注册一个串口驱动即在tty core层注册一个tty驱动。下面我们看看串口驱动中用到的两个最重要的数据机构 struct uart_driver 表示一个serial驱动，struct uart_port 表示一个串口端口。

struct uart_driver {

struct module *owner;

const char *driver_name; //驱动名称

const char *dev_name; //设备名基础

int major; //主设备号

int minor; //起始次设备号

int nr; //设备个数

struct console *cons; //关联的控制台

/*

* these are private; the low level driver should not

* touch these; they should be initialised to NULL

*/

struct uart_state *state; //串口驱动操作设备数组

struct tty_driver *tty_driver; //表征串口驱动的tty驱动

};

上面结构中struct uart_state *state指向驱动操作的串口设备相关数据结构，其中struct uart_port *port就是我们下面要介绍的描述串口设备的结构，struct uart_info *info 指向相关联的struct tty_struct 结构和数据发射时环形缓冲区struct circ_buf xmit，即串口打开时的描述信息。uart_info有两个成员在底层串口驱动会用到：xmit和tty。用户空间程序通过串口发送数据时，上层驱动将用户数据保存在xmit；而串口发送中断处理函数就是通过xmit获取到用户数据并将它们发送出去。串口接收中断处理函数需要通过tty将接收到的数据传递给行规则层。具体的成员分析我们在后面介绍具体的操作时再分析。

struct uart_port {

spinlock_t lock; /* port lock */ //串口端口锁

unsigned int iobase; /* in/out[bwl] */ //io端口基地址

unsigned char __iomem *membase; /* read/write[bwl] */
//io内存基地址，虚拟地址

unsigned int irq; /* irq number */ //中断号

unsigned int uartclk; /* base uart clock */
//串口时钟

unsigned int fifosize; /* tx fifo size */ //串口fifo缓冲大小

unsigned char x_char; /* xon/xoff char */
//xon/xoff字符

unsigned char regshift; /* reg offset shift */ //j寄存器移位

unsigned char iotype; /* io access style */ //io访问方式

unsigned char unused1;

#define UPIO_PORT (0) //端口

#define UPIO_HUB6 (1)

#define UPIO_MEM (2) //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; /* driver specific */
//关心的rx error status

unsigned int ignore_status_mask; /* driver specific */
//忽略的rx error status

struct uart_info *info; /* pointer to parent info */

struct uart_icount icount; /* statistics */

struct console *cons; /* struct console, if any */

#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; /* current modem ctrl settings */

unsigned int timeout; /* character-based timeout */

unsigned int type; /* port type */

const struct uart_ops *ops; //具体端口的相关操作函数

unsigned int custom_divisor;

unsigned int line; /* port index */

resource_size_t mapbase; /* for ioremap */ //io内存物理地址

struct device *dev; /* parent device */

unsigned char hub6; /* this should be in the 8250 driver */

unsigned char suspended;

unsigned char unused[2]; //允许串口收发字符标志

void *private_data; /* generic platform data pointer */

};

uart_iconut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 uart_icount {

__u32 cts;

__u32 dsr;

__u32 rng;

__u32 dcd;

__u32 rx; //接收字符数

__u32 tx; //发送字符数

__u32 frame; //错误帧计数

__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;

};

对于实现一个串口驱动，主要的工作量就是实现struct uart_ops *ops中的各个操作函数。

* 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 *); //获得串口的modem控制

void (*stop_tx)(struct uart_port *); //停止串口发送

void (*start_tx)(struct uart_port *); //使能串口发送

void (*send_xchar)(struct uart_port *, char ch); //发送xchar

void (*stop_rx)(struct uart_port *); //禁止串口接收

void (*enable_ms)(struct uart_port *); //使能modem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

void (*shutdown)(struct uart_port *); //关闭串口

void (*flush_buffer)(struct uart_port *); //刷新缓存

void (*set_termios)(struct uart_port *, struct ktermios *new,

struct ktermios *old);
//设置串口参数

void (*set_ldisc)(struct uart_port *);
//设置线路规程

void (*pm)(struct uart_port *, unsigned int state,

unsigned int oldstate); //电源管理

int (*set_wake)(struct uart_port *, unsigned int state);

/*

* Return a string describing the type of the port

*/

const char *(*type)(struct uart_port *);

/*

* Release IO and memory resources used by the port.

* This includes iounmap if necessary.

*/

void (*release_port)(struct uart_port *);

/*

* Request IO and memory resources used by the port.

* This includes iomapping the port if necessary.

*/

int (*request_port)(struct uart_port *);

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 *); //核实串口信息

int (*ioctl)(struct uart_port *, unsigned int, unsigned long);

#ifdef CONFIG_CONSOLE_POLL

void (*poll_put_char)(struct uart_port *, unsigned char);

int (*poll_get_char)(struct uart_port *);

#endif

};