linux 串口驱动

一.核心数据结构

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 */
};

二、串口驱动API

/* 功能： uart_register_driver用于将串口驱动uart_driver注册到内核(串口核心层)中，通常在模块初始化函数调用该函数。
* 参数 drv：要注册的uart_driver

* 返回值： 成功，返回0；否则返回错误码
*/
int uart_register_driver(struct uart_driver *drv)


 /* 功能： uart_unregister_driver用于注销我们已注册的uart_driver，通常在模块卸载函数调用该函数
* 参数 drv：要注销的uart_driver

* 返回值： 成功，返回0；否则返回错误码
*/
void uart_unregister_driver(struct uart_driver *drv)
 
 
/* 功能： uart_add_one_port用于为串口驱动添加一个串口端口，通常在探测到设备后(驱动的设备probe方法)调用该函数
* 参数 drv：串口驱动
* port:要添加的串口端口

* 返回值： 成功，返回0；否则返回错误码
*/
int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
 
 
/* 功能： uart_remove_one_port用于删除一个已添加到串口驱动中的串口端口，通常在驱动卸载时调用该函数
* 参数 drv： 串口驱动
* port: 要删除的串口端口
* 返回值： 成功，返回0；否则返回错误码
*/
int uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
 
 
/* 功能： uart_write_wakeup唤醒上层因向串口端口写数据而阻塞的进程，通常在串口发送中断处理函数中调用该函数
* 参数 port：需要唤醒写阻塞进程的串口端口
*/
void uart_write_wakeup(struct uart_port *port)
 
/* 功能： uart_suspend_port用于挂起特定的串口端口
* 参数 drv： 要挂起的串口端口所属的串口驱动
* port：要挂起的串口端口
* 返回值： 成功返回0；否则返回错误码
*/
int uart_suspend_port(struct uart_driver *drv, struct uart_port *port)
 

/* 功能： uart_resume_port用于恢复某一已挂起的串口
* 参数 drv： 要恢复的串口端口所属的串口驱动
* port：要恢复的串口端口
* 返回值： 成功返回0；否则返回错误码
*/
int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
 

/* 功能： uart_get_baud_rate通过解码termios结构体来获取指定串口的波特率
* 参数 port： 要获取波特率的串口端口
* termios：当前期望的termios配置(包含串口波特率)
* old： 以前的termios配置，可以为NULL
* min： 可接受的最小波特率
* max： 可接受的最大波特率
* 返回值： 串口的波特率
*/
unsigned int
uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,struct ktermios *old, unsigned int min, unsigned int max)
 
/* 功能： uart_get_divisor用于计算某一波特率的串口时钟分频数（串口波特率除数）
* 参数 port：要计算时钟分频数的串口端口
* baud：期望的波特率
*返回值： 串口时钟分频数
*/
unsigned int uart_get_divisor(struct uart_port *port, unsigned int baud)
 

/* 功能： uart_update_timeout用于更新（设置）串口FIFO超时时间
* 参数 port： 要更新超时时间的串口端口
* cflag：termios结构体的cflag值
* baud： 串口的波特率
*/
void uart_update_timeout(struct uart_port *port, unsigned int cflag, unsigned int baud)
 

/* 功能：uart_match_port用于判断两串口端口是否为同一端口
* 参数 port1、port2：要判断的串口端口
* 返回值：不同返回0；否则返回非0
*/
int uart_match_port(struct uart_port *port1, struct uart_port *port2)
 
/* 功能： uart_console_write用于向串口端口写一控制台信息

* 参数 port: 要写信息的串口端口
* s: 要写的信息
* count: 信息的大小
* putchar: 用于向串口端口写字符的函数，该函数函数有两个参数：串口端口和要写的字符
*/
void uart_console_write(struct uart_port *port, const char *s,unsigned int count,void (*putchar)(struct uart_port *, int))
 

三.串口驱动例子

 

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/fcntl.h> /* O_ACCMODE */
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_*_user */
#include <linux/ioctl.h>
#include <linux/device.h>

#include <linux/platform_device.h>
#include <linux/sysrq.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/serial_core.h>
#include <linux/serial.h>
#include <linux/delay.h>
#include <linux/clk.h>
#include <linux/console.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/hardware.h>
#include <asm/plat-s3c/regs-serial.h>
#include <asm/arch/regs-gpio.h>


#define DEV_NAME "gprs_uart" /* 设备名 */
/* 这里将串口的主设备号设为0,则串口设备编号由内核动态分配;你也可指定串口的设备编号 */
#define GPRS_UART_MAJOR 0 /* 主设备号 */
#define GPRS_UART_MINOR 0 /* 次设备号 */
#define GPRS_UART_FIFO_SIZE 16 /* 串口FIFO的大小 */
#define RXSTAT_DUMMY_READ (0x10000000)
#define MAP_SIZE (0x100) /* 要映射的串口IO内存区大小 */

/* 串口发送中断号 */
#define TX_IRQ(port) ((port)->irq + 1)
/* 串口接收中断号 */
#define RX_IRQ(port) ((port)->irq)

/* 允许串口接收字符的标志 */
#define tx_enabled(port) ((port)->unused[0])
/* 允许串口发送字符的标志 */
#define rx_enabled(port) ((port)->unused[1])

/* 获取寄存器地址 */
#define portaddr(port, reg) ((port)->membase + (reg))

/* 读8位宽的寄存器 */
#define rd_regb(port, reg) (ioread8(portaddr(port, reg)))
/* 读32位宽的寄存器 */
#define rd_regl(port, reg) (ioread32(portaddr(port, reg)))
/* 写8位宽的寄存器 */
#define wr_regb(port, reg, val) \
do { iowrite8(val, portaddr(port, reg)); } while(0)
/* 写32位宽的寄存器 */
#define wr_regl(port, reg, val) \
do { iowrite32(val, portaddr(port, reg)); } while(0)


/* 禁止串口发送数据 */
static void gprs_uart_stop_tx(struct uart_port *port)
{
	if (tx_enabled(port)) /* 若串口已启动发送 */
	{
		disable_irq(TX_IRQ(port)); /* 禁止发送中断 */
		tx_enabled(port) = 0; /* 设置串口为未启动发送 */
	}
}

/* 使能串口发送数据 */
static void gprs_uart_start_tx(struct uart_port *port)
{
	if (!tx_enabled(port)) /* 若串口未启动发送 */
	{
		enable_irq(TX_IRQ(port)); /* 使能发送中断 */
		tx_enabled(port) = 1; /* 设置串口为已启动发送 */
	}
}

/* 禁止串口接收数据 */
static void gprs_uart_stop_rx(struct uart_port *port)
{
	if (rx_enabled(port)) /* 若串口已启动接收 */
	{
		disable_irq(RX_IRQ(port)); /* 禁止接收中断 */
		rx_enabled(port) = 0; /* 设置串口为未启动接收 */
	}
}

/* 使能modem的状态信号 */
static void gprs_uart_enable_ms(struct uart_port *port)
{
}

/* 串口的Tx FIFO缓存是否为空 */
static unsigned int gprs_uart_tx_empty(struct uart_port *port)
{
	int ret = 1;
	unsigned long ufstat = rd_regl(port, S3C2410_UFSTAT);
	unsigned long ufcon = rd_regl(port, S3C2410_UFCON);
	
	if (ufcon & S3C2410_UFCON_FIFOMODE) /* 若使能了FIFO */
	{
		if ((ufstat & S3C2410_UFSTAT_TXMASK) != 0 || /* 0 <FIFO <=15 */
			(ufstat & S3C2410_UFSTAT_TXFULL)) /* FIFO满 */
			ret = 0;
	}
	else /* 若未使能了FIFO,则判断发送缓存和发送移位寄存器是否均为空 */
	{
		ret = rd_regl(port, S3C2410_UTRSTAT) & S3C2410_UTRSTAT_TXE;
	}
	
	return ret;
}

/* 获取串口modem控制,因为uart2无modem控制,所以CTS、DSR直接返回有效 */
static unsigned int gprs_uart_get_mctrl(struct uart_port *port)
{
	return (TIOCM_CTS | TIOCM_DSR | TIOCM_CAR);
}

/* 设置串口modem控制 */
static void gprs_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
	
}

/* 设置break信号 */
static void gprs_uart_break_ctl(struct uart_port *port, int break_state)
{
	unsigned long flags;
	unsigned int ucon;
	
	spin_lock_irqsave(&port->lock, flags);
	
	ucon = rd_regl(port, S3C2410_UCON);
	
	if (break_state)
		ucon |= S3C2410_UCON_SBREAK;
	else
		ucon &= ~S3C2410_UCON_SBREAK;
	
	wr_regl(port, S3C2410_UCON, ucon);
	
	spin_unlock_irqrestore(&port->lock, flags);
}

/* 返回Rx FIFO已存多少数据 */
static int gprs_uart_rx_fifocnt(unsigned long ufstat)
{
	/* 若Rx FIFO已满,返回FIFO的大小 */
	if (ufstat & S3C2410_UFSTAT_RXFULL)
		return GPRS_UART_FIFO_SIZE;
	
	/* 若FIFO未满,返回Rx FIFO已存了多少字节数据 */
	return (ufstat & S3C2410_UFSTAT_RXMASK) >> S3C2410_UFSTAT_RXSHIFT;
}

#define S3C2410_UERSTAT_PARITY (0x1000)

/* 串口接收中断处理函数,获取串口接收到的数据,并将这些数据递交给行规则层 */
static irqreturn_t gprs_uart_rx_chars(int irq, void *dev_id)
{
	struct uart_port *port = dev_id;
	struct tty_struct *tty = port->info->tty;
	unsigned int ufcon, ch, flag, ufstat, uerstat;
	int max_count = 64;
	
	/* 循环接收数据,最多一次中断接收64字节数据 */
	while (max_count-- > 0)
	{
		ufcon = rd_regl(port, S3C2410_UFCON);
		ufstat = rd_regl(port, S3C2410_UFSTAT);
		
		/* 若Rx FIFO无数据了,跳出循环 */
		if (gprs_uart_rx_fifocnt(ufstat) == 0)
			break;
		
		/* 读取Rx error状态寄存器 */
		uerstat = rd_regl(port, S3C2410_UERSTAT);
		/* 读取已接受到的数据 */
		ch = rd_regb(port, S3C2410_URXH);
		
		/* insert the character into the buffer */
		/* 先将tty标志设为正常 */
		flag = TTY_NORMAL;
		/* 递增接收字符计数器 */
		port->icount.rx++;
		
		/* 判断是否存在Rx error
		* if (unlikely(uerstat & S3C2410_UERSTAT_ANY))等同于
		* if (uerstat & S3C2410_UERSTAT_ANY)
		* 只是unlikely表示uerstat & S3C2410_UERSTAT_ANY的值为假的可能性大一些
		* 另外还有一个likely(value)表示value的值为真的可能性更大一些
		*/
		if (unlikely(uerstat & S3C2410_UERSTAT_ANY))
		{
			/* 若break错误,递增icount.brk计算器 */
			if (uerstat & S3C2410_UERSTAT_BREAK)
			{
				port->icount.brk++;
				if (uart_handle_break(port))
					goto ignore_char;
			}
			
			/* 若frame错误,递增icount.frame计算器 */
			if (uerstat & S3C2410_UERSTAT_FRAME)
				port->icount.frame++;
			/* 若overrun错误,递增icount.overrun计算器 */
			if (uerstat & S3C2410_UERSTAT_OVERRUN)
				port->icount.overrun++;
			
				/* 查看我们是否关心该Rx error
				* port->read_status_mask保存着我们感兴趣的Rx error status
			*/
			uerstat &= port->read_status_mask;
			
			/* 若我们关心该Rx error,则将flag设置为对应的error flag */
			if (uerstat & S3C2410_UERSTAT_BREAK)
				flag = TTY_BREAK;
			else if (uerstat & S3C2410_UERSTAT_PARITY)
				flag = TTY_PARITY;
			else if (uerstat & ( S3C2410_UERSTAT_FRAME | S3C2410_UERSTAT_OVERRUN))
				flag = TTY_FRAME;
		}
		
		/* 处理sys字符 */
		if (uart_handle_sysrq_char(port, ch))
			goto ignore_char;
		
		/* 将接收到的字符插入到tty设备的flip缓冲 */
		uart_insert_char(port, uerstat, S3C2410_UERSTAT_OVERRUN, ch, flag);
		
ignore_char:
		continue;
	}
	
	/* 刷新tty设备的flip缓冲,将接受到的数据传给行规则层 */
	tty_flip_buffer_push(tty);
	
	return IRQ_HANDLED;
}

/* 串口发送中断处理函数,将用户空间的数据(保存在环形缓冲xmit里)发送出去 */
static irqreturn_t gprs_uart_tx_chars(int irq, void *dev_id)
{
	struct uart_port *port = dev_id;
	struct circ_buf *xmit = &port->info->xmit; /* 获取环线缓冲 */
	int count = 256;
	
	/* 若设置了xChar字符 */
	if (port->x_char)
	{
		/* 将该xChar发送出去 */
		wr_regb(port, S3C2410_UTXH, port->x_char);
		/* 递增发送计数 */
		port->icount.tx++;
		/* 清除xChar */
		port->x_char = 0;
		/* 退出中断处理 */
		goto out;
	}
	
	/* 如果没有更多的字符需要发送(环形缓冲为空)，
	* 或者uart Tx已停止，
	* 则停止uart并退出中断处理函数
	*/
	if (uart_circ_empty(xmit) || uart_tx_stopped(port))
	{
		gprs_uart_stop_tx(port);
		goto out;
	}
	
	/* 循环发送数据,直到环形缓冲为空,最多一次中断发送256字节数据 */
	while (!uart_circ_empty(xmit) && count-- > 0)
	{
		/* 若Tx FIFO已满,退出循环 */
		if (rd_regl(port, S3C2410_UFSTAT) & S3C2410_UFSTAT_TXFULL)
			break;
		
		/* 将要发送的数据写入Tx FIFO */
		wr_regb(port, S3C2410_UTXH, xmit->buf[xmit->tail]);
		/* 移向循环缓冲中下一要发送的数据 */
		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
		port->icount.tx++;
	}
	
	/* 如果环形缓冲区中剩余的字符少于WAKEUP_CHARS，唤醒上层 */
	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
		uart_write_wakeup(port);
	
	/* 如果环形缓冲为空，则停止发送 */
	if (uart_circ_empty(xmit))
		gprs_uart_stop_tx(port);
	
out:
	return IRQ_HANDLED;
}

/* 启动串口端口,在打开该驱动的设备文件时会调用该函数来申请串口中断,并设置串口为可接受,也可发送 */
static int gprs_uart_startup(struct uart_port *port)
{
	unsigned long flags;
	int ret;
	const char *portname = to_platform_device(port->dev)->name;
	
	/* 设置串口为不可接受,也不可发送 */
	rx_enabled(port) = 0;
	tx_enabled(port) = 0;
	
	spin_lock_irqsave(&port->lock, flags);
	
	/* 申请接收中断 */
	ret = request_irq(RX_IRQ(port), gprs_uart_rx_chars, 0, portname, port);
	if (ret != 0)
	{
		printk(KERN_ERR "cannot get irq %d\n", RX_IRQ(port));
		return ret;
	}
	
	/* 设置串口为允许接收 */
	rx_enabled(port) = 1;
	
	/* 申请发送中断 */
	ret = request_irq(TX_IRQ(port), gprs_uart_tx_chars, 0, portname, port);
	if (ret)
	{
		printk(KERN_ERR "cannot get irq %d\n", TX_IRQ(port));
		rx_enabled(port) = 0;
		free_irq(RX_IRQ(port), port);
		goto err;
	}
	
	/* 设置串口为允许发送 */
	tx_enabled(port) = 1;
	
err:
	spin_unlock_irqrestore(&port->lock, flags);
	return ret;
}

/* 关闭串口,在关闭驱动的设备文件时会调用该函数,释放串口中断 */

static void gprs_uart_shutdown(struct uart_port *port)
{
	rx_enabled(port) = 0; /* 设置串口为不允许接收 */
	free_irq(RX_IRQ(port), port); /* 释放接收中断 */
	tx_enabled(port) = 0; /* 设置串口为不允许发送 */
	free_irq(TX_IRQ(port), port); /* 释放发送中断 */
}

/* 设置串口参数 */
static void gprs_uart_set_termios(struct uart_port *port,
								  struct ktermios *termios,
								  struct ktermios *old)
{
	unsigned long flags;
	unsigned int baud, quot;
	unsigned int ulcon, ufcon = 0;
	
	/* 不支持moden控制信号线
	* HUPCL: 关闭时挂断moden
	* CMSPAR: mark or space (stick) parity
	* CLOCAL: 忽略任何moden控制线
	*/
	termios->c_cflag &= ~(HUPCL | CMSPAR);
	termios->c_cflag |= CLOCAL;
	
	/* 获取用户设置的串口波特率,并计算分频数(串口波特率除数quot) */
	baud = uart_get_baud_rate(port, termios, old, 0, 115200*8);
	if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST)
		quot = port->custom_divisor;
	else
		quot = port->uartclk / baud / 16 - 1;
	
	/* 设置数据字长 */
	switch (termios->c_cflag & CSIZE)
	{
	case CS5:
		ulcon = S3C2410_LCON_CS5;
		break;
	case CS6:
		ulcon = S3C2410_LCON_CS6;
		break;
	case CS7:
		ulcon = S3C2410_LCON_CS7;
		break;
	case CS8:
	default:
		ulcon = S3C2410_LCON_CS8;
		break;
	}
	
	/* 是否要求设置两个停止位(CSTOPB) */
	if (termios->c_cflag & CSTOPB)
		ulcon |= S3C2410_LCON_STOPB;
	
	/* 是否使用奇偶检验 */
	if (termios->c_cflag & PARENB)
	{
		if (termios->c_cflag & PARODD) /* 奇校验 */
			ulcon |= S3C2410_LCON_PODD;
		else /* 偶校验 */
			ulcon |= S3C2410_LCON_PEVEN;
	}
	else /* 无校验 */
	{
		ulcon |= S3C2410_LCON_PNONE;
	}
	
	if (port->fifosize > 1)
		ufcon |= S3C2410_UFCON_FIFOMODE | S3C2410_UFCON_RXTRIG8;
	
	spin_lock_irqsave(&port->lock, flags);
	
	/* 设置FIFO控制寄存器、线控制寄存器和波特率除数寄存器 */
	wr_regl(port, S3C2410_UFCON, ufcon);
	wr_regl(port, S3C2410_ULCON, ulcon);
	wr_regl(port, S3C2410_UBRDIV, quot);
	
	/* 更新串口FIFO的超时时限 */
	uart_update_timeout(port, termios->c_cflag, baud);
	
	/* 设置我们感兴趣的Rx error */
	port->read_status_mask = S3C2410_UERSTAT_OVERRUN;
	if (termios->c_iflag & INPCK)
		port->read_status_mask |= S3C2410_UERSTAT_FRAME | S3C2410_UERSTAT_PARITY;
	
	/* 设置我们忽略的Rx error */
	port->ignore_status_mask = 0;
	if (termios->c_iflag & IGNPAR)
		port->ignore_status_mask |= S3C2410_UERSTAT_OVERRUN;
	if (termios->c_iflag & IGNBRK && termios->c_iflag & IGNPAR)
		port->ignore_status_mask |= S3C2410_UERSTAT_FRAME;
	
	/* 若未设置CREAD(使用接收器),则忽略所有Rx error*/
	if ((termios->c_cflag & CREAD) == 0)
		port->ignore_status_mask |= RXSTAT_DUMMY_READ;
	
	spin_unlock_irqrestore(&port->lock, flags);
}

/* 获取串口类型 */
static const char *gprs_uart_type(struct uart_port *port)
{/* 返回描述串口类型的字符串指针 */
	return port->type == PORT_S3C2410 ? "gprs_uart:s3c2410_uart2" : NULL;
}

/* 申请串口一些必要的资源,如IO端口/IO内存资源,必要时还可以重新映射串口端口 */

static int gprs_uart_request_port(struct uart_port *port)
{
	struct resource *res;
	const char *name = to_platform_device(port->dev)->name;
	
	/* request_mem_region请求分配IO内存,从开始port->mapbase,大小MAP_SIZE
	* port->mapbase保存当前串口的寄存器基地址(物理)
	* uart2: 0x50008000
	*/
	
	res = request_mem_region(port->mapbase, MAP_SIZE, name);
	if (res == NULL)
	{
		printk(KERN_ERR"request_mem_region error: %p\n", res);
		return -EBUSY;
	}
	
	return 0;
}

/* 释放串口已申请的IO端口/IO内存资源,必要时还需iounmap */
static void gprs_uart_release_port(struct uart_port *port)
{
	/* 释放已分配IO内存 */
	release_mem_region(port->mapbase, MAP_SIZE);
}

/* 执行串口所需的自动配置 */
static void gprs_uart_config_port(struct uart_port *port, int flags)
{
	int retval;
	
	/* 请求串口 */
	retval = gprs_uart_request_port(port);
	/* 设置串口类型 */
	if (flags & UART_CONFIG_TYPE && retval == 0)
		port->type = PORT_S3C2410;
}

/* The UART operations structure */
static struct uart_ops gprs_uart_ops = {
	.start_tx = gprs_uart_start_tx, /* Start transmitting */
		.stop_tx = gprs_uart_stop_tx, /* Stop transmission */
		.stop_rx = gprs_uart_stop_rx, /* Stop reception */
		.enable_ms = gprs_uart_enable_ms, /* Enable modem status signals */
		.tx_empty = gprs_uart_tx_empty, /* Transmitter busy? */
		.get_mctrl = gprs_uart_get_mctrl, /* Get modem control */
		.set_mctrl = gprs_uart_set_mctrl, /* Set modem control */
		.break_ctl = gprs_uart_break_ctl, /* Set break signal */
		.startup = gprs_uart_startup, /* App opens GPRS_UART */
		.shutdown = gprs_uart_shutdown, /* App closes GPRS_UART */
		.set_termios = gprs_uart_set_termios, /* Set termios */
		.type = gprs_uart_type, /* Get UART type */
		.request_port = gprs_uart_request_port, /* Claim resources associated with a GPRS_UART port */
		.release_port = gprs_uart_release_port, /* Release resources associated with a GPRS_UART port */
		.config_port = gprs_uart_config_port, /* Configure when driver adds a GPRS_UART port */
};

/* Uart driver for GPRS_UART */
static struct uart_driver gprs_uart_driver = {
	.owner = THIS_MODULE, /* Owner */
		.driver_name = DEV_NAME, /* Driver name */
		.dev_name = DEV_NAME, /* Device node name */
		.major = GPRS_UART_MAJOR, /* Major number */
		.minor = GPRS_UART_MINOR, /* Minor number start */
		.nr = 1, /* Number of UART ports */
};

/* Uart port for GPRS_UART port */
static struct uart_port gprs_uart_port = {
	.irq = IRQ_S3CUART_RX2, /* IRQ */
		.fifosize = GPRS_UART_FIFO_SIZE, /* Size of the FIFO */
		.iotype = UPIO_MEM, /* IO memory */
		.flags = UPF_BOOT_AUTOCONF, /* UART port flag */
		.ops = &gprs_uart_ops, /* UART operations */
		.line = 0, /* UART port number */
		.lock = __SPIN_LOCK_UNLOCKED(gprs_uart_port.lock),
};

/* 初始化指定串口端口 */
static int gprs_uart_init_port(struct uart_port *port, struct platform_device *platdev)
{
	unsigned long flags;
	unsigned int gphcon;
	
	if (platdev == NULL)
		return -ENODEV;
	
	port->dev = &platdev->dev;
	
	/* 设置串口波特率时钟频率 */
	port->uartclk = clk_get_rate(clk_get(&platdev->dev, "pclk"));
	
	/* 设置串口的寄存器基地址(物理): 0x50008000 */
	port->mapbase = S3C2410_PA_UART2;
	
	/* 设置当前串口的寄存器基地址(虚拟): 0xF5008000 */
	port->membase = S3C24XX_VA_UART + (S3C2410_PA_UART2 - S3C24XX_PA_UART);
	
	spin_lock_irqsave(&port->lock, flags);
	
	wr_regl(port, S3C2410_UCON, S3C2410_UCON_DEFAULT);
	wr_regl(port, S3C2410_ULCON, S3C2410_LCON_CS8 | S3C2410_LCON_PNONE);
	wr_regl(port, S3C2410_UFCON, S3C2410_UFCON_FIFOMODE
		| S3C2410_UFCON_RXTRIG8 | S3C2410_UFCON_RESETBOTH);
	
	/* 将I/O port H的gph6和gph7设置为TXD2和RXD2 */
	gphcon = readl(S3C2410_GPHCON);
	gphcon &= ~((0x5) << 12);
	writel(gphcon, S3C2410_GPHCON);
	
	spin_unlock_irqrestore(&port->lock, flags);
	
	return 0;
}

/* Platform driver probe */
static int __init gprs_uart_probe(struct platform_device *dev)
{
	int ret;
	
	/* 初始化串口 */
	ret = gprs_uart_init_port(&gprs_uart_port, dev);
	if (ret < 0)
	{
		printk(KERN_ERR"gprs_uart_probe: gprs_uart_init_port error: %d\n", ret);
		return ret;
	}
	
	/* 添加串口 */
	ret = uart_add_one_port(&gprs_uart_driver, &gprs_uart_port);
	if (ret < 0)
	{
		printk(KERN_ERR"gprs_uart_probe: uart_add_one_port error: %d\n", ret);
		return ret;
	}
	
	/* 将串口uart_port结构体保存在platform_device->dev->driver_data中 */
	platform_set_drvdata(dev, &gprs_uart_port);
	
	return 0;
}

/* Called when the platform driver is unregistered */
static int gprs_uart_remove(struct platform_device *dev)
{
	platform_set_drvdata(dev, NULL);
	
	/* 移除串口 */
	uart_remove_one_port(&gprs_uart_driver, &gprs_uart_port);
	return 0;
}

/* Suspend power management event */
static int gprs_uart_suspend(struct platform_device *dev, pm_message_t state)
{
	uart_suspend_port(&gprs_uart_driver, &gprs_uart_port);
	return 0;
}

/* Resume after a previous suspend */
static int gprs_uart_resume(struct platform_device *dev)
{
	uart_resume_port(&gprs_uart_driver, &gprs_uart_port);
	return 0;
}

/* Platform driver for GPRS_UART */
static struct platform_driver gprs_plat_driver = {
	.probe = gprs_uart_probe, /* Probe method */
		.remove = __exit_p(gprs_uart_remove), /* Detach method */
		.suspend = gprs_uart_suspend, /* Power suspend */
		.resume = gprs_uart_resume, /* Resume after a suspend */
		.driver = {
		.owner = THIS_MODULE,
			.name = DEV_NAME, /* Driver name */
	},
};

/* Platform device for GPRS_UART */
struct platform_device *gprs_plat_device;

static int __init gprs_init_module(void)
{
	int retval;
	
	/* Register uart_driver for GPRS_UART */
	retval = uart_register_driver(&gprs_uart_driver);
	if (0 != retval)
	{
		printk(KERN_ERR "gprs_init_module: can't register the GPRS_UART driver %d\n",retval);
		return retval;
	}
	
	/* Register platform device for GPRS_UART. Usually called
	during architecture-specific setup */
	gprs_plat_device = platform_device_register_simple(DEV_NAME, 0, NULL, 0);
	if (IS_ERR(gprs_plat_device))
	{
		retval = PTR_ERR(gprs_plat_device);
		printk(KERN_ERR "gprs_init_module: can't register platform device %d\n", retval);
		goto fail_reg_plat_dev;
	}
	
	/* Announce a matching driver for the platform
	devices registered above */
	retval = platform_driver_register(&gprs_plat_driver);
	if (0 != retval)
	{
		printk(KERN_ERR "gprs_init_module: can't register platform driver %d\n", retval);
		goto fail_reg_plat_drv;
	}
	
	return 0; /* succeed */
	
fail_reg_plat_drv:
	platform_device_unregister(gprs_plat_device);
fail_reg_plat_dev:
	uart_unregister_driver(&gprs_uart_driver);
	return retval;
}

static void __exit gprs_exit_module(void)
{
/* The order of unregistration is important. Unregistering the
	UART driver before the platform driver will crash the system */
	
	/* Unregister the platform driver */
	platform_driver_unregister(&gprs_plat_driver);
	
	/* Unregister the platform devices */
	platform_device_unregister(gprs_plat_device);
	
	/* Unregister the GPRS_UART driver */
	uart_unregister_driver(&gprs_uart_driver);
}

module_init(gprs_init_module);
module_exit(gprs_exit_module);

MODULE_AUTHOR("");
MODULE_LICENSE("Dual BSD/GPL");