对于驱动的学习停歇了几乎一周的时间，期间忙于补习Linux应用编程和搜索驱动、内核相关书籍，以便之后更进一步地学习。在之前友善提供的驱动例程里面，涉及的知识面非常有限，需要研究更多的驱动源码，了解更多的驱动知识，是当务之急。研究别人代码的同时，当然不忘自己也要动手练习。以下贴出串口驱动程序，并在程序里附上简要注释。

 

/* linux/drivers/serial/s3c2440.c** Driver for Samsung S3C2440 and S3C2442 SoC onboard UARTs.** Ben Dooks, Copyright (c) 2003-2005,2008 Simtec Electronics* http://armlinux.simtec.co.uk/** This program is free software; you can redistribute it and/or modify* it under the terms of the GNU General Public License version 2 as* published by the Free Software Foundation. */#include <linux/module.h> #include <linux/ioport.h> #include <linux/io.h> #include <linux/platform_device.h> #include <linux/init.h> #include <linux/serial_core.h> #include <linux/serial.h>#include <asm/irq.h> #include <mach/hardware.h>#include <plat/regs-serial.h> #include <mach/regs-gpio.h>#include "samsung.h"static int s3c2440_serial_setsource(struct uart_port *port,struct s3c24xx_uart_clksrc *clk) { //本函数选定串口端口和时钟源unsigned long ucon = rd_regl(port, S3C2410_UCON); //读取寄存器UCON/* todo - proper fclk<>nonfclk switch. */ucon &= ~S3C2440_UCON_CLKMASK; //#define S3C2440_UCON_CLKMASK (3<<10)if (strcmp(clk->name, "uclk") == 0) //选择时钟源ucon |= S3C2440_UCON_UCLK;else if (strcmp(clk->name, "pclk") == 0)ucon |= S3C2440_UCON_PCLK;else if (strcmp(clk->name, "fclk") == 0)ucon |= S3C2440_UCON_FCLK;else {printk(KERN_ERR "unknown clock source %s/n", clk->name);return -EINVAL;}wr_regl(port, S3C2410_UCON, ucon); //把设置过的ucon写回串口控制寄存器return 0; }static int s3c2440_serial_getsource(struct uart_port *port,struct s3c24xx_uart_clksrc *clk) { //设置时钟源和对应预分频值unsigned long ucon = rd_regl(port, S3C2410_UCON);unsigned long ucon0, ucon1, ucon2;switch (ucon & S3C2440_UCON_CLKMASK) {case S3C2440_UCON_UCLK:clk->divisor = 1;clk->name = "uclk";break;case S3C2440_UCON_PCLK:case S3C2440_UCON_PCLK2:clk->divisor = 1;clk->name = "pclk";break;case S3C2440_UCON_FCLK:/* the fun of calculating the uart divisors on* the s3c2440 */ucon0 = __raw_readl(S3C24XX_VA_UART0 + S3C2410_UCON);ucon1 = __raw_readl(S3C24XX_VA_UART1 + S3C2410_UCON);ucon2 = __raw_readl(S3C24XX_VA_UART2 + S3C2410_UCON);printk("ucons: %08lx, %08lx, %08lx/n", ucon0, ucon1, ucon2);ucon0 &= S3C2440_UCON0_DIVMASK;ucon1 &= S3C2440_UCON1_DIVMASK;ucon2 &= S3C2440_UCON2_DIVMASK;if (ucon0 != 0) {clk->divisor = ucon0 >> S3C2440_UCON_DIVSHIFT;clk->divisor += 6;} else if (ucon1 != 0) {clk->divisor = ucon1 >> S3C2440_UCON_DIVSHIFT;clk->divisor += 21;} else if (ucon2 != 0) {clk->divisor = ucon2 >> S3C2440_UCON_DIVSHIFT;clk->divisor += 36;} else {/* manual calims 44, seems to be 9 */clk->divisor = 9;}clk->name = "fclk";break;}return 0; }static int s3c2440_serial_resetport(struct uart_port *port,struct s3c2410_uartcfg *cfg) { //重设串口unsigned long ucon = rd_regl(port, S3C2410_UCON);dbg("s3c2440_serial_resetport: port=%p (%08lx), cfg=%p/n",port, port->mapbase, cfg);/* ensure we don't change the clock settings... */ucon &= (S3C2440_UCON0_DIVMASK | (3<<10)); wr_regl(port, S3C2410_UCON, ucon | cfg->ucon); //重新设置寄存器UCONwr_regl(port, S3C2410_ULCON, cfg->ulcon); //重新设置寄存器ULCON/* reset both fifos */wr_regl(port, S3C2410_UFCON, cfg->ufcon | S3C2410_UFCON_RESETBOTH); //重启fifowr_regl(port, S3C2410_UFCON, cfg->ufcon); //重新设定寄存器UFCONreturn 0; }static struct s3c24xx_uart_info s3c2440_uart_inf = { //串口设备环境信息和提供的操作函数.name = "Samsung S3C2440 UART",.type = PORT_S3C2440,.fifosize = 64, .rx_fifomask = S3C2440_UFSTAT_RXMASK,.rx_fifoshift = S3C2440_UFSTAT_RXSHIFT,.rx_fifofull = S3C2440_UFSTAT_RXFULL,.tx_fifofull = S3C2440_UFSTAT_TXFULL,.tx_fifomask = S3C2440_UFSTAT_TXMASK,.tx_fifoshift = S3C2440_UFSTAT_TXSHIFT,.get_clksrc = s3c2440_serial_getsource,.set_clksrc = s3c2440_serial_setsource,.reset_port = s3c2440_serial_resetport, };/* device management */static int s3c2440_serial_probe(struct platform_device *dev) { //完成串口的添加dbg("s3c2440_serial_probe: dev=%p/n", dev);return s3c24xx_serial_probe(dev, &s3c2440_uart_inf); }static struct platform_driver s3c2440_serial_driver = { //注册串口设备.probe = s3c2440_serial_probe,.remove = __devexit_p(s3c24xx_serial_remove),.driver = {.name = "s3c2440-uart",.owner = THIS_MODULE,}, };s3c24xx_console_init(&s3c2440_serial_driver, &s3c2440_uart_inf);static int __init s3c2440_serial_init(void) { //初始化模块return s3c24xx_serial_init(&s3c2440_serial_driver, &s3c2440_uart_inf); }static void __exit s3c2440_serial_exit(void) { //退出模块platform_driver_unregister(&s3c2440_serial_driver); //注销串口设备 }module_init(s3c2440_serial_init); module_exit(s3c2440_serial_exit);MODULE_DESCRIPTION("Samsung S3C2440,S3C2442 SoC Serial port driver"); MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>"); MODULE_LICENSE("GPL v2"); MODULE_ALIAS("platform:s3c2440-uart");

 

 

几个问题需要我们注意：

1.设备如何注册、注销

串口驱动被作为一个单独的模块被加载进内核，在模块的加载和卸载函数中，只需注册和注销一个platform_driver结构体。

注册：

static struct platform_driver s3c2440_serial_driver = {.probe = s3c2440_serial_probe,.remove = __devexit_p(s3c24xx_serial_remove),.driver = {.name = "s3c2440-uart",.owner = THIS_MODULE,}, };

 

注销：

platform_driver_unregister(&s3c2440_serial_driver);

 

2.几个非常重要的结构体

s3c2410_uartcfg ：保存ucon ulcon ufcon三个串口寄存器的值

struct s3c2410_uartcfg {unsigned char hwport; /* hardware port number */unsigned char unused;unsigned short flags;upf_t uart_flags; /* default uart flags */unsigned int has_fracval;unsigned long ucon; /* value of ucon for port */unsigned long ulcon; /* value of ulcon for port */unsigned long ufcon; /* value of ufcon for port */struct s3c24xx_uart_clksrc *clocks;unsigned int clocks_size; };

 

 

s3c24xx_uart_info ：提供串口设备环境信息，并提供三个函数的接口

struct s3c24xx_uart_info {char *name;unsigned int type;unsigned int fifosize;unsigned long rx_fifomask;unsigned long rx_fifoshift;unsigned long rx_fifofull;unsigned long tx_fifomask;unsigned long tx_fifoshift;unsigned long tx_fifofull;/* uart port features */unsigned int has_divslot:1;/* clock source control */int (*get_clksrc)(struct uart_port *, struct s3c24xx_uart_clksrc *clk);int (*set_clksrc)(struct uart_port *, struct s3c24xx_uart_clksrc *clk);/* uart controls */int (*reset_port)(struct uart_port *, struct s3c2410_uartcfg *); };

 

 

platform_device ：设备的信息

 struct platform_device {const char * name;int id;struct device dev;u32 num_resources;struct resource * resource;const struct platform_device_id *id_entry;/* arch specific additions */struct pdev_archdata archdata; };

 

 

platform_driver ：设备注册用

struct platform_driver {int (*probe)(struct platform_device *);int (*remove)(struct platform_device *);void (*shutdown)(struct platform_device *);int (*suspend)(struct platform_device *, pm_message_t state);int (*resume)(struct platform_device *);struct device_driver driver;const struct platform_device_id *id_table; };

 

 

3.读写寄存器的宏定义

（1）读寄存器

unsigned long ucon = rd_regl(port, S3C2410_UCON);

 

#define rd_regl(port, reg)      (__raw_readl(portaddr(port, reg)))

static unsigned char __raw_readb(unsigned int ptr)

{

       return *((volatile unsigned char *)ptr);

}

#define portaddr(port, reg)    ((port)->membase + (reg))

（2）写寄存器

wr_regl(port, S3C2410_UCON, ucon);

#define wr_regl(port, reg, val)   __raw_writel(val, portaddr(port, reg))

#define portaddr(port, reg)          ((port)->membase + (reg))

#define __raw_writel(v,p)           (*(unsigned long *)(p) = (v))

 

4.函数的注册方式

     细心的朋友可能会发现，我们之前一直使用的是传统的 device driver 机制(通过 driver_register 函数进行注册)本串口所使用的是一个设备用 Platform_device 表示，驱动用 Platform_driver 进行注册的机制。而后者是在内核2.6版本所提出来的新事物，其优势在于platform机制将设备本身的资源注册进内核，由内核统一管理，在驱动程序中使用这些资源时通过 platform device 提供的标准接口进行申请并使用。这样提高了驱动和资源管理的独立性，并且拥有较好的可移植性和安全性(这些标准接口是安全的)。关于这两种机制更深入的分析，请看以下链接：http://blog.csdn.net/jarvis_xian/archive/2011/05/23/6440649.aspx