串口驱动

 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
 *
 *
 * 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
#include
#include
#include
#include
#include
#include

#include
#include

#include
#include

#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UCON
    wr_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fifo
    wr_regl(port, S3C2410_UFCON, cfg->ufcon);         //重新设定寄存器UFCON

    return 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 ");
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