PLATFORM设备驱动

　　字符设备，杂项设备虽然简单，但是在工程中，比如SDK中，通常都使用platform设备驱动来实现硬件驱动，为什么呢？先看看platform设备驱动的结构：

　　platform由两部分组成：设备--platform_device和驱动--platform_driver。它们之间通过platform总线来绑定，这个我们不需要关心，内核里面的东西。

　　platform总线是一个虚拟的总线，跟其他总线（比如：I2C,SPI,USB,PCIE）一样，当系统注册一个设备（platform_device）的时候，会通过它去寻找与之匹配的驱动（platform_driver）；当注册一个驱动(platform_driver)的时候，也会通过platform总线去寻找一个相应的设备（platform_device）。

　　platform设备在注册的时候，将其使用的资源也注册进去，由内核统一管理，在 驱动程序 使用这些资源时 使用统一的接口，这样提高了程序的可移植性。

 　　好吧，看看相关的结构体吧。

struct platform_device {  

　　    const char    * name ;  /* 设备名 */  

    　　int    id ;   //  设备名编号， 配合设备名使用   

    　　struct device    dev ;  

    　　u32    num_resources ;  

    　　struct resource    * resource ;   /* 设备资源 */  

　　}

　　struct resource {  

　　    resource_size_t start; /* 资源的起始物理地址 */  

　　    resource_size_t end;   <span style="font-family: Arial, Helvetica, sans-serif; font-size: 12px;">/* 资源的结束物理地址 */  

　　    const char      *name;  /* 资源的名称 */  

　　    unsigned long   flags;   /* 资源的类型，比如MEM ，IO，IRQ类型 */  

　　    struct resource *parent, *sibling, *child; /* 资源链表指针 */  

　　};  

　　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 (*suspend_late)(struct platform_device *, pm_message_t state);  

　　        int (*resume_early)(struct platform_device *);  

　　        int (*resume)(struct platform_device *);  

        　　struct device_driver driver;  

　　};  

　　这就是最基础的三个结构体，把这三个结构体里面的部分或全部成员填满，一个platform设备驱动就基本完成了。

　　和字符驱动一样，看流程吧：

　　1，先定义，再注册device，一般的我们可以放在板文件里。

　　在dev-rtc.c文件中：

static struct resource s3c_rtc_resource[] = {
    [0] = {
        .start    = S3C_PA_RTC,
        .end    = S3C_PA_RTC + 0xff,
        .flags    = IORESOURCE_MEM,
    },
    [1] = {
        .start    = IRQ_RTC_ALARM,
        .end    = IRQ_RTC_ALARM,
        .flags    = IORESOURCE_IRQ,
    },
    [2] = {
        .start    = IRQ_RTC_TIC,
        .end    = IRQ_RTC_TIC,
        .flags    = IORESOURCE_IRQ
    }
};

struct platform_device s3c_device_rtc = {
    .name        = "s3c64xx-rtc",
    .id        = -1,
    .num_resources    = ARRAY_SIZE(s3c_rtc_resource),
    .resource    = s3c_rtc_resource,
};
EXPORT_SYMBOL(s3c_device_rtc);

　　在这里我们看到一个设备struct platform_device s3c_device_rtc，以及它用到的resource。刚我说了，一般device是在板级文件中定义和注册，但是这个是作为系统的rtc，它就有了它专门定义的文件，但是它在这里导出（EXPORT_SYMBOL(s3c_device_rtc)），注册在哪呢？这回真的在板文件了

/* Add platform device */
static struct platform_device *xc2440_devices[] __initdata = {
    &s3c_device_nand,
    &s3c_device_lcd,
    &s3c_device_adc,
    &s3c_device_hwmon,
    &s3c_device_ts,    
    &xc2440_ethernet_device,
    &s3c_device_ohci,
    &s3c_device_usbgadget,
    &s3c_device_timer[0],
    &s3c_device_timer[1],
    &xc2440_backlight_device,
    &xc2440_beeper_device,
    &xc2440_device_led,
    &xc2440_button_device,
    &s3c_device_i2c0,
    &s3c_device_rtc,
    &s3c_device_wdt,    
    &s3c_device_sdi,
    &s3c_device_iis,        
    &xc2440_audio_device,
    &xc2440_ds18b20_device,
    &xc2440_irm_device,

/*    &s3c_device_spi0,
    &s3c_device_spi1,
    &s3c_device_camif,
    &xc2440_spi_gpio, */

};

　　我们看到rtc的device在一个platform_device的数列里面，这样便于我们理解和移植。还是没注册啊~怎么那么啰嗦

static void __init xc2440_machine_init(void)
{
    s3c24xx_fb_set_platdata(&xc2440_fb_info);
    s3c_i2c0_set_platdata(NULL);
    s3c_nand_set_platdata(&xc2440_nand_info);
    s3c24xx_mci_set_platdata(&xc2440_mmc_cfg);
    s3c_hwmon_set_platdata(&xc2440_hwmon_info);
    s3c24xx_ts_set_platdata(&xc2440_ts_cfg);
    i2c_register_board_info(0, xc2440_i2c_devs,ARRAY_SIZE(xc2440_i2c_devs));
    s3c24xx_udc_set_platdata(&xc2440_udc_cfg);
    
    spi_register_board_info(xc2440_spi_board_info, ARRAY_SIZE(xc2440_spi_board_info));
    platform_add_devices(xc2440_devices, ARRAY_SIZE(xc2440_devices));
}

终于注册进去了、、、、、、、、

下面是应用中的一个设备定义，注册已经在上面了：

/* IRM3638 */
static struct platform_xc2440_irm_data xc2440_irm_pins = {
    .ctrl_pin_irq = IRQ_EINT(11),
    .irq_type     = IRQF_TRIGGER_FALLING,
};


static struct platform_device xc2440_irm_device = {
    .name        = "xc2440-irm",
    .id        = -1,
    .dev        = {
        .platform_data    = &xc2440_irm_pins,
    },
};

　　这个platform_device就没有resources，因为它不使用。但是它多了一个自己定义的结构体platform_xc2440_irm_data，作为与驱动交换数据。

2，platform_driver的编写。

　　实现跟字符驱动没什么区别，都需要完成file_operations这个结构体的成员函数。但是字符驱动的注册和卸载，放到了platform_driver结构体的probe和remove函数里。而驱动本身的注册和卸载就用到了platform_driver_register和platform_driver_unregister。

看一个刚才s3c的rtc程序，关于rtc相关的函数先略掉，主要看架构：

/* drivers/rtc/rtc-s3c.c
 *
 * Copyright (c) 2010 Samsung Electronics Co., Ltd.
 *        http://www.samsung.com/
 *
 * Copyright (c) 2004,2006 Simtec Electronics
 *    Ben Dooks, <ben@simtec.co.uk>
 *    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.
 *
 * S3C2410/S3C2440/S3C24XX Internal RTC Driver
*/

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/interrupt.h>
#include <linux/rtc.h>
#include <linux/bcd.h>
#include <linux/clk.h>
#include <linux/log2.h>
#include <linux/slab.h>

#include <mach/hardware.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <plat/regs-rtc.h>

enum s3c_cpu_type {
    TYPE_S3C2410,
    TYPE_S3C64XX,
};

/* I have yet to find an S3C implementation with more than one
 * of these rtc blocks in */

static struct resource *s3c_rtc_mem;

static struct clk *rtc_clk;
static void __iomem *s3c_rtc_base;
static int s3c_rtc_alarmno = NO_IRQ;
static int s3c_rtc_tickno  = NO_IRQ;
static enum s3c_cpu_type s3c_rtc_cpu_type;

static DEFINE_SPINLOCK(s3c_rtc_pie_lock);

/* IRQ Handlers */

static irqreturn_t s3c_rtc_alarmirq(int irq, void *id)
{
    struct rtc_device *rdev = id;

    rtc_update_irq(rdev, 1, RTC_AF | RTC_IRQF);

    if (s3c_rtc_cpu_type == TYPE_S3C64XX)
        writeb(S3C2410_INTP_ALM, s3c_rtc_base + S3C2410_INTP);

    return IRQ_HANDLED;
}

static irqreturn_t s3c_rtc_tickirq(int irq, void *id)
{
    struct rtc_device *rdev = id;

    rtc_update_irq(rdev, 1, RTC_PF | RTC_IRQF);

    if (s3c_rtc_cpu_type == TYPE_S3C64XX)
        writeb(S3C2410_INTP_TIC, s3c_rtc_base + S3C2410_INTP);

    return IRQ_HANDLED;
}

/* Update control registers */
static void s3c_rtc_setaie(int to)
{
    unsigned int tmp;

    pr_debug("%s: aie=%d
", __func__, to);

    tmp = readb(s3c_rtc_base + S3C2410_RTCALM) & ~S3C2410_RTCALM_ALMEN;

    if (to)
        tmp |= S3C2410_RTCALM_ALMEN;

    writeb(tmp, s3c_rtc_base + S3C2410_RTCALM);
}

static int s3c_rtc_setpie(struct device *dev, int enabled)
{
    unsigned int tmp;

    pr_debug("%s: pie=%d
", __func__, enabled);

    spin_lock_irq(&s3c_rtc_pie_lock);

    if (s3c_rtc_cpu_type == TYPE_S3C64XX) {
        tmp = readw(s3c_rtc_base + S3C2410_RTCCON);
        tmp &= ~S3C64XX_RTCCON_TICEN;

        if (enabled)
            tmp |= S3C64XX_RTCCON_TICEN;

        writew(tmp, s3c_rtc_base + S3C2410_RTCCON);
    } else {
        tmp = readb(s3c_rtc_base + S3C2410_TICNT);
        tmp &= ~S3C2410_TICNT_ENABLE;

        if (enabled)
            tmp |= S3C2410_TICNT_ENABLE;

        writeb(tmp, s3c_rtc_base + S3C2410_TICNT);
    }

    spin_unlock_irq(&s3c_rtc_pie_lock);

    return 0;
}

static int s3c_rtc_setfreq(struct device *dev, int freq)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct rtc_device *rtc_dev = platform_get_drvdata(pdev);
    unsigned int tmp = 0;

    if (!is_power_of_2(freq))
        return -EINVAL;

    spin_lock_irq(&s3c_rtc_pie_lock);

    if (s3c_rtc_cpu_type == TYPE_S3C2410) {
        tmp = readb(s3c_rtc_base + S3C2410_TICNT);
        tmp &= S3C2410_TICNT_ENABLE;
    }

    tmp |= (rtc_dev->max_user_freq / freq)-1;

    writel(tmp, s3c_rtc_base + S3C2410_TICNT);
    spin_unlock_irq(&s3c_rtc_pie_lock);

    return 0;
}

/* Time read/write */

static int s3c_rtc_gettime(struct device *dev, struct rtc_time *rtc_tm)
{
    unsigned int have_retried = 0;
    void __iomem *base = s3c_rtc_base;

 retry_get_time:
    rtc_tm->tm_min  = readb(base + S3C2410_RTCMIN);
    rtc_tm->tm_hour = readb(base + S3C2410_RTCHOUR);
    rtc_tm->tm_mday = readb(base + S3C2410_RTCDATE);
    rtc_tm->tm_mon  = readb(base + S3C2410_RTCMON);
    rtc_tm->tm_year = readb(base + S3C2410_RTCYEAR);
    rtc_tm->tm_sec  = readb(base + S3C2410_RTCSEC);

    /* the only way to work out wether the system was mid-update
     * when we read it is to check the second counter, and if it
     * is zero, then we re-try the entire read
     */

    if (rtc_tm->tm_sec == 0 && !have_retried) {
        have_retried = 1;
        goto retry_get_time;
    }

    pr_debug("read time %04d.%02d.%02d %02d:%02d:%02d
",
         1900 + rtc_tm->tm_year, rtc_tm->tm_mon, rtc_tm->tm_mday,
         rtc_tm->tm_hour, rtc_tm->tm_min, rtc_tm->tm_sec);

    rtc_tm->tm_sec = bcd2bin(rtc_tm->tm_sec);
    rtc_tm->tm_min = bcd2bin(rtc_tm->tm_min);
    rtc_tm->tm_hour = bcd2bin(rtc_tm->tm_hour);
    rtc_tm->tm_mday = bcd2bin(rtc_tm->tm_mday);
    rtc_tm->tm_mon = bcd2bin(rtc_tm->tm_mon);
    rtc_tm->tm_year = bcd2bin(rtc_tm->tm_year);

    rtc_tm->tm_year += 100;
    rtc_tm->tm_mon -= 1;

    return rtc_valid_tm(rtc_tm);
}

static int s3c_rtc_settime(struct device *dev, struct rtc_time *tm)
{
    void __iomem *base = s3c_rtc_base;
    int year = tm->tm_year - 100;

    pr_debug("set time %04d.%02d.%02d %02d:%02d:%02d
",
         1900 + tm->tm_year, tm->tm_mon, tm->tm_mday,
         tm->tm_hour, tm->tm_min, tm->tm_sec);

    /* we get around y2k by simply not supporting it */

    if (year < 0 || year >= 100) {
        dev_err(dev, "rtc only supports 100 years
");
        return -EINVAL;
    }

    writeb(bin2bcd(tm->tm_sec),  base + S3C2410_RTCSEC);
    writeb(bin2bcd(tm->tm_min),  base + S3C2410_RTCMIN);
    writeb(bin2bcd(tm->tm_hour), base + S3C2410_RTCHOUR);
    writeb(bin2bcd(tm->tm_mday), base + S3C2410_RTCDATE);
    writeb(bin2bcd(tm->tm_mon + 1), base + S3C2410_RTCMON);
    writeb(bin2bcd(year), base + S3C2410_RTCYEAR);

    return 0;
}

static int s3c_rtc_getalarm(struct device *dev, struct rtc_wkalrm *alrm)
{
    struct rtc_time *alm_tm = &alrm->time;
    void __iomem *base = s3c_rtc_base;
    unsigned int alm_en;

    alm_tm->tm_sec  = readb(base + S3C2410_ALMSEC);
    alm_tm->tm_min  = readb(base + S3C2410_ALMMIN);
    alm_tm->tm_hour = readb(base + S3C2410_ALMHOUR);
    alm_tm->tm_mon  = readb(base + S3C2410_ALMMON);
    alm_tm->tm_mday = readb(base + S3C2410_ALMDATE);
    alm_tm->tm_year = readb(base + S3C2410_ALMYEAR);

    alm_en = readb(base + S3C2410_RTCALM);

    alrm->enabled = (alm_en & S3C2410_RTCALM_ALMEN) ? 1 : 0;

    pr_debug("read alarm %d, %04d.%02d.%02d %02d:%02d:%02d
",
         alm_en,
         1900 + alm_tm->tm_year, alm_tm->tm_mon, alm_tm->tm_mday,
         alm_tm->tm_hour, alm_tm->tm_min, alm_tm->tm_sec);


    /* decode the alarm enable field */

    if (alm_en & S3C2410_RTCALM_SECEN)
        alm_tm->tm_sec = bcd2bin(alm_tm->tm_sec);
    else
        alm_tm->tm_sec = -1;

    if (alm_en & S3C2410_RTCALM_MINEN)
        alm_tm->tm_min = bcd2bin(alm_tm->tm_min);
    else
        alm_tm->tm_min = -1;

    if (alm_en & S3C2410_RTCALM_HOUREN)
        alm_tm->tm_hour = bcd2bin(alm_tm->tm_hour);
    else
        alm_tm->tm_hour = -1;

    if (alm_en & S3C2410_RTCALM_DAYEN)
        alm_tm->tm_mday = bcd2bin(alm_tm->tm_mday);
    else
        alm_tm->tm_mday = -1;

    if (alm_en & S3C2410_RTCALM_MONEN) {
        alm_tm->tm_mon = bcd2bin(alm_tm->tm_mon);
        alm_tm->tm_mon -= 1;
    } else {
        alm_tm->tm_mon = -1;
    }

    if (alm_en & S3C2410_RTCALM_YEAREN)
        alm_tm->tm_year = bcd2bin(alm_tm->tm_year);
    else
        alm_tm->tm_year = -1;

    return 0;
}

static int s3c_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
{
    struct rtc_time *tm = &alrm->time;
    void __iomem *base = s3c_rtc_base;
    unsigned int alrm_en;

    pr_debug("s3c_rtc_setalarm: %d, %04d.%02d.%02d %02d:%02d:%02d
",
         alrm->enabled,
         1900 + tm->tm_year, tm->tm_mon, tm->tm_mday,
         tm->tm_hour, tm->tm_min, tm->tm_sec);


    alrm_en = readb(base + S3C2410_RTCALM) & S3C2410_RTCALM_ALMEN;
    writeb(0x00, base + S3C2410_RTCALM);

    if (tm->tm_sec < 60 && tm->tm_sec >= 0) {
        alrm_en |= S3C2410_RTCALM_SECEN;
        writeb(bin2bcd(tm->tm_sec), base + S3C2410_ALMSEC);
    }

    if (tm->tm_min < 60 && tm->tm_min >= 0) {
        alrm_en |= S3C2410_RTCALM_MINEN;
        writeb(bin2bcd(tm->tm_min), base + S3C2410_ALMMIN);
    }

    if (tm->tm_hour < 24 && tm->tm_hour >= 0) {
        alrm_en |= S3C2410_RTCALM_HOUREN;
        writeb(bin2bcd(tm->tm_hour), base + S3C2410_ALMHOUR);
    }

    pr_debug("setting S3C2410_RTCALM to %08x
", alrm_en);

    writeb(alrm_en, base + S3C2410_RTCALM);

    s3c_rtc_setaie(alrm->enabled);

    return 0;
}

static int s3c_rtc_proc(struct device *dev, struct seq_file *seq)
{
    unsigned int ticnt;

    if (s3c_rtc_cpu_type == TYPE_S3C64XX) {
        ticnt = readw(s3c_rtc_base + S3C2410_RTCCON);
        ticnt &= S3C64XX_RTCCON_TICEN;
    } else {
        ticnt = readb(s3c_rtc_base + S3C2410_TICNT);
        ticnt &= S3C2410_TICNT_ENABLE;
    }

    seq_printf(seq, "periodic_IRQ	: %s
", ticnt  ? "yes" : "no");
    return 0;
}

static int s3c_rtc_open(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct rtc_device *rtc_dev = platform_get_drvdata(pdev);
    int ret;

    ret = request_irq(s3c_rtc_alarmno, s3c_rtc_alarmirq,
              IRQF_DISABLED,  "s3c2410-rtc alarm", rtc_dev);

    if (ret) {
        dev_err(dev, "IRQ%d error %d
", s3c_rtc_alarmno, ret);
        return ret;
    }

    ret = request_irq(s3c_rtc_tickno, s3c_rtc_tickirq,
              IRQF_DISABLED,  "s3c2410-rtc tick", rtc_dev);

    if (ret) {
        dev_err(dev, "IRQ%d error %d
", s3c_rtc_tickno, ret);
        goto tick_err;
    }

    return ret;

 tick_err:
    free_irq(s3c_rtc_alarmno, rtc_dev);
    return ret;
}

static void s3c_rtc_release(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct rtc_device *rtc_dev = platform_get_drvdata(pdev);

    /* do not clear AIE here, it may be needed for wake */

    s3c_rtc_setpie(dev, 0);
    free_irq(s3c_rtc_alarmno, rtc_dev);
    free_irq(s3c_rtc_tickno, rtc_dev);
}

static const struct rtc_class_ops s3c_rtcops = {
    .open        = s3c_rtc_open,
    .release    = s3c_rtc_release,
    .read_time    = s3c_rtc_gettime,
    .set_time    = s3c_rtc_settime,
    .read_alarm    = s3c_rtc_getalarm,
    .set_alarm    = s3c_rtc_setalarm,
    .irq_set_freq    = s3c_rtc_setfreq,
    .irq_set_state    = s3c_rtc_setpie,
    .proc        = s3c_rtc_proc,
    .alarm_irq_enable = s3c_rtc_setaie,
};

static void s3c_rtc_enable(struct platform_device *pdev, int en)
{
    void __iomem *base = s3c_rtc_base;
    unsigned int tmp;

    if (s3c_rtc_base == NULL)
        return;

    if (!en) {
        tmp = readw(base + S3C2410_RTCCON);
        if (s3c_rtc_cpu_type == TYPE_S3C64XX)
            tmp &= ~S3C64XX_RTCCON_TICEN;
        tmp &= ~S3C2410_RTCCON_RTCEN;
        writew(tmp, base + S3C2410_RTCCON);

        if (s3c_rtc_cpu_type == TYPE_S3C2410) {
            tmp = readb(base + S3C2410_TICNT);
            tmp &= ~S3C2410_TICNT_ENABLE;
            writeb(tmp, base + S3C2410_TICNT);
        }
    } else {
        /* re-enable the device, and check it is ok */

        if ((readw(base+S3C2410_RTCCON) & S3C2410_RTCCON_RTCEN) == 0) {
            dev_info(&pdev->dev, "rtc disabled, re-enabling
");

            tmp = readw(base + S3C2410_RTCCON);
            writew(tmp | S3C2410_RTCCON_RTCEN,
                base + S3C2410_RTCCON);
        }

        if ((readw(base + S3C2410_RTCCON) & S3C2410_RTCCON_CNTSEL)) {
            dev_info(&pdev->dev, "removing RTCCON_CNTSEL
");

            tmp = readw(base + S3C2410_RTCCON);
            writew(tmp & ~S3C2410_RTCCON_CNTSEL,
                base + S3C2410_RTCCON);
        }

        if ((readw(base + S3C2410_RTCCON) & S3C2410_RTCCON_CLKRST)) {
            dev_info(&pdev->dev, "removing RTCCON_CLKRST
");

            tmp = readw(base + S3C2410_RTCCON);
            writew(tmp & ~S3C2410_RTCCON_CLKRST,
                base + S3C2410_RTCCON);
        }
    }
}

static int __devexit s3c_rtc_remove(struct platform_device *dev)
{
    struct rtc_device *rtc = platform_get_drvdata(dev);

    platform_set_drvdata(dev, NULL);
    rtc_device_unregister(rtc);

    s3c_rtc_setpie(&dev->dev, 0);
    s3c_rtc_setaie(0);

    clk_disable(rtc_clk);
    clk_put(rtc_clk);
    rtc_clk = NULL;

    iounmap(s3c_rtc_base);
    release_resource(s3c_rtc_mem);
    kfree(s3c_rtc_mem);

    return 0;
}

static int __devinit s3c_rtc_probe(struct platform_device *pdev)
{
    struct rtc_device *rtc;
    struct rtc_time rtc_tm;
    struct resource *res;
    int ret;

    pr_debug("%s: probe=%p
", __func__, pdev);

    /* find the IRQs */

    s3c_rtc_tickno = platform_get_irq(pdev, 1);
    if (s3c_rtc_tickno < 0) {
        dev_err(&pdev->dev, "no irq for rtc tick
");
        return -ENOENT;
    }

    s3c_rtc_alarmno = platform_get_irq(pdev, 0);
    if (s3c_rtc_alarmno < 0) {
        dev_err(&pdev->dev, "no irq for alarm
");
        return -ENOENT;
    }

    pr_debug("s3c2410_rtc: tick irq %d, alarm irq %d
",
         s3c_rtc_tickno, s3c_rtc_alarmno);

    /* get the memory region */

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    if (res == NULL) {
        dev_err(&pdev->dev, "failed to get memory region resource
");
        return -ENOENT;
    }

    s3c_rtc_mem = request_mem_region(res->start,
                     res->end-res->start+1,
                     pdev->name);

    if (s3c_rtc_mem == NULL) {
        dev_err(&pdev->dev, "failed to reserve memory region
");
        ret = -ENOENT;
        goto err_nores;
    }

    s3c_rtc_base = ioremap(res->start, res->end - res->start + 1);
    if (s3c_rtc_base == NULL) {
        dev_err(&pdev->dev, "failed ioremap()
");
        ret = -EINVAL;
        goto err_nomap;
    }

    rtc_clk = clk_get(&pdev->dev, "rtc");
    if (IS_ERR(rtc_clk)) {
        dev_err(&pdev->dev, "failed to find rtc clock source
");
        ret = PTR_ERR(rtc_clk);
        rtc_clk = NULL;
        goto err_clk;
    }

    clk_enable(rtc_clk);

    /* check to see if everything is setup correctly */

    s3c_rtc_enable(pdev, 1);

    pr_debug("s3c2410_rtc: RTCCON=%02x
",
         readw(s3c_rtc_base + S3C2410_RTCCON));

    device_init_wakeup(&pdev->dev, 1);

    /* register RTC and exit */

    rtc = rtc_device_register("s3c", &pdev->dev, &s3c_rtcops,
                  THIS_MODULE);

    if (IS_ERR(rtc)) {
        dev_err(&pdev->dev, "cannot attach rtc
");
        ret = PTR_ERR(rtc);
        goto err_nortc;
    }

    s3c_rtc_cpu_type = platform_get_device_id(pdev)->driver_data;

    /* Check RTC Time */

    s3c_rtc_gettime(NULL, &rtc_tm);

    if (rtc_valid_tm(&rtc_tm)) {
        rtc_tm.tm_year    = 100;
        rtc_tm.tm_mon    = 0;
        rtc_tm.tm_mday    = 1;
        rtc_tm.tm_hour    = 0;
        rtc_tm.tm_min    = 0;
        rtc_tm.tm_sec    = 0;

        s3c_rtc_settime(NULL, &rtc_tm);

        dev_warn(&pdev->dev, "warning: invalid RTC value so initializing it
");
    }

    if (s3c_rtc_cpu_type == TYPE_S3C64XX)
        rtc->max_user_freq = 32768;
    else
        rtc->max_user_freq = 128;

    platform_set_drvdata(pdev, rtc);

    s3c_rtc_setfreq(&pdev->dev, 1);

    return 0;

 err_nortc:
    s3c_rtc_enable(pdev, 0);
    clk_disable(rtc_clk);
    clk_put(rtc_clk);

 err_clk:
    iounmap(s3c_rtc_base);

 err_nomap:
    release_resource(s3c_rtc_mem);

 err_nores:
    return ret;
}

#ifdef CONFIG_PM

/* RTC Power management control */

static int ticnt_save, ticnt_en_save;

static int s3c_rtc_suspend(struct platform_device *pdev, pm_message_t state)
{
    /* save TICNT for anyone using periodic interrupts */
    ticnt_save = readb(s3c_rtc_base + S3C2410_TICNT);
    if (s3c_rtc_cpu_type == TYPE_S3C64XX) {
        ticnt_en_save = readw(s3c_rtc_base + S3C2410_RTCCON);
        ticnt_en_save &= S3C64XX_RTCCON_TICEN;
    }
    s3c_rtc_enable(pdev, 0);

    if (device_may_wakeup(&pdev->dev))
        enable_irq_wake(s3c_rtc_alarmno);

    return 0;
}

static int s3c_rtc_resume(struct platform_device *pdev)
{
    unsigned int tmp;

    s3c_rtc_enable(pdev, 1);
    writeb(ticnt_save, s3c_rtc_base + S3C2410_TICNT);
    if (s3c_rtc_cpu_type == TYPE_S3C64XX && ticnt_en_save) {
        tmp = readw(s3c_rtc_base + S3C2410_RTCCON);
        writew(tmp | ticnt_en_save, s3c_rtc_base + S3C2410_RTCCON);
    }

    if (device_may_wakeup(&pdev->dev))
        disable_irq_wake(s3c_rtc_alarmno);

    return 0;
}
#else
#define s3c_rtc_suspend NULL
#define s3c_rtc_resume  NULL
#endif

static struct platform_device_id s3c_rtc_driver_ids[] = {
    {
        .name        = "s3c2410-rtc",
        .driver_data    = TYPE_S3C2410,
    }, {
        .name        = "s3c64xx-rtc",
        .driver_data    = TYPE_S3C64XX,
    },
    { }
};

MODULE_DEVICE_TABLE(platform, s3c_rtc_driver_ids);

static struct platform_driver s3c_rtc_driver = {
    .probe        = s3c_rtc_probe,
    .remove        = __devexit_p(s3c_rtc_remove),
    .suspend    = s3c_rtc_suspend,
    .resume        = s3c_rtc_resume,
    .id_table    = s3c_rtc_driver_ids,
    .driver        = {
        .name    = "s3c-rtc",
        .owner    = THIS_MODULE,
    },
};

static char __initdata banner[] = "S3C24XX RTC, (c) 2004,2006 Simtec Electronics
";

static int __init s3c_rtc_init(void)
{
    printk(banner);
    return platform_driver_register(&s3c_rtc_driver);
}

static void __exit s3c_rtc_exit(void)
{
    platform_driver_unregister(&s3c_rtc_driver);
}

module_init(s3c_rtc_init);
module_exit(s3c_rtc_exit);

MODULE_DESCRIPTION("Samsung S3C RTC Driver");
MODULE_AUTHOR("Ben Dooks <ben@simtec.co.uk>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:s3c2410-rtc");

里面的rtc_class_ops（就是字符驱动里file_operations的作用），完成了硬件的操作。如下：

static const struct rtc_class_ops s3c_rtcops = {
 .open  = s3c_rtc_open,
 .release = s3c_rtc_release,
 .read_time = s3c_rtc_gettime,
 .set_time = s3c_rtc_settime,
 .read_alarm = s3c_rtc_getalarm,
 .set_alarm = s3c_rtc_setalarm,
 .irq_set_freq = s3c_rtc_setfreq,
 .irq_set_state = s3c_rtc_setpie,
 .proc  = s3c_rtc_proc,
 .alarm_irq_enable = s3c_rtc_setaie,
};

　　再看probe函数，先从device里面获取资源，irq和mem，里面的函数以后慢慢再看啊！然后再使能rct，注册rtc_class_ops。后面是一些小操作。

　　这里的suspend和resume函数是电源管理的时候使用，这里先忽略。

　　remove函数，前面说了，就是字符设备里面的卸载，看看里面都有些什么吧。

platform_set_drvdata(dev, NULL);　　//将设备数据置0；
 rtc_device_unregister(rtc);　　　　//注销rtc设备

 s3c_rtc_setpie(&dev->dev, 0); 　　//停止硬件中断
 s3c_rtc_setaie(0);

 clk_disable(rtc_clk);　　　　//rtc的一些注销
 clk_put(rtc_clk);
 rtc_clk = NULL;

 iounmap(s3c_rtc_base);　　//释放内存空间
 release_resource(s3c_rtc_mem);
 kfree(s3c_rtc_mem);

注册和卸载的程序很简单。

static int __init s3c_rtc_init(void)
{
 printk(banner);
 return platform_driver_register(&s3c_rtc_driver);
}

static void __exit s3c_rtc_exit(void)
{
 platform_driver_unregister(&s3c_rtc_driver);
}

　　

至此，platform设备驱动粗略的讲述完毕。再次强调：它这样封装的好处，在设备和驱动分离，方便移植。当然，在同个平台，这样做很方便添加或删除外设驱动。 只需在板文件添加或注释掉就ok了。 

 ps：ioremap内核中的使用，往往是为某个设备预留一块内存，当使用的时候需要在board中定义这个设备的内存resource。通过 platform_get_resource获得设备的起始地址后，可以对其进行request_mem_region和ioremap等操作，以便应用程序对其进行操作。