smdkv210_map_io

static void __init smdkv210_map_io(void)
{
    s5p_init_io(NULL, 0, S5P_VA_CHIPID);
    s3c24xx_init_clocks(24000000);
    s3c24xx_init_uarts(smdkv210_uartcfgs, ARRAY_SIZE(smdkv210_uartcfgs));
    s5p_set_timer_source(S5P_PWM2, S5P_PWM4);
}

void __init s5p_init_io(struct map_desc *mach_desc,
            int size, void __iomem *cpuid_addr)
{
    unsigned long idcode;

    /* initialize the io descriptors we need for initialization */
    iotable_init(s5p_iodesc, ARRAY_SIZE(s5p_iodesc));
    if (mach_desc)
        iotable_init(mach_desc, size);

    idcode = __raw_readl(cpuid_addr);
    s3c_init_cpu(idcode, cpu_ids, ARRAY_SIZE(cpu_ids));//从CPUids中查找开发板自己的cpu
}

void __init s3c_init_cpu(unsigned long idcode,
             struct cpu_table *cputab, unsigned int cputab_size)
{
    cpu = s3c_lookup_cpu(idcode, cputab, cputab_size);//在cputable中查询，查找的结果存放在cpu全局变量中

    if (cpu == NULL) {
        printk(KERN_ERR "Unknown CPU type 0x%08lx\n", idcode);
        panic("Unknown S3C24XX CPU");
    }

    printk("CPU %s (id 0x%08lx)\n", cpu->name, idcode);

    if (cpu->map_io == NULL || cpu->init == NULL) {
        printk(KERN_ERR "CPU %s support not enabled\n", cpu->name);
        panic("Unsupported Samsung CPU");
    }

    cpu->map_io(); //执行 如下
cpu_ids[] 中的s5pv210_map_io
}

static struct cpu_table cpu_ids[] __initdata = {
    {
        .idcode        = 0x56440100,
        .idmask        = 0xfffff000,
        .map_io        = s5p6440_map_io,
        .init_clocks    = s5p6440_init_clocks,
        .init_uarts    = s5p6440_init_uarts,
        .init        = s5p64x0_init,
        .name        = name_s5p6440,
    }, {
        .idcode        = 0x36450000,
        .idmask        = 0xfffff000,
        .map_io        = s5p6450_map_io,
        .init_clocks    = s5p6450_init_clocks,
        .init_uarts    = s5p6450_init_uarts,
        .init        = s5p64x0_init,
        .name        = name_s5p6450,
    }, {
        .idcode        = 0x43100000,
        .idmask        = 0xfffff000,
        .map_io        = s5pc100_map_io,
        .init_clocks    = s5pc100_init_clocks,
        .init_uarts    = s5pc100_init_uarts,
        .init        = s5pc100_init,
        .name        = name_s5pc100,
    }, {
        .idcode        = 0x43110000,
        .idmask        = 0xfffff000,
        .map_io        = s5pv210_map_io,
        .init_clocks    = s5pv210_init_clocks,
        .init_uarts    = s5pv210_init_uarts,
        .init        = s5pv210_init,
        .name        = name_s5pv210,
    }, {
        .idcode        = 0x43210000,
        .idmask        = 0xfffe0000,
        .map_io        = exynos4_map_io,
        .init_clocks    = exynos4_init_clocks,
        .init_uarts    = exynos4_init_uarts,
        .init        = exynos4_init,
        .name        = name_exynos4210,
    },
};

void __init s5pv210_map_io(void)
{
iotable_init(s5pv210_iodesc, ARRAY_SIZE(s5pv210_iodesc));

/* initialise device information early */
s5pv210_default_sdhci0();
s5pv210_default_sdhci1();
s5pv210_default_sdhci2();
s5pv210_default_sdhci3();

s3c_adc_setname("s3c64xx-adc");

s3c_cfcon_setname("s5pv210-pata");

s3c_fimc_setname(0, "s5pv210-fimc");
s3c_fimc_setname(1, "s5pv210-fimc");
s3c_fimc_setname(2, "s5pv210-fimc");

/* the i2c devices are directly compatible with s3c2440 */
s3c_i2c0_setname("s3c2440-i2c");
s3c_i2c1_setname("s3c2440-i2c");
s3c_i2c2_setname("s3c2440-i2c");

s3c_fb_setname("s5pv210-fb");

/* Use s5pv210-keypad instead of samsung-keypad */
samsung_keypad_setname("s5pv210-keypad");
}

完成s5p_init_io(NULL, 0, S5P_VA_CHIPID);后继续执行s3c24xx_init_clocks(24000000)如下所示

void __init s3c24xx_init_clocks(int xtal)
{
    if (xtal == 0)
        xtal = 12*1000*1000;

    if (cpu == NULL)
        panic("s3c24xx_init_clocks: no cpu setup?\n");

    if (cpu->init_clocks == NULL)
        panic("s3c24xx_init_clocks: cpu has no clock init\n");
    else
        (cpu->init_clocks)(xtal);  //由于在之前填充了cpu全局变量，实际就是执行
s5pv210_init_clocks （ .init_clocks    = s5pv210_init_clocks）
}

s5pv210_init_clocks如下：

void __init s5pv210_init_clocks(int xtal)
{
    printk(KERN_DEBUG "%s: initializing clocks\n", __func__);

    s3c24xx_register_baseclocks(xtal); //注册基本时钟,24XX
    s5p_register_clocks(xtal);  //都是注册时钟
    s5pv210_register_clocks();
//都是注册时钟
    s5pv210_setup_clocks();
}

int __init s3c24xx_register_baseclocks(unsigned long xtal)
{
    printk(KERN_INFO "S3C24XX Clocks, Copyright 2004 Simtec Electronics\n");

    clk_xtal.rate = xtal; // 设置
clk_xtal.rate时钟速率，clk_xtal是struct clk类型，这个clk类型包含了控制位和控制函数，还有一个链表头，能够和其他clk构成链表机构

    /* register our clocks */

    if (s3c24xx_register_clock(&clk_xtal) < 0)//注册
clk_xtal到链表中
        printk(KERN_ERR "failed to register master xtal\n");

    if (s3c24xx_register_clock(&clk_mpll) < 0)
//注册 
clk_mpll 到链表中
        printk(KERN_ERR "failed to register mpll clock\n");

    if (s3c24xx_register_clock(&clk_upll) < 0)
//注册 
clk_upll 到链表中
        printk(KERN_ERR "failed to register upll clock\n");

    if (s3c24xx_register_clock(&clk_f) < 0)
//注册 
clk_f 到链表中
        printk(KERN_ERR "failed to register cpu fclk\n");

    if (s3c24xx_register_clock(&clk_h) < 0)
//注册 
clk_h 到链表中
        printk(KERN_ERR "failed to register cpu hclk\n");

    if (s3c24xx_register_clock(&clk_p) < 0)
//注册 
clk_p 到链表中
        printk(KERN_ERR "failed to register cpu pclk\n");

    return 0;
}

int s3c24xx_register_clock(struct clk *clk)
{
    if (clk->enable == NULL)
        clk->enable = clk_null_enable;

    /* add to the list of available clocks */

    /* Quick check to see if this clock has already been registered. */
    BUG_ON(clk->list.prev != clk->list.next);

    spin_lock(&clocks_lock);  //操作链表时获得自旋锁
    list_add(&clk->list, &clocks);  //将本clk插入到以clocks为链表头的链表中
    spin_unlock(&clocks_lock);

    return 0;
}

struct clk {
    struct list_head      list;
    struct module        *owner;
    struct clk           *parent;
    const char           *name;
    int              id;
    int              usage;
    unsigned long         rate;
    unsigned long         ctrlbit;

    struct clk_ops        *ops;
    int            (*enable)(struct clk *, int enable);
#if defined(CONFIG_PM_DEBUG) && defined(CONFIG_DEBUG_FS)
    struct dentry        *dent;    /* For visible tree hierarchy */
#endif
};

static LIST_HEAD(clocks);

//include/linux/list.h中
#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
    struct list_head name = LIST_HEAD_INIT(name)

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}

通过上面，有了static LIST_HEAD(clocks)之后，其实就有一个clocks的list_head结构实体，其链表的next和prev 均指向了自己。

spinlock_t clocks_lock  //操作时钟链表对应的自旋锁