ARM-Linux时钟初始化

ARM-Linux时钟初始化

 

ARM-linux时钟初始化是从MACHINE_START中的map_io函数开始的，map_io函数中会调用s3c24xx_init_clocks(12000000);来进行，我们来看一下初始化过程

static struct cpu_table *cpu;

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);

}

示例如下：

struct cpu_table {

    unsigned long idcode;

    unsigned long idmask;

    void       (*map_io)(void);

    void       (*init_uarts)(struct s3c2410_uartcfg *cfg, int no);

    void       (*init_clocks)(int xtal);

    int    (*init)(void);

    const char *name;

};

 

static struct cpu_table cpu_ids[] __initdata = {

    //……

    {

       .idcode       = 0x32440000,

       .idmask       = 0xffffffff,

       .map_io       = s3c244x_map_io,

       .init_clocks  = s3c244x_init_clocks,

       .init_uarts   = s3c244x_init_uarts,

       .init      = s3c2440_init,

       .name      = name_s3c2440

    },

    {

       .idcode       = 0x32440001,

       .idmask       = 0xffffffff,

       .map_io       = s3c244x_map_io,

       .init_clocks  = s3c244x_init_clocks,

       .init_uarts   = s3c244x_init_uarts,

       .init      = s3c2440_init,

       .name      = name_s3c2440a

    },

    {

       .idcode       = 0x32440aaa,

       .idmask       = 0xffffffff,

       .map_io       = s3c244x_map_io,

       .init_clocks  = s3c244x_init_clocks,

       .init_uarts   = s3c244x_init_uarts,

       .init      = s3c2442_init,

       .name      = name_s3c2442

    },

    {

       .idcode       = 0x32440aab,

       .idmask       = 0xffffffff,

       .map_io       = s3c244x_map_io,

       .init_clocks  = s3c244x_init_clocks,

       .init_uarts   = s3c244x_init_uarts,

       .init      = s3c2442_init,

       .name      = name_s3c2442b

    },

    //……

};

 

void __init s3c244x_init_clocks(int xtal)

{

    /* initialise the clocks here, to allow other things like the

     * console to use them, and to add new ones after the initialisation

     */

    register_baseclocks(xtal);

    s3c244x_setup_clocks();

    s3c2410_baseclk_add();

}

s3c24xx_register_baseclocks函数会向系统注册基本时钟，S3C2440A时钟链路：由外晶振OSC（或外部时钟）提供时钟输入，然后分成两路，一路由MPLL锁相环倍频出时钟FCK（核时钟），然后经分频出两路时钟HCLK（AHB总线外设时钟）和PCLK（APB总线外设时钟），另一路由UPLL锁相环倍频出时钟UCLK，为USB外设提供时钟，以下基本时钟中，xtal为外部晶振时钟，clk_mpll为经过MPLL锁相环倍频出时钟，clk_upll为由UPLL锁相环倍频出时钟UCLK，clk_f为内核时钟，即主频，clk_h为HCLK（AHB总线外设时钟）clk_p为PCLK（APB总线外设时钟）

int __init s3c24xx_register_baseclocks(unsigned long xtal)

{

    printk(KERN_INFO "S3C24XX Clocks, (c) 2004 Simtec Electronics\n");

    clk_xtal.rate = xtal;

 

    /* register our clocks */

 

    if (s3c24xx_register_clock(&clk_xtal) < 0)

       printk(KERN_ERR "failed to register master xtal\n");

 

    if (s3c24xx_register_clock(&clk_mpll) < 0)

       printk(KERN_ERR "failed to register mpll clock\n");

 

    if (s3c24xx_register_clock(&clk_upll) < 0)

       printk(KERN_ERR "failed to register upll clock\n");

 

    if (s3c24xx_register_clock(&clk_f) < 0)

       printk(KERN_ERR "failed to register cpu fclk\n");

 

    if (s3c24xx_register_clock(&clk_h) < 0)

       printk(KERN_ERR "failed to register cpu hclk\n");

 

    if (s3c24xx_register_clock(&clk_p) < 0)

       printk(KERN_ERR "failed to register cpu pclk\n");

 

    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;

 

    int        (*enable)(struct clk *, int enable);

    int        (*set_rate)(struct clk *c, unsigned long rate);

    unsigned long     (*get_rate)(struct clk *c);

    unsigned long     (*round_rate)(struct clk *c, unsigned long rate);

    int        (*set_parent)(struct clk *c, struct clk *parent);

};

clock.c文件定义一个list_head的链表，s3c24xx_register_clock函数会将clk结

构体的变量加入到这个链表中，函数定义如下

static LIST_HEAD(clocks);

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);

    list_add(&clk->list, &clocks);

    spin_unlock(&clocks_lock);

 

    return 0;

}

各主时钟的定义如下：

struct clk clk_xtal = {

    .name      = "xtal",

    .id    = -1,

    .rate      = 0,

    .parent       = NULL,

    .ctrlbit   = 0,

};

 

struct clk clk_ext = {

    .name      = "ext",

    .id    = -1,

};

 

struct clk clk_epll = {

    .name      = "epll",

    .id    = -1,

};

 

struct clk clk_mpll = {

    .name      = "mpll",

    .id    = -1,

    .set_rate  = clk_default_setrate,

};

 

struct clk clk_upll = {

    .name      = "upll",

    .id    = -1,

    .parent       = NULL,

    .ctrlbit   = 0,

};

 

struct clk clk_f = {

    .name      = "fclk",

    .id    = -1,

    .rate      = 0,

    .parent       = &clk_mpll,

    .ctrlbit   = 0,

    .set_rate  = clk_default_setrate,

};

 

struct clk clk_h = {

    .name      = "hclk",

    .id    = -1,

    .rate      = 0,

    .parent       = NULL,

    .ctrlbit   = 0,

    .set_rate  = clk_default_setrate,

};

 

struct clk clk_p = {

    .name      = "pclk",

    .id    = -1,

    .rate      = 0,

    .parent       = NULL,

    .ctrlbit   = 0,

    .set_rate  = clk_default_setrate,

};

 

struct clk clk_usb_bus = {

    .name      = "usb-bus",

    .id    = -1,

    .rate      = 0,

    .parent       = &clk_upll,

};

 

 

 

struct clk s3c24xx_uclk = {

    .name      = "uclk",

    .id    = -1,

};

 

时钟注册进系统后便可以通过，内核的API来操作时钟了，struct clk *clk_get(struct device *dev, const char *id)函数来获取一个名为Id的clk结构体指针，然后可以通过clk_get_rate来获取该时钟的频率，

如:printk(KERN_DEBUG ”fclk=%d \n”,clk_get_rate(clk_get(NULL,”fclk”)));

s3c244x_setup_clocks(void)会设置系统的基本时钟

void __init_or_cpufreq s3c244x_setup_clocks(void)

{

    struct clk *xtal_clk;

    unsigned long clkdiv;

    unsigned long camdiv;

    unsigned long xtal;

    unsigned long hclk, fclk, pclk;

    int hdiv = 1;

 

    xtal_clk = clk_get(NULL, "xtal");

    xtal = clk_get_rate(xtal_clk);

    clk_put(xtal_clk);

 

    fclk = s3c24xx_get_pll(__raw_readl(S3C2410_MPLLCON), xtal) * 2;

 

    clkdiv = __raw_readl(S3C2410_CLKDIVN);

    camdiv = __raw_readl(S3C2440_CAMDIVN);

 

    /* work out clock scalings */

 

    switch (clkdiv & S3C2440_CLKDIVN_HDIVN_MASK) {

    case S3C2440_CLKDIVN_HDIVN_1:

       hdiv = 1;

       break;

 

    case S3C2440_CLKDIVN_HDIVN_2:

       hdiv = 2;

       break;

 

    case S3C2440_CLKDIVN_HDIVN_4_8:

       hdiv = (camdiv & S3C2440_CAMDIVN_HCLK4_HALF) ? 8 : 4;

       break;

 

    case S3C2440_CLKDIVN_HDIVN_3_6:

       hdiv = (camdiv & S3C2440_CAMDIVN_HCLK3_HALF) ? 6 : 3;

       break;

    }

 

    hclk = fclk / hdiv;

    pclk = hclk / ((clkdiv & S3C2440_CLKDIVN_PDIVN) ? 2 : 1);

 

    /* print brief summary of clocks, etc */

 

    printk("S3C244X: core %ld.%03ld MHz, memory %ld.%03ld MHz, peripheral %ld.%03ld MHz\n",

           print_mhz(fclk), print_mhz(hclk), print_mhz(pclk));

 

    s3c24xx_setup_clocks(fclk, hclk, pclk);

}

 

s3c24xx_setup_clocks(fclk, hclk, pclk);它向链表中的相关变量赋值，定义如下：

void __init_or_cpufreq s3c24xx_setup_clocks(unsigned long fclk,

                     unsigned long hclk,

                     unsigned long pclk)

{

    clk_upll.rate = s3c24xx_get_pll(__raw_readl(S3C2410_UPLLCON),

                  clk_xtal.rate);

 

    clk_mpll.rate = fclk;

    clk_h.rate = hclk;

    clk_p.rate = pclk;

    clk_f.rate = fclk;

}