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(intxtal) { 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：

structcpu_table { unsigned long idcode; unsigned long idmask; void (*map_io)(void); void (*init_uarts)(structs3c2410_uartcfg *cfg,int no); void (*init_clocks)(intxtal); int (*init)(void); const char*name; };

static structcpu_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(intxtal) { /* initialise the clocks here, to allow other things like the * console to use them, and to add new ones after the initialisation */ s3c24xx_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 longxtal) { 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); ints3c24xx_register_clock(structclk *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 longfclk, 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; }

s3c24xx_register_baseclocks(xtal); //完成祖宗级别时钟的注册

s3c244x_setup_clocks();//填充祖宗级别时钟结构，方便以后调用

s3c2410_baseclk_add();//添加一些外设时钟结构到list中，并且关闭它们方便省电

本篇文章来源于 Linux公社网站(www.linuxidc.com) 原文链接：http://www.linuxidc.com/Linux/2012-03/56418.htm