clk_get函数实现，Linux内核时钟框架

http://blog.csdn.net/shushi0123/article/details/7318816

（1） 对应外设时钟的开启

struct clk=clk_get(NULL,"adc");

clk.enable();

之后adc对应的时钟位就能时能。

struct clk *clk_get(struct device *dev, const char *id)
{
..........
list_for_each_entry(p, &clocks, list) {
if (p->id == idno &&
strcmp(id, p->name) == 0 &&
try_module_get(p->owner)) {
clk = p;
break;
}
}

.............................................
return clk;
}

clk_get从一个时钟list链表中以字符id名称来查找一个时钟clk结构体并且返回，最后调用clk.enable()，来时能对应的外设时钟源。

（2） list的设置和对应list中的成员。

MACHINE_START(MINI2440, "FriendlyARM Mini2440 development board")
.phys_io = S3C2410_PA_UART,
.io_pg_offst = (((u32)S3C24XX_VA_UART) >> 18) & 0xfffc,
.boot_params = S3C2410_SDRAM_PA + 0x100,

.init_irq = s3c24xx_init_irq,
.map_io = mini2440_map_io,
.init_machine = mini2440_machine_init,
.timer = &s3c24xx_timer,
MACHINE_END

static void __init mini2440_map_io(void)
{
s3c24xx_init_io(mini2440_iodesc, ARRAY_SIZE(mini2440_iodesc));
s3c24xx_init_clocks(12000000);
s3c24xx_init_uarts(mini2440_uartcfgs, ARRAY_SIZE(mini2440_uartcfgs));
}

void __init s3c24xx_init_io(struct map_desc *mach_desc, int size)
{
unsigned long idcode = 0x0;
...........
arm_pm_restart = s3c24xx_pm_restart;

s3c_init_cpu(idcode, cpu_ids, ARRAY_SIZE(cpu_ids));
}

void __init s3c_init_cpu(unsigned long idcode,
struct cpu_table *cputab, unsigned int cputab_size)
{
cpu = s3c_lookup_cpu(idcode, cputab, cputab_size);
......
cpu->map_io();

static struct cpu_table cpu_ids[] __initdata = {
.......
{
.idcode = 0x32410002,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410a_init,
.name = name_s3c2410a
},
.......
}

在static void __init mini2440_map_io(void)中调用s3c24xx_init_io(mini2440_iodesc, ARRAY_SIZE(mini2440_iodesc))后返回了struct cpu_table cpu_ids中的

{
.idcode = 0x32410002,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410a_init,
.name = name_s3c2410a
}

cpu_table

之后运行s3c24xx_init_clocks(12000000)后又执行(cpu->init_clocks)(xtal)，对应就是s3c2410_init_clocks

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
*/

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
}

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;
}

以上的作用就是将一个个的时钟结构体链接成双向链表的，以后好使用clk_get在时钟结构体链表中查找id字符匹配的clk结构体并返回。

s3c2410_baseclk_add()

{

..........

clkp = init_clocks_disable;
for (ptr = 0; ptr < ARRAY_SIZE(init_clocks_disable); ptr++, clkp++) {

ret = s3c24xx_register_clock(clkp);
if (ret < 0) {
printk(KERN_ERR "Failed to register clock %s (%d)\n",
clkp->name, ret);
}

s3c2410_clkcon_enable(clkp, 0);
}

........

}

s3c2410_baseclk_add()添加其他外设的clk结构

clk.enable()，最后调用的

static struct clk init_clocks_disable[] = {

......

{
.name = "adc",
.id = -1,
.parent = &clk_p,
.enable = s3c2410_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_ADC,

}

......

}中的

int s3c2410_clkcon_enable(struct clk *clk, int enable)
{
unsigned int clocks = clk->ctrlbit;
unsigned long clkcon;

clkcon = __raw_readl(S3C2410_CLKCON);

if (enable)
clkcon |= clocks;
else
clkcon &= ~clocks;

/* ensure none of the special function bits set */
clkcon &= ~(S3C2410_CLKCON_IDLE|S3C2410_CLKCON_POWER);

__raw_writel(clkcon, S3C2410_CLKCON);

return 0;
}其根据.ctrlbit = S3C2410_CLKCON_ADC,来使能对应ADC时钟。

至此完毕。