Linux内核时钟框架实例
Linux内核时钟框架实例
今天想自己写个adc的驱动，发现不清楚系统各个模块的系统时钟如何使用。总不能自己想怎么弄，就怎么弄吧，还是学学框架吧——使用时钟的框架。adc_clock = clk_get(NULL, "adc");
if (!adc_clock) {
printk(KERN_ERR "failed to get adc clock source\n");
return -ENOENT;
}
clk_use(adc_clock);
clk_enable(adc_clock);
上面的这段代码是touchscreen的驱动中的一段，我不清楚，所以去学学系统各个模块时钟的使用方式。在系统的初始化的时候，看见过，但是忘了，再回顾一下。 那是在paging_init()中调用了 mdesc->map_io()，
void __init sbc2440_map_io(void)
{
s3c24xx_init_io(sbc2440_iodesc, ARRAY_SIZE(sbc2440_iodesc));
s3c24xx_init_clocks(12000000); //这个是系统各个部分始终初始化的起点
s3c24xx_init_uarts(sbc2440_uartcfgs, ARRAY_SIZE(sbc2440_uartcfgs));
s3c24xx_set_board(&sbc2440_board);
s3c_device_nand.dev.platform_data = &bit_nand_info;
}
跟 cpu_table 有关，拷贝过来
/* table of supported CPUs */
static const char name_s3c2410[] = "S3C2410";
static const char name_s3c2440[] = "S3C2440";
static const char name_s3c2410a[] = "S3C2410A";
static const char name_s3c2440a[] = "S3C2440A";
static struct cpu_table cpu_ids[] __initdata =
{
{
.idcode = 0x32410000,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410_init,
.name = name_s3c2410
},
{
.idcode = 0x32410002,
.idmask = 0xffffffff,
.map_io = s3c2410_map_io,
.init_clocks = s3c2410_init_clocks,
.init_uarts = s3c2410_init_uarts,
.init = s3c2410_init,
.name = name_s3c2410a
},
{
.idcode = 0x32440000,
.idmask = 0xffffffff,
.map_io = s3c2440_map_io,
.init_clocks = s3c2440_init_clocks,
.init_uarts = s3c2440_init_uarts,
.init = s3c2440_init,
.name = name_s3c2440
},
{
.idcode = 0x32440001,
.idmask = 0xffffffff,
.map_io = s3c2440_map_io,
.init_clocks = s3c2440_init_clocks,
.init_uarts = s3c2440_init_uarts,
.init = s3c2440_init,
.name = name_s3c2440a
}
};
和时钟相关的调用路径： 在 s3c24xx_init_clocks() -> (cpu->init_clocks)(xtal)-> s3c24xx_setup_clocks()这个s3c24xx_setup_clocks()注册了系统的所有时钟，仔细看看它。 在这个函数被调用之前，代码已经根据3C2410_MPLLCON，S3C2410_CLKDIVN寄存器和晶振的频率计算出了fclk，hclk，pclk，他们应该分别是400M,100M，50M。
struct clk
{
struct list_head list;
struct module *owner;
struct clk *parent;
const char *name;
int id;
atomic_t used;
unsigned long rate;
unsigned long ctrlbit;
int (*enable)(struct clk *, int enable);
};
clk数据结构是系统中时钟的抽象，它用list串成一个双向链表，在这个clocks链表里的clk结构，说明是系统中已经注册的，parent表示他的来源，f,h,p之一，name是寻找到某个clk的唯一标识��enable是面向对象的思想的体现，不过，这里没有用到，只是全部被填充为 s3c24xx_clkcon_enable()。
/* clock information */
static LIST_HEAD(clocks);
static DECLARE_MUTEX(clocks_sem);
/* clock definitions */
static struct clk init_clocks[] =
{
{
.name = "nand",
.id = -1,
.parent = &clk_h,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_NAND
},
{
.name = "lcd",
.id = -1,
.parent = &clk_h,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_LCDC
},
{
.name = "usb-host",
.id = -1,
.parent = &clk_h,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_USBH
},
{
.name = "usb-device",
.id = -1,
/*.parent = &clk_h, */
.parent = &clk_xtal,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_USBD
},
{
.name = "timers",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_PWMT
},
{
.name = "sdi",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_SDI
},
{
.name = "uart",
.id = 0,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART0
},
{
.name = "uart",
.id = 1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART1
},
{
.name = "uart",
.id = 2,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_UART2
},
{
.name = "gpio",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_GPIO
},
{
.name = "rtc",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_RTC
},
{
.name = "adc",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_ADC
},
{
.name = "i2c",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_IIC
},
{
.name = "iis",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_IIS
},
{
.name = "spi",
.id = -1,
.parent = &clk_p,
.enable = s3c24xx_clkcon_enable,
.ctrlbit = S3C2410_CLKCON_SPI
},
{
.name = "watchdog",
.id = -1,
.parent = &clk_p,
.ctrlbit = 0
}
};
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