I2C子系統之I2C總線時鐘頻率設置

時鐘相關基本知識可先參考這篇http://www.linuxidc.com/Linux/2012-02/54968.htm

下面直接從總線時鐘初始化函數開始分析：

1. void __init s3c244x_init_clocks(int xtal)
2. {
3. /* initialise the clocks here, to allow other things like the
4. * console to use them, and to add new ones after the initialisation
5. */
7. s3c24xx_register_baseclocks(xtal);
8. s3c244x_setup_clocks();
9. s3c2410_baseclk_add();
10. }

s3c24xx_init_clocks主要實現兩個功能：

1.初始化s3c2440的總線時鐘。通過s3c24xx_register_baseclocks(xtal)和s3c244x_setup_clocks實現

2.想系統注冊外設時鐘。通過s3c2410_baseclk_add()實現

首先分析初始化系統時鐘

1. int __init s3c24xx_register_baseclocks(unsigned long xtal)
2. {
3. printk(KERN_INFO "S3C24XX Clocks, Copyright 2004 Simtec Electronics\n");
5. clk_xtal.rate = xtal;
7. /* register our clocks */
9. if (s3c24xx_register_clock(&clk_xtal) < 0)
10. printk(KERN_ERR "failed to register master xtal\n");
12. if (s3c24xx_register_clock(&clk_mpll) < 0)
13. printk(KERN_ERR "failed to register mpll clock\n");
15. if (s3c24xx_register_clock(&clk_upll) < 0)
16. printk(KERN_ERR "failed to register upll clock\n");
18. if (s3c24xx_register_clock(&clk_f) < 0)
19. printk(KERN_ERR "failed to register cpu fclk\n");
21. if (s3c24xx_register_clock(&clk_h) < 0)
22. printk(KERN_ERR "failed to register cpu hclk\n");
24. if (s3c24xx_register_clock(&clk_p) < 0)
25. printk(KERN_ERR "failed to register cpu pclk\n");
27. return 0;
28. }

依次向注冊clk_xtal、clk_mpll、clk_upll... ...clk_p等時鐘，clk_p等的定義如下：

1. struct clk clk_p = {
2. .name = "pclk",
3. .id = -1,
4. .rate = 0,
5. .parent = NULL,
6. .ctrlbit = 0,
7. .ops = &clk_ops_def_setrate,
8. };

注冊成功後然後通過s3c244x_setup_clocks->s3c24xx_setup_clocks(fclk, hclk, pclk)來初始化前面注冊的各個時鐘。

1. void __init_or_cpufreq s3c24xx_setup_clocks(unsigned long fclk,
2. unsigned long hclk,
3. unsigned long pclk)
4. {
5. clk_upll.rate = s3c24xx_get_pll(__raw_readl(S3C2410_UPLLCON),
6. clk_xtal.rate);
8. clk_mpll.rate = fclk;
9. clk_h.rate = hclk;
10. clk_p.rate = pclk;
11. clk_f.rate = fclk;
12. }