设备树中时钟的使用

s3c2440.dtsi

xti: xti_clock {
		compatible = "fixed-clock";
		clock-frequency = <12000000>;//晶振
		clock-output-names = "xti";
		#clock-cells = <0>;
	};

	clocks: clock-controller@4c000000 {
		compatible = "samsung,s3c2440-clock";
		reg = <0x4c000000 0x20>;//时钟控制寄存器
		#clock-cells = <1>;
	};

文档:
内核 Documentation/devicetree/bindings/clock/clock-bindings.txt
内核 Documentation/devicetree/bindings/clock/samsung,s3c2410-clock.txt

a. 设备树中定义了各种时钟, 在文档中称之为"Clock providers", 比如:
clocks: clock-controller@4c000000 {
compatible = “samsung,s3c2440-clock”;
reg = <0x4c000000 0x20>;
#clock-cells = <1>; // 想使用这个clocks时要提供1个u32来指定它, 比如选择这个clocks中发出的LCD时钟、PWM时钟
};

b. 设备需要时钟时, 它是"Clock consumers", 它描述了使用哪一个"Clock providers"中的哪一个时钟(id), 比如:
fb0: fb@4d000000{
compatible = “jz2440,lcd”;
reg = <0x4D000000 0x60>;
interrupts = <0 0 16 3>;
clocks = <&clocks HCLK_LCD>; // 使用clocks即clock-controller@4c000000中的HCLK_LCD
};

c. 驱动中获得/使能时钟:

	// 确定时钟个数
	int nr_pclks = of_count_phandle_with_args(dev->of_node, "clocks",
						"#clock-cells");
	// 获得时钟
	for (i = 0; i < nr_pclks; i++) {
		struct clk *clk = of_clk_get(dev->of_node, i);
	}
	// 使能时钟
	clk_prepare_enable(clk);
	// 禁止时钟
	clk_disable_unprepare(clk);