CLK（1）——fixed-clock

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最新推荐文章于 2024-11-30 15:28:24 发布

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分类专栏： Linux clk时钟文章标签： linux 运维

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本文详细介绍了Linux内核中固定时钟和固定分频因子时钟的概念，以及它们在设备节点如CAN节点中的配置。通过分析相关驱动函数，展示了如何初始化和使用这些时钟。同时，提供了相关驱动源代码，如`clk_osc24m`和`clk_pll_periph0x2`，展示了如何将pll时钟作为固定分频因子时钟的源。

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简析内核中固定时钟及相关时钟的定义和初始化：

参考链接：
https://blog.youkuaiyun.com/zgtzqzg2020/article/details/109220048
https://www.freesion.com/article/4436438726/

can节点中配置的24M的固定时钟：

clk_osc24m: osc24m {
	#clock-cells = <0>;
	compatible = "allwinner,fixed-clock";
	clock-frequency = <24000000>;
	clock-output-names = "osc24m";
};

can0: can@0 {
	compatible = "microchip,mcp2515";
	pinctrl-names = "default";
	clocks = <&clk_osc24m>;
	status = "okay";
};

相关文件：
linux-4.9/drivers/clk/sunxi/clk-sunxi.c
linux-4.9/drivers/clk/sunxi/clk-sun50iw9.c
linux-4.9/include/linux/clk-provider.h

pll-clock和fixed-factor-clock（固定分频因子时钟），可以看到clk_pll_periph0x2使用clk_pll_periph0作为其时钟源：

clk_pll_periph0: pll_periph0 {
                        #clock-cells = <0>;
                        compatible = "allwinner,pll-clock";
                        assigned-clocks = <&clk_pll_periph0>;
                        assigned-clock-rates = <600000000>;
                        lock-mode = "new";
                        clock-output-names = "pll_periph0";
                };

clk_pll_periph0x2: pll_periph0x2 {
                        #clock-cells = <0>;
                        compatible = "allwinner,fixed-factor-clock";
                        clocks = <&clk_pll_periph0>;
                        clock-mult = <2>;
                        clock-div = <1>;
                        clock-output-names = "pll_periph0x2";
                };

固定时钟驱动函数：
static void __init of_sunxi_fixed_clk_setup(struct device_node *node)
{
        struct clk *clk;
        const char *clk_name = node->name;
        u32 rate;

        if (of_property_read_u32(node, "clock-frequency", &rate))
                return;

        if (of_property_read_string(node, "clock-output-names", &clk_name)) {
                pr_err("%s:get clock-output-names failed in %s node\n",
                                                __func__, node->full_name);
                return;
        }

        clk = clk_register_fixed_rate(NULL, clk_name, NULL, CLK_IS_ROOT, rate);
        if (!IS_ERR(clk)) {
                clk_register_clkdev(clk, clk_name, NULL);
                of_clk_add_provider(node, of_clk_src_simple_get, clk);
        }
}

固定分频因子时钟驱动函数：
static void __init of_sunxi_fixed_factor_clk_setup(struct device_node *node)
{
        struct clk *clk;
        const char *clk_name = node->name;
        const char *parent_name;
        u32 div, mult;

        if (of_property_read_u32(node, "clock-div", &div)) {
                pr_err("%s Fixed factor clock <%s> must have a clock-div property\n",
                        __func__, node->name);
                return;
        }

        if (of_property_read_u32(node, "clock-mult", &mult)) {
                pr_err("%s Fixed factor clock <%s> must have a clokc-mult property\n",
                        __func__, node->name);
                return;
        }

        if (of_property_read_string(node, "clock-output-names", &clk_name)) {
                pr_err("%s:get clock-output-names failed in %s node\n",
                                                __func__, node->full_name);
                return;
        }
        parent_name = of_clk_get_parent_name(node, 0);

        clk = clk_register_fixed_factor(NULL, clk_name, parent_name, 0,
                                        mult, div);
        if (!IS_ERR(clk)) {
                clk_register_clkdev(clk, clk_name, NULL);
                of_clk_add_provider(node, of_clk_src_simple_get, clk);
        }
}

CLK_OF_DECLARE(sunxi_clocks_init, "allwinner,clk-init", of_sunxi_clocks_init);
CLK_OF_DECLARE(sunxi_fixed_clk, "allwinner,fixed-clock", of_sunxi_fixed_clk_setup);
CLK_OF_DECLARE(sunxi_pll_clk, "allwinner,pll-clock", of_sunxi_pll_clk_setup);
CLK_OF_DECLARE(sunxi_fixed_factor_clk, "allwinner,fixed-factor-clock", of_sunxi_fixed_factor_clk_setup);
CLK_OF_DECLARE(sunxi_cpu_clk, "allwinner,cpu-clock", of_sunxi_cpu_clk_setup);
CLK_OF_DECLARE(sunxi_periph_clk, "allwinner,periph-clock", of_sunxi_periph_clk_setup);
CLK_OF_DECLARE(periph_cpus_clk, "allwinner,periph-cpus-clock", of_sunxi_periph_cpus_clk_setup);

#define CLK_OF_DECLARE(name, compat, fn) OF_DECLARE_1(clk, name, compat, fn)

TBC