Linux-CCF-Provider

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介绍时钟提供者，首先要介绍设备树中与时钟节点相关内容，在设备树中描述时钟节点，有两种方式，第一种方式是将系统所有时钟抽象为一个虚拟设备，用一个节点表示

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clock: clock-controller@0x10030000 {
    compatible = "samsung,exynos4210-clock";
    reg = <0x10030000 0x20000>;
    #clock-cells = <1>;
};

clock-controller是这个时钟的名称，消费者在设备树中可以通过这个名称来引用该时钟。clock-cells值为1表示该时钟有多个输出，消费者通过ID值来指定要使用的时钟线

另一种方式是每个可输出的时钟都是一个独立的节点

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clocks {
    #address-cells = <1>;
    #size-cells = <1>;
    ranges;

    dummy: dummy {
        #clock-cells = <0>;
        compatible = "fixed-clock";
        clock-frequency = <0>;
    };

    osc24M: osc24M@01c20050 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-osc-clk";
        reg = <0x01c20050 0x4>;
        clock-frequency = <24000000>;
    };

    osc32k: osc32k {
        #clock-cells = <0>;
        compatible = "fixed-clock";
        clock-frequency = <32768>;
    };

    pll1: pll1@01c20000 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-pll1-clk";
        reg = <0x01c20000 0x4>;
        clocks = <&osc24M>;
    };

    cpu: cpu@01c20054 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-cpu-clk";
        reg = <0x01c20054 0x4>;
        clocks = <&osc32k>, <&osc24M>, <&pll1>, <&dummy>;
    };

    axi: axi@01c20054 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-axi-clk";
        reg = <0x01c20054 0x4>;
        clocks = <&cpu>;
    };

    axi_gates: axi_gates@01c2005c {
        #clock-cells = <1>;
        compatible = "allwinner,sun4i-axi-gates-clk";
        reg = <0x01c2005c 0x4>;
        clocks = <&axi>;
        clock-output-names = "axi_dram";
    };

    ahb: ahb@01c20054 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-ahb-clk";
        reg = <0x01c20054 0x4>;
        clocks = <&axi>;
    };

    ahb_gates: ahb_gates@01c20060 {
        #clock-cells = <1>;
        compatible = "allwinner,sun4i-ahb-gates-clk";
        reg = <0x01c20060 0x8>;
        clocks = <&ahb>;
        clock-output-names = "ahb_usb0", "ahb_ehci0",
             "ahb_ohci0", "ahb_ehci1", "ahb_ohci1", "ahb_ss",
             "ahb_dma", "ahb_bist", "ahb_mmc0", "ahb_mmc1",
             "ahb_mmc2", "ahb_mmc3", "ahb_ms", "ahb_nand",
             "ahb_sdram", "ahb_ace",    "ahb_emac", "ahb_ts",
             "ahb_spi0", "ahb_spi1", "ahb_spi2", "ahb_spi3",
             "ahb_pata", "ahb_sata", "ahb_gps", "ahb_ve",
             "ahb_tvd", "ahb_tve0", "ahb_tve1", "ahb_lcd0",
             "ahb_lcd1", "ahb_csi0", "ahb_csi1", "ahb_hdmi",
             "ahb_de_be0", "ahb_de_be1", "ahb_de_fe0",
             "ahb_de_fe1", "ahb_mp", "ahb_mali400";
    };

    apb0: apb0@01c20054 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-apb0-clk";
        reg = <0x01c20054 0x4>;
        clocks = <&ahb>;
    };

    apb0_gates: apb0_gates@01c20068 {
        #clock-cells = <1>;
        compatible = "allwinner,sun4i-apb0-gates-clk";
        reg = <0x01c20068 0x4>;
        clocks = <&apb0>;
        clock-output-names = "apb0_codec", "apb0_spdif",
            "apb0_ac97", "apb0_iis", "apb0_pio", "apb0_ir0",
            "apb0_ir1", "apb0_keypad";
    };

    /* dummy is pll62 */
    apb1_mux: apb1_mux@01c20058 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-apb1-mux-clk";
        reg = <0x01c20058 0x4>;
        clocks = <&osc24M>, <&dummy>, <&osc32k>;
    };

    apb1: apb1@01c20058 {
        #clock-cells = <0>;
        compatible = "allwinner,sun4i-apb1-clk";
        reg = <0x01c20058 0x4>;
        clocks = <&apb1_mux>;
    };

    apb1_gates: apb1_gates@01c2006c {
        #clock-cells = <1>;
        compatible = "allwinner,sun4i-apb1-gates-clk";
        reg = <0x01c2006c 0x4>;
        clocks = <&apb1>;
        clock-output-names = "apb1_i2c0", "apb1_i2c1",
            "apb1_i2c2", "apb1_can", "apb1_scr",
            "apb1_ps20", "apb1_ps21", "apb1_uart0",
            "apb1_uart1", "apb1_uart2", "apb1_uart3",
            "apb1_uart4", "apb1_uart5", "apb1_uart6",
            "apb1_uart7";
    };
};

osc24M和osc32k是两个时钟的根节点，它们的clock-cells均为0，直接使用节点的名字引用即可。pll1以osc24M作为时钟源，并提供时钟。ahb_gates的时钟来自ahb，并通过clock-output-names为多个输出定义了名称