linux-kernel - 如何在 linux 内核设备树中定义时钟多路复用器

Question

我正在编写一个 linux 设备驱动程序，需要在设备树文件中定义以下时钟树:

注意:通过将 gpio 输出拉高或拉低来选择多路复用器中的振荡器。时钟发生器通过 I2C 编程。

这是我目前所拥有的示例:

clocks {
    /* fixed clock oscillators */
    osc22: oscillator22 {
        compatible = "fixed-clock";
        #clock-cells = <0>;
        clock-frequency = <22579200>;
    };

    osc24: oscillator24 {
        compatible = "fixed-clock";
        #clock-cells = <0>;
        clock-frequency = <24576000>;
    };

    /* clock multiplexer
     * I'm afraid the following is not going to work :( ?
     */
    mux: multiplexer {
        compatible = "mux-clock";     /* <-------- ??? */
        clocks = <&osc22>, <&osc24>;  /* parent clocks */
    };
};

i2c1 {
    /* clock generator */
    si5351: si5351c@60 {
        #address-cells = <1>;
        #size-cells = <0>;
        #clock-cells = <1>;
        compatible = "silabs,si5351c";
        reg = <0x60>;
        clocks = <0>, <&mux>;
        clock-names = "xtal", "clkin";
        status = "okay";

        clkout0 {
            reg = <0>;
            silabs,disable-state = <2>;
            silabs,clock-source = <3>;
        };
    };
};

引用:

• Clock Bindings
• Binding for simple fixed-rate clock sources
• Binding for Silicon Labs Si5351a/b/c programmable i2c clock generator

如何在设备树中定义一个简单的gpio 控制 时钟多路复用器？

Answer 1

正如@h3n 正确指出的那样，在提出这个问题时，内核并未提供对 gpio 控制的时钟多路复用器的支持。因此，我必须为此类设备添加通用时钟驱动程序。

此驱动程序 ( drivers/clk/clk-gpio.c ) 自 4.3-rc1 以来已在主线中。

上述用例的设备树绑定(bind)可能如下所示:

clocks {
    /* fixed clock oscillators */
    osc22: oscillator22 {
        compatible = "fixed-clock";
        #clock-cells = <0>;
        clock-frequency = <22579200>;
    };

    osc24: oscillator24 {
        compatible = "fixed-clock";
        #clock-cells = <0>;
        clock-frequency = <24576000>;
    };

    /* gpio-controlled clock multiplexer */
    mux: multiplexer {
        compatible = "gpio-mux-clock";
        clocks = <&osc22>, <&osc24>;  /* parent clocks */
        #clock-cells = <0>;
        select-gpios = <&gpio 42 GPIO_ACTIVE_HIGH>;
    };
};