1. 数字mic驱动分析_数字mic clock

一般遇到的音频硬件都是这样的

由于项目不需要播放只需要录音，于是将模拟的mic换成了数字mic，直接通过i2s连接到soc

由于还要使用alsa架构进行录音，所以这里不能简单的写个代码读i2s数据，需要虚拟出一个codec

 上面就是我们这次要分析的数字mic驱动

ALSA架构中有machine，codec，platform的概率

这里可以简单的认为

codec这里就是数字mic

platform指rk的i2s以及dma

machine则是将上面2个关联起来

这3者的dts配置如下，注意这里基于rv1126平台，linux4.19.111

    digital_mic: digital-mic {
         status = "okay";
         compatible = "simple-audio-card";
         simple-audio-card,format = "i2s";
         simple-audio-card,mclk-fs = <256>;
         simple-audio-card,name = "digital-mic";
         simple-audio-card,cpu {
             sound-dai = <&i2s0_8ch>;
         };
 
         simple-audio-card,codec {
             sound-dai = <&dummy_codec>;
         };
    };
    
    i2s0_8ch: i2s@ff800000 {
        compatible = "rockchip,rv1126-i2s-tdm";
        reg = <0xff800000 0x1000>;
        interrupts = <GIC_SPI 46 IRQ_TYPE_LEVEL_HIGH>;
        clocks = <&cru MCLK_I2S0_TX>, <&cru MCLK_I2S0_RX>, <&cru HCLK_I2S0>;
        clock-names = "mclk_tx", "mclk_rx", "hclk";
        dmas = <&dmac 20>, <&dmac 19>;
        dma-names = "tx", "rx";
        resets = <&cru SRST_I2S0_TX_M>, <&cru SRST_I2S0_RX_M>;
        reset-names = "tx-m", "rx-m";
        rockchip,cru = <&cru>;
        rockchip,grf = <&grf>;
        pinctrl-names = "default";
        pinctrl-0 = <&i2s0m0_sclk_tx
                 &i2s0m0_sclk_rx
                 &i2s0m0_lrck_tx
                 &i2s0m0_lrck_rx
                 &i2s0m0_sdi0
                 &i2s0m0_sdo0
                 &i2s0m0_sdo1_sdi3
                 &i2s0m0_sdo2_sdi2
                 &i2s0m0_sdo3_sdi1>;
        status = "disabled";
    }; 
    
    &i2s0_8ch {
    	status = "okay";
    	#sound-dai-cells = <0>;
    	rockchip,clk-trcm = <0>;
    	rockchip,i2s-rx-route = <0 1 2 3>;
    	pinctrl-names = "default";
    	pinctrl-0 = <&i2s0m0_lrck_rx
        		&i2s0m0_sclk_rx
        		&i2s0m0_sdi0>;
    	rockchip,capture-only;
    }; 
    
    dummy_codec: dummy-codec {
        compatible = "rockchip,dummy-codec";
        #sound-dai-cells = <0>;
    };