Introduction

Concepts

DAI

DAI is a Digital Audio Interface. So a I2S on the Soc is a DAI and a Codec is a DAI. There are drivers for I2S. While there are seperate driver for those codecs. So how those DAIs are bound together to form a complete sound card device for upper layer?

It is very similar with MIPI driver where thers is a host driver and panel driver. The I2S driver is in the same postion of Host Driver while Codec driver is of panel driver.

How these two drivers are bound together

The “simple-audio-card” driver will associate the two DAI together:

 rk809_sound: rk809-sound {
     compatible = "simple-audio-card";
     simple-audio-card,format = "i2s";
     simple-audio-card,name = "rockchip,rk809-codec";
     simple-audio-card,mclk-fs = <256>;
     simple-audio-card,widgets =
         "Microphone", "Mic Jack",
         "Headphone", "Headphone Jack";
     simple-audio-card,routing =
         "Mic Jack", "MICBIAS1",
         "IN1P", "Mic Jack",
         "Headphone Jack", "HPOL",
         "Headphone Jack", "HPOR";
     simple-audio-card,cpu {
         sound-dai = <&i2s0_8ch>;
     };
     simple-audio-card,codec {
         sound-dai = <&rk809_codec>;
     };
 };

So this sound card contains (logically) two DAI:

the cpu dai “i2s0_8ch” and “rk809_codec” the external codec.

During sound card startup, the cpu dai’s clock is firstly enabled.

static int asoc_simple_card_startup(struct snd_pcm_substream *substream)
{
    struct snd_soc_pcm_runtime *rtd = substream->private_data;
    struct simple_card_data *priv = snd_soc_card_get_drvdata(rtd->card);
    struct simple_dai_props *dai_props =
        simple_priv_to_props(priv, rtd->num);
    int ret;

    ret = asoc_simple_card_clk_enable(&dai_props->cpu_dai);
    if (ret)
        return ret;

    ret = asoc_simple_card_clk_enable(&dai_props->codec_dai);
    if (ret)
        asoc_simple_card_clk_disable(&dai_props->cpu_dai);

    return ret;
}

The cpu dai’s clock is set via DTS. clocks and clock-names are used.

 i2s0_8ch: i2s@ff800000 {
     compatible = "rockchip,rv1126-i2s-tdm";
...
     clocks = <&cru MCLK_I2S0_TX>, <&cru MCLK_I2S0_RX>, <&cru HCLK_I2S0>;
     clock-names = "mclk_tx", "mclk_rx", "hclk";
...
 };

rockchip_i2s_hw_params