我对linux理解之alsa二
我们接着上一节：
static int wm8994_probe(struct platform_device *pdev)
{
    struct snd_soc_device *socdev = platform_get_drvdata(pdev);
    struct snd_soc_codec *codec = wm8994_codec;
    int ret = 0;

    socdev->card->codec = wm8994_codec;//已经在codec列表里

    /* register pcms */
    ret = snd_soc_new_pcms(socdev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1);//注册pcms，1
    if (ret < 0) {
        dev_err(codec->dev, "failed to create pcms\n");
        return ret;
    }
   
    snd_soc_add_controls(codec, wm8994_snd_controls,//添加控制，2
                 ARRAY_SIZE(wm8994_snd_controls));
    snd_soc_dapm_new_controls(codec, wm8994_dapm_widgets,//添加dapm的widgets，3
                  ARRAY_SIZE(wm8994_dapm_widgets));

    snd_soc_dapm_add_routes(codec, audio_map, ARRAY_SIZE(audio_map));//添加dapm的路径，4

//    wm8994_audio_start_dac(codec);
//    wm8994_audio_stop_speaker(codec);

    if (tda19989_get_status()) {
        wm8994_update_bit(codec, WM8994_POWER_MANAGEMENT_1,
                0, WM8994_SPKOUTR_ENA_MASK | WM8994_SPKOUTL_ENA_MASK);
        wm8994_update_bit(codec, WM8994_AIF1_DAC1_FILTERS_1,
                WM8994_AIF1DAC1_MUTE, WM8994_AIF1DAC1_MUTE);
        tda19989_pcm_mute((bool)1);
    }
    ret = snd_soc_init_card(socdev);//初始化card，5
    if (ret < 0) {
        printk(KERN_ERR "wm8994: failed to register card\n");
        snd_soc_free_pcms(socdev);
        snd_soc_dapm_free(socdev);
        return ret;
    }
   
    INIT_WORK(&wm8994_trigger_event, wm8994_do_trigger);

    return 0;
}

我们将分为上面标记的5部分进行分析。
1，snd_soc_new_pcms(socdev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1)：
int snd_soc_new_pcms(struct snd_soc_device *socdev, int idx, const char *xid)
{
    struct snd_soc_card *card = socdev->card;
    struct snd_soc_codec *codec = card->codec;
    int ret = 0, i;

    mutex_lock(&codec->mutex);
    /* register a sound card */
    ret = snd_card_create(idx, xid, codec->owner, 0, &codec->card);//注册一个声卡,其中将会有control的ops注册到card的devices里面,1-1
    if (ret < 0) {
        printk(KERN_ERR "asoc: can't create sound card for codec %s\n",
            codec->name);
        mutex_unlock(&codec->mutex);
        return -ENODEV;
    }

    codec->socdev = socdev;
    codec->card->dev = socdev->dev;
    codec->card->private_data = codec;
    strncpy(codec->card->driver, codec->name, sizeof(codec->card->driver));
    /* create the pcms */
    for (i = 0; i < card->num_links; i++) {//根据dai连接数目，决定创建多少个pcm
        ret = soc_new_pcm(socdev, &card->dai_link[i], i);//为每个card新建pcm流，1-2
        if (ret < 0) {