codec音频编解码器驱动分析

之前在公司做过cs42l52编解码器的驱动，不过现在已然已经忘记了。目前手中有友善之臂的一款三星4412的开发板，那么就分析这款产品的音频编解码器吧。

如图所示，可以看出该开发板使用的是WM8960的音频编解码器，查找源码android-5.0.2/linux-3.0.86/sound/soc/codecs/wm8960.c存在，查看mach-tiny4412.c可以看到如下图

很显然可以看到wm8960音频编解码器的i2c地址是0x1a,其I2C连线如下图

也就是该设备还是一个i2c设备，现在来看它的代码
模块入口：

module_init(wm8960_modinit);

初始化函数：

static int __init wm8960_modinit(void)
{
    int ret = 0;
#if defined(CONFIG_I2C) || defined(CONFIG_I2C_MODULE)
    ret = i2c_add_driver(&wm8960_i2c_driver);
    if (ret != 0) {
        printk(KERN_ERR "Failed to register WM8960 I2C driver: %d\n",
               ret);
    }
#endif
    return ret;
}

对应的wm8960_i2c_driver数据

static struct i2c_driver wm8960_i2c_driver = {
    .driver = {
        .name = "wm8960-codec",
        .owner = THIS_MODULE,
    },
    .probe =    wm8960_i2c_probe,
    .remove =   __devexit_p(wm8960_i2c_remove),
    .id_table = wm8960_i2c_id,
};

一旦探测到设备执行wm8960_i2c_probe函数

static __devinit int wm8960_i2c_probe(struct i2c_client *i2c,
                      const struct i2c_device_id *id)
{
    struct wm8960_priv *wm8960;
    int ret;

    wm8960 = kzalloc(sizeof(struct wm8960_priv), GFP_KERNEL);
    if (wm8960 == NULL)
        return -ENOMEM;

    i2c_set_clientdata(i2c, wm8960);
    wm8960->control_type = SND_SOC_I2C;
    wm8960->control_data = i2c;

    ret = snd_soc_register_codec(&i2c->dev,
            &soc_codec_dev_wm8960, &wm8960_dai, 1);
    if (ret < 0)
        kfree(wm8960);
    return ret;
}

显然最重要的是snd_soc_register_codec(&i2c->dev,
&soc_codec_dev_wm8960, &wm8960_dai, 1);这一句了

static struct snd_soc_codec_driver soc_codec_dev_wm8960 = {
    .probe =    wm8960_probe,
    .remove =   wm8960_remove,
    .suspend =  wm8960_suspend,
    .resume =   wm8960_resume,
    .set_bias_level = wm8960_set_bias_level,
    .reg_cache_size = ARRAY_SIZE(wm8960_reg),
    .reg_word_size = sizeof(u16),
    .reg_cache_default = wm8960_reg,
};


static int wm8960_probe(struct snd_soc_codec *codec)
{
    struct wm8960_priv *wm8960 = snd_soc_codec_get_drvdata(codec);
    struct wm8960_data *pdata = dev_get_platdata(codec->dev);
    int ret;
    u16 reg;

    wm8960->set_bias_level = wm8960_set_bias_level_out3;
    codec->control_data = wm8960->control_data;

    if (!pdata) {
        dev_warn(codec->dev, "No platform data supplied\n");
    } else {
        if (pdata->dres > WM8960_DRES_MAX) {
            dev_err(codec->dev, "Invalid DRES: %d\n", pdata->dres);
            pdata->dres = 0;
        }

        if (pdata->capless)
            wm8960->set_bias_level = wm8960_set_bias_level_capless;
    }

    ret = snd_soc_codec_set_cache_io(codec, 7, 9, wm8960->control_type);
    if (ret < 0) {
        dev_err(codec->dev, "Failed to set cache I/O: %d\n", ret);
        return ret;
    }

    ret = wm8960_reset(codec);
    if (ret < 0) {
        dev_err(codec->dev, "Failed to issue reset\n");
        return ret;
    }

    wm8960->set_bias_level(codec, SND_SOC_BIAS_STANDBY);

    /* Latch the update bits */
    reg = snd_soc_read(codec, WM8960_LINVOL);
    snd_soc_write(codec, WM8960_LINVOL, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_RINVOL);
    snd_soc_write(codec, WM8960_RINVOL, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_LADC);
    snd_soc_write(codec, WM8960_LADC, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_RADC);
    snd_soc_write(codec, WM8960_RADC, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_LDAC);
    snd_soc_write(codec, WM8960_LDAC, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_RDAC);
    snd_soc_write(codec, WM8960_RDAC, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_LOUT1);
    snd_soc_write(codec, WM8960_LOUT1, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_ROUT1);
    snd_soc_write(codec, WM8960_ROUT1, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_LOUT2);
    snd_soc_write(codec, WM8960_LOUT2, reg | 0x100);
    reg = snd_soc_read(codec, WM8960_ROUT2);
    snd_soc_write(codec, WM8960_ROUT2, reg | 0x100);

    snd_soc_add_controls(codec, wm8960_snd_controls,
                     ARRAY_SIZE(wm8960_snd_controls));
    wm8960_add_widgets(codec);

    return 0;
}

在wm8960_probe这个函数中，我们可以看到一些写寄存器的操作，这个就是对应的wm8960设备的初始值，具体寄存器设置来哪些初始值得结合datasheet来分析，之前公司弄的cs42l52也是这样的，当时为了调节从codec出来的音量大小，就是修改这个位置的参数来解决的。

static struct snd_soc_dai_driver wm8960_dai = {
    .name = "wm8960-hifi",
    .playback = {
        .stream_name = "Playback",
        .channels_min = 1,
        .channels_max = 2,
        .rates = WM8960_RATES,
        .formats = WM8960_FORMATS,},
    .capture = {
        .stream_name = "Capture",
        .channels_min = 1,
        .channels_max = 2,
        .rates = WM8960_RATES,
        .formats = WM8960_FORMATS,},
    .ops = &wm8960_dai_ops,
    .symmetric_rates = 1,
};

static struct snd_soc_dai_ops wm8960_dai_ops = {
    .hw_params = wm8960_hw_params,
    .digital_mute = wm8960_mute,
    .set_fmt = wm8960_set_dai_fmt,
    .set_clkdiv = wm8960_set_dai_clkdiv,
    .set_pll = wm8960_set_dai_pll,
};

这里面东西太多，得结合现实情况来分析。