1. 概述

ASOC的出现是为了让Codec独立于CPU，减少和CPU之间的耦合，这样同一个Codec驱动无需修改就可以适用任何一款平台。还是以下图做参考例子:

在Machine中已经知道，snd_soc_dai_link结构就指明了该Machine所使用的Platform和Codec。在Codec这边通过codec_dai和Platform侧的cpu_dai相互通信，既然相互通信，就需要遵守一定的规则，其中codec_dai和cpu_dai统一抽象为struct snd_soc_dai结构，而将dai的相关操作使用snd_soc_dai_driver抽象。同时也需要对所有的codec设备进行抽象封装，linux使用snd_soc_codec进行所有codec设备的抽象，而将codec的驱动抽象为snd_soc_codec_driver结构。

所有简单来说，Codec侧有四个重要的数据结构:

struct snd_soc_dai，struct snd_soc_dai_driver，struct snd_soc_codec，struct snd_soc_codec_driver。

分析例子：

machine: sound\soc\samsung\s3c24xx_uda134x.c

platform: sound\soc\samsung\s3c24xx-i2s.c

codec: sound\soc\codecs\uda134x.c

2. Codec代码分析

如何找到codec的代码呢？答案是通过machine中的snd_soc_dai_link结构:

static struct snd_soc_dai_link s3c24xx_uda134x_dai_link = {  .name = "UDA134X",  .stream_name = "UDA134X",  .codec_name = "uda134x-codec",  .codec_dai_name = "uda134x-hifi",  .cpu_dai_name = "s3c24xx-iis",  .ops = &s3c24xx_uda134x_ops,  .platform_name  = "s3c24xx-iis",
};

在内核中搜索codec_name="uda134x-codec"，会在kernel/sound/soc/codec/uda134x.c中发现。

static struct platform_driver uda134x_codec_driver = {.driver = {.name = "uda134x-codec",},.probe = uda134x_codec_probe,.remove = uda134x_codec_remove,
};

之间查看此platform_driver的probe函数。

static int uda134x_codec_probe(struct platform_device *pdev)
{struct uda134x_platform_data *pd = pdev->dev.platform_data;struct uda134x_priv *uda134x;int ret;if (!pd) {dev_err(&pdev->dev, "Missing L3 bitbang function\n");return -ENODEV;}uda134x = devm_kzalloc(&pdev->dev, sizeof(*uda134x), GFP_KERNEL);if (!uda134x)return -ENOMEM;uda134x->pd = pd;platform_set_drvdata(pdev, uda134x);if (pd->l3.use_gpios) {ret = l3_set_gpio_ops(&pdev->dev, &uda134x->pd->l3);if (ret < 0)return ret;}uda134x->regmap = devm_regmap_init(&pdev->dev, NULL, pd,&uda134x_regmap_config);if (IS_ERR(uda134x->regmap))return PTR_ERR(uda134x->regmap);return snd_soc_register_codec(&pdev->dev,&soc_codec_dev_uda134x, &uda134x_dai, 1);
}

此出通过snd_soc_register_codec函数注册了uda134x的codec，同时传入了snd_soc_codec_driver和snd_soc_dai_driver结构。

static const struct snd_soc_codec_driver soc_codec_dev_uda134x = {.probe =        uda134x_soc_probe,.set_bias_level = uda134x_set_bias_level,.suspend_bias_off = true,.component_driver = {.dapm_widgets        = uda134x_dapm_widgets,.num_dapm_widgets   = ARRAY_SIZE(uda134x_dapm_widgets),.dapm_routes        = uda134x_dapm_routes,.num_dapm_routes = ARRAY_SIZE(uda134x_dapm_routes),},
};

snd_soc_dai_driver结构:

static const struct snd_soc_dai_ops uda134x_dai_ops = {.startup = uda134x_startup,.shutdown    = uda134x_shutdown,.hw_params  = uda134x_hw_params,.digital_mute  = uda134x_mute,.set_sysclk = uda134x_set_dai_sysclk,.set_fmt  = uda134x_set_dai_fmt,
};static struct snd_soc_dai_driver uda134x_dai = {.name = "uda134x-hifi",/* playback capabilities */.playback = {.stream_name = "Playback",.channels_min = 1,.channels_max = 2,.rates = UDA134X_RATES,.formats = UDA134X_FORMATS,},/* capture capabilities */.capture = {.stream_name = "Capture",.channels_min = 1,.channels_max = 2,.rates = UDA134X_RATES,.formats = UDA134X_FORMATS,},/* pcm operations */.ops = &uda134x_dai_ops,
};

2.1 snd_soc_register_codec


/*** snd_soc_register_codec - Register a codec with the ASoC core** @dev: The parent device for this codec* @codec_drv: Codec driver* @dai_drv: The associated DAI driver* @num_dai: Number of DAIs*/
int snd_soc_register_codec(struct device *dev,const struct snd_soc_codec_driver *codec_drv,struct snd_soc_dai_driver *dai_drv,int num_dai)
{struct snd_soc_dapm_context *dapm;struct snd_soc_codec *codec;struct snd_soc_dai *dai;int ret, i;dev_dbg(dev, "codec register %s\n", dev_name(dev));codec = kzalloc(sizeof(struct snd_soc_codec), GFP_KERNEL);if (codec == NULL)return -ENOMEM;codec->component.codec = codec;ret = snd_soc_component_initialize(&codec->component,&codec_drv->component_driver, dev);if (ret)goto err_free;if (codec_drv->probe)codec->component.probe = snd_soc_codec_drv_probe;if (codec_drv->remove)codec->component.remove = snd_soc_codec_drv_remove;if (codec_drv->suspend)codec->component.suspend = snd_soc_codec_drv_suspend;if (codec_drv->resume)codec->component.resume = snd_soc_codec_drv_resume;if (codec_drv->write)codec->component.write = snd_soc_codec_drv_write;if (codec_drv->read)codec->component.read = snd_soc_codec_drv_read;if (codec_drv->set_sysclk)codec->component.set_sysclk = snd_soc_codec_set_sysclk_;if (codec_drv->set_pll)codec->component.set_pll = snd_soc_codec_set_pll_;if (codec_drv->set_jack)codec->component.set_jack = snd_soc_codec_set_jack_;codec->component.ignore_pmdown_time = codec_drv->ignore_pmdown_time;dapm = snd_soc_codec_get_dapm(codec);dapm->idle_bias_off = codec_drv->idle_bias_off;dapm->suspend_bias_off = codec_drv->suspend_bias_off;if (codec_drv->seq_notifier)dapm->seq_notifier = codec_drv->seq_notifier;if (codec_drv->set_bias_level)dapm->set_bias_level = snd_soc_codec_set_bias_level;codec->dev = dev;codec->driver = codec_drv;codec->component.val_bytes = codec_drv->reg_word_size;#ifdef CONFIG_DEBUG_FScodec->component.init_debugfs = soc_init_codec_debugfs;codec->component.debugfs_prefix = "codec";
#endifif (codec_drv->get_regmap)codec->component.regmap = codec_drv->get_regmap(dev);for (i = 0; i < num_dai; i++) {fixup_codec_formats(&dai_drv[i].playback);fixup_codec_formats(&dai_drv[i].capture);}ret = snd_soc_register_dais(&codec->component, dai_drv, num_dai, false);if (ret < 0) {dev_err(dev, "ASoC: Failed to register DAIs: %d\n", ret);goto err_cleanup;}list_for_each_entry(dai, &codec->component.dai_list, list)dai->codec = codec;mutex_lock(&client_mutex);snd_soc_component_add_unlocked(&codec->component);list_add(&codec->list, &codec_list);mutex_unlock(&client_mutex);dev_dbg(codec->dev, "ASoC: Registered codec '%s'\n",codec->component.name);return 0;err_cleanup:snd_soc_component_cleanup(&codec->component);
err_free:kfree(codec);return ret;
}

2.1.1 分配一个snd_soc_codec结构，设置其component参数

 codec = kzalloc(sizeof(struct snd_soc_codec), GFP_KERNEL);if (codec == NULL)return -ENOMEM;codec->component.codec = codec;

2.1.2 调用snd_soc_component_initialize函数进行component部件的初始化

 ret = snd_soc_component_initialize(&codec->component,&codec_drv->component_driver, dev);if (ret)goto err_free;

2.1.3 根据snd_soc_codec_driver的参数，进行一系列的初始化

 if (codec_drv->probe)codec->component.probe = snd_soc_codec_drv_probe;if (codec_drv->remove)codec->component.remove = snd_soc_codec_drv_remove;if (codec_drv->suspend)codec->component.suspend = snd_soc_codec_drv_suspend;if (codec_drv->resume)codec->component.resume = snd_soc_codec_drv_resume;if (codec_drv->write)codec->component.write = snd_soc_codec_drv_write;if (codec_drv->read)codec->component.read = snd_soc_codec_drv_read;if (codec_drv->set_sysclk)codec->component.set_sysclk = snd_soc_codec_set_sysclk_;if (codec_drv->set_pll)codec->component.set_pll = snd_soc_codec_set_pll_;if (codec_drv->set_jack)codec->component.set_jack = snd_soc_codec_set_jack_;codec->component.ignore_pmdown_time = codec_drv->ignore_pmdown_time;dapm = snd_soc_codec_get_dapm(codec);dapm->idle_bias_off = codec_drv->idle_bias_off;dapm->suspend_bias_off = codec_drv->suspend_bias_off;if (codec_drv->seq_notifier)dapm->seq_notifier = codec_drv->seq_notifier;if (codec_drv->set_bias_level)dapm->set_bias_level = snd_soc_codec_set_bias_level;codec->dev = dev;codec->driver = codec_drv;codec->component.val_bytes = codec_drv->reg_word_size;

2.1.4 根据snd_soc_dai_driver中的参数设置Format

 for (i = 0; i < num_dai; i++) {fixup_codec_formats(&dai_drv[i].playback);fixup_codec_formats(&dai_drv[i].capture);}

2.1.5 调用snd_soc_register_dais接口注册dai

 ret = snd_soc_register_dais(&codec->component, dai_drv, num_dai, false);if (ret < 0) {dev_err(dev, "ASoC: Failed to register DAIs: %d\n", ret);goto err_cleanup;}

根据dai的数目，分配snd_soc_dai结构，根据dai的数目设置dai的名字，这是dai的传入参数驱动，然后将此dai加入到component的dai_list中。


/* Create a DAI and add it to the component's DAI list */
static struct snd_soc_dai *soc_add_dai(struct snd_soc_component *component,struct snd_soc_dai_driver *dai_drv,bool legacy_dai_naming)
{struct device *dev = component->dev;struct snd_soc_dai *dai;dev_dbg(dev, "ASoC: dynamically register DAI %s\n", dev_name(dev));dai = kzalloc(sizeof(struct snd_soc_dai), GFP_KERNEL);if (dai == NULL)return NULL;/** Back in the old days when we still had component-less DAIs,* instead of having a static name, component-less DAIs would* inherit the name of the parent device so it is possible to* register multiple instances of the DAI. We still need to keep* the same naming style even though those DAIs are not* component-less anymore.*/if (legacy_dai_naming &&(dai_drv->id == 0 || dai_drv->name == NULL)) {dai->name = fmt_single_name(dev, &dai->id);} else {dai->name = fmt_multiple_name(dev, dai_drv);if (dai_drv->id)dai->id = dai_drv->id;elsedai->id = component->num_dai;}if (dai->name == NULL) {kfree(dai);return NULL;}dai->component = component;dai->dev = dev;dai->driver = dai_drv;if (!dai->driver->ops)dai->driver->ops = &null_dai_ops;list_add(&dai->list, &component->dai_list);component->num_dai++;dev_dbg(dev, "ASoC: Registered DAI '%s'\n", dai->name);return dai;
}

2.1.6 根据component的dai_list，对所有的dai设置其所属的codec

 list_for_each_entry(dai, &codec->component.dai_list, list)dai->codec = codec;

2.1.7 将所有的组间加入到component_list中，然后将注册的codec存入codec_list中

mutex_lock(&client_mutex);
snd_soc_component_add_unlocked(&codec->component);
list_add(&codec->list, &codec_list);
mutex_unlock(&client_mutex);

3. 总结

总结：通过调用snd_soc_register_codec函数之后，分配的codec最终放入了codec_list链表中，codec下的component组件全部放入component_list链表中，codec下的dai全部存放入code->component.dai_list中。可以在上节的Machine中看到，machine匹配codec_dai和cpu_dai也是从code->component.dai_list中获取的。

关于codec侧驱动总结:

1. 分配名字为"codec_name"的平台驱动，注册。
2. 定义struct snd_soc_codec_driver结构，设置，初始化。

3. 定义struct snd_soc_dai_driver结构，设置，初始化。

4. 调用snd_soc_register_codec函数注册codec。

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