ASOC之Codec
概述
ASOC的出現是為了讓Codec獨立於CPU，減少和CPU之間的耦合，這樣同一個Codec驅動無需修改就可以適用任何一款平臺。還是以下圖做參考例子:
在Machine中已經知道，snd_soc_dai_link結構就指明瞭該Machine所使用的Platform和Codec。在Codec這邊通過codec_dai和Platform側的cpu_dai相互通訊，既然相互通訊，就需要遵守一定的規則，其中codec_dai和cpu_dai統一抽象為struct snd_soc_dai結構，而將dai的相關操作使用snd_soc_dai_driver抽象。同時也需要對所有的codec裝置進行抽象封裝，linux使用snd_soc_codec進行所有codec裝置的抽象，而將codec的驅動抽象為snd_soc_codec_driver結構。
所有簡單來說，Codec側有四個重要的資料結構:
struct snd_soc_dai，struct snd_soc_dai_driver，struct snd_soc_codec，struct snd_soc_codec_driver。
Codec程式碼分析
如何找到codec的程式碼呢？ 答案是通過machine中的snd_soc_dai_link結構:
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", };
在核心中搜索codec_name=“uda134x-codec”，會在kernel/sound/soc/codec/uda134x.c中發現。
static struct platform_driver uda134x_codec_driver = {
.driver = {
.name = "uda134x-codec",
.owner = THIS_MODULE,
},
.probe = uda134x_codec_probe,
.remove = uda134x_codec_remove,
};
之間檢視此platform_driver的probe函式
static int uda134x_codec_probe(struct platform_device *pdev) { return snd_soc_register_codec(&pdev->dev, &soc_codec_dev_uda134x, &uda134x_dai, 1); }
此出通過snd_soc_register_codec函式註冊了uda134x的codec，同時傳入了snd_soc_codec_driver和snd_soc_dai_driver結構。
static struct snd_soc_codec_driver soc_codec_dev_uda134x = {
.probe = uda134x_soc_probe,
.remove = uda134x_soc_remove,
.suspend = uda134x_soc_suspend,
.resume = uda134x_soc_resume,
.reg_cache_size = sizeof(uda134x_reg),
.reg_word_size = sizeof(u8),
.reg_cache_default = uda134x_reg,
.reg_cache_step = 1,
.read = uda134x_read_reg_cache,
.write = uda134x_write,
.set_bias_level = uda134x_set_bias_level,
.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結構:
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,
};
繼續進入snd_soc_register_codec函式分析。
-
分配一個snd_soc_codec結構，設定component引數。
codec = kzalloc(sizeof(struct snd_soc_codec), GFP_KERNEL);
if (codec == NULL)
return -ENOMEM;
codec->component.dapm_ptr = &codec->dapm;
codec->component.codec = codec； -
呼叫snd_soc_component_initialize函式進行component部件的初始化，會根據snd_soc_codec_driver中的struct snd_soc_component_driver結構設定snd_soc_codec中的component元件，詳細程式碼不在貼出。
ret = snd_soc_component_initialize(&codec->component,
&codec_drv->component_driver, dev); -
根據snd_soc_codec_driver的引數，進行一系列的初始化，
if (codec_drv->controls) {
codec->component.controls = codec_drv->controls;
codec->component.num_controls = codec_drv->num_controls;
}
if (codec_drv->dapm_widgets) {
codec->component.dapm_widgets = codec_drv->dapm_widgets;
codec->component.num_dapm_widgets = codec_drv->num_dapm_widgets;
}
if (codec_drv->dapm_routes) {
codec->component.dapm_routes = codec_drv->dapm_routes;
codec->component.num_dapm_routes = codec_drv->num_dapm_routes;
}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->write)
codec->component.write = snd_soc_codec_drv_write;
if (codec_drv->read)
codec->component.read = snd_soc_codec_drv_read;
codec->component.ignore_pmdown_time = codec_drv->ignore_pmdown_time;
codec->dapm.idle_bias_off = codec_drv->idle_bias_off;
codec->dapm.suspend_bias_off = codec_drv->suspend_bias_off;
if (codec_drv->seq_notifier)
codec->dapm.seq_notifier = codec_drv->seq_notifier;
if (codec_drv->set_bias_level)
codec->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;
mutex_init(&codec->mutex); -
根據snd_soc_dai_driver中的引數設定Format
for (i = 0; i < num_dai; i++) {
fixup_codec_formats(&dai_drv[i].playback);
fixup_codec_formats(&dai_drv[i].capture);
} -
呼叫snd_soc_register_dais介面註冊dai，傳入引數有dai的驅動，以及dai的引數，因為一個codec不止一個dai介面。
ret = snd_soc_register_dais(&codec->component, dai_drv, num_dai, false);
if (ret < 0) {
dev_err(dev, “ASoC: Failed to regster DAIs: %d\n”, ret);
goto err_cleanup;
}
根據dai的數目，分配snd_soc_dai結構，根據dai的數目設定dai的名字，這是dai的傳入引數驅動，然後將此dai加入到component的dai_list中。
for (i = 0; i < count; i++) {
dai = kzalloc(sizeof(struct snd_soc_dai), GFP_KERNEL);
if (dai == NULL) {
ret = -ENOMEM;
goto err;
}
/*
* 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 (count == 1 && legacy_dai_naming) {
dai->name = fmt_single_name(dev, &dai->id);
} else {
dai->name = fmt_multiple_name(dev, &dai_drv[i]);
if (dai_drv[i].id)
dai->id = dai_drv[i].id;
else
dai->id = i;
}
if (dai->name == NULL) {
kfree(dai);
ret = -ENOMEM;
goto err;
}
dai->component = component;
dai->dev = dev;
dai->driver = &dai_drv[i];
if (!dai->driver->ops)
dai->driver->ops = &null_dai_ops;
list_add(&dai->list, &component->dai_list);
dev_dbg(dev, "ASoC: Registered DAI '%s'\n", dai->name);
}
6. 根據component的dai_list，對所有的dai設定其所屬的codec。
list_for_each_entry(dai, &codec->component.dai_list, list)
dai->codec = codec;
- 將所有的組間加入到component_list中，然後將註冊的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);
至此，codec的註冊就分析完畢。
總結： 通過呼叫snd_soc_register_codec函式之後，分配的codec最終放入了codec_list連結串列中，codec下的component元件全部放入component_list連結串列中，codec下的dai全部存放入code->component.dai_list中。 可以在上節的Machine中看到，machine匹配codec_dai和cpu_dai也是從code->component.dai_list中獲取的。
關於codec側驅動總結:
- 分配名字為"codec_name"的平臺驅動，註冊。
- 定義struct snd_soc_codec_driver結構，設定，初始化。
- 定義struct snd_soc_dai_driver結構，設定，初始化。
- 呼叫snd_soc_register_codec函式註冊codec。
轉自https://blog.csdn.net/longwang155069/article/details/53421857