ASOC machine部分工作

由前面可知，ASoC被分为Machine、Platform和Codec三大部分,其中的Machine驱动负责Platform和Codec之间的耦合以及部分和设备或板子特定的代码，Machine为CPU、Codec、输入输出设备提供了一个载体。单独的Platform和Codec驱动是不能工作的，它必须由Machine驱动把它们结合在一起才能完成整个设备的音频处理工作。ASoC的一切都从Machine驱动开始，包括声卡的注册，绑定Platform和Codec驱动等等。

Machine关键数据结构如下

//代表 Machine
struct snd_soc_card 

//rtd 记录单个完整链路的组成信息(codec，platform，dais)
struct snd_soc_pcm_runtime *rtd;

//用于创建CPU　DAI　和　Codec DAI的连接
struct snd_soc_dai_link

以WM8994的一款Samsung的开发板SMDK为例子做说明,WM8994是一颗Wolfson生产的多功能Codec芯片。

kernel\sound\soc\samsung\smdk_wm8994.c

/*
 * SMDK WM8994 DAI operations.
 */
static struct snd_soc_ops smdk_ops = {
	.hw_params = smdk_hw_params,
};

/*
指定了Platform、Codec、codec_dai、cpu_dai的名字
稍后Machine驱动将会利用这些名字去匹配已经在系统中注册的platform，codec，dai
*/
static struct snd_soc_dai_link smdk_dai[] = {
	{ /* Primary DAI i/f */
		.name = "WM8994 AIF1",
		.stream_name = "Pri_Dai",
		.cpu_dai_name = "samsung-i2s.0",
		.codec_dai_name = "wm8994-aif1",
		.platform_name = "samsung-i2s.0",
		.codec_name = "wm8994-codec",
		.init = smdk_wm8994_init_paiftx,
		.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF |
			SND_SOC_DAIFMT_CBM_CFM,
		.ops = &smdk_ops,
	}, { /* Sec_Fifo Playback i/f */
		.name = "Sec_FIFO TX",
		.stream_name = "Sec_Dai",
		.cpu_dai_name = "samsung-i2s-sec",
		.codec_dai_name = "wm8994-aif1",
		.platform_name = "samsung-i2s-sec",
		.codec_name = "wm8994-codec",
		.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF |
			SND_SOC_DAIFMT_CBM_CFM,
		.ops = &smdk_ops, //！！！
	},
};

//machine 
static struct snd_soc_card smdk = {
	.name = "SMDK-I2S",
	.owner = THIS_MODULE,
	.dai_link = smdk_dai, //snd_soc_dai_link
	.num_links = ARRAY_SIZE(smdk_dai),//2
};


static int smdk_audio_probe(struct platform_device *pdev)
{
	
	struct snd_soc_card *card = &smdk;
	
	card->dev = &pdev->dev;
	
	/*
		struct platform_device *pdev
			struct device	dev;

		struct snd_soc_card *card
	*/
	ret = devm_snd_soc_register_card(&pdev->dev, card);
	
}


static struct platform_driver smdk_audio_driver = {
	.driver		= {
		.name	= "smdk-audio-wm8994",
		.of_match_table = of_match_ptr(samsung_wm8994_of_match),
		.pm	= &snd_soc_pm_ops,
	},
	.probe		= smdk_audio_probe,
};

module_platform_driver(smdk_audio_driver);

kernel\sound\soc\soc-devres.c

/*
	struct platform_device *pdev
		struct device	dev;

	struct snd_soc_card *card
*/
int devm_snd_soc_register_card(struct device *dev, struct snd_soc_card *card)
{
	struct snd_soc_card **ptr;
	int ret;

	ptr = devres_alloc(devm_card_release, sizeof(*ptr), GFP_KERNEL);
	if (!ptr)
		return -ENOMEM;

	ret = snd_soc_register_card(card);
	if (ret == 0) {
		*ptr = card;
		devres_add(dev, ptr);
	} else {
		devres_free(ptr);
	}

	return ret;
}
EXPORT_SYMBOL_GPL(devm_snd_soc_register_card);




/**
 * snd_soc_register_card - Register a card with the ASoC core
 *
 * @card: Card to register
 *
 */
int snd_soc_register_card(struct snd_soc_card *card)
{
	int i, ret;
	struct snd_soc_pcm_runtime *rtd;

	if (!card->name || !card->dev)
		return -EINVAL;

...

	//初始化 rtd_list链表
	INIT_LIST_HEAD(&card->rtd_list);
	card->num_rtd = 0;

...

	ret = snd_soc_instantiate_card(card);
	if (ret != 0)
		return ret;

...
	return ret;
}
EXPORT_SYMBOL_GPL(snd_soc_register_card);

//主要工作就在这里 ！！！

static int snd_soc_instantiate_card(struct snd_soc_card *card)
{
	struct snd_soc_pcm_runtime *rtd;
	struct snd_soc_dai_link *dai_link;
	int ret, i, order;

...
	/* bind DAIs */
	//1 根据指定 的 codec platform 的 dai name信息 查找已经注册的目标dai, 并得到其所属的组件(codec platform)。全部整到 snd_soc_pcm_runtime 
	for (i = 0; i < card->num_links; i++) {
		
		/*
		根据snd_soc_dai_link结构体中的name，到全局组件链表中找到相应的  codec_dai, cpu_dai。platform 找到之后将这些 以及 所属的 codec，platform 全部放入结构体 snd_soc_pcm_runtime 的相应位置
		很明显 本例程有两个dai_link 即会填充两个 rtd
		所以 rtd 就是用来记录单个链路(codec，platform，dais)的信息
		*/
		ret = soc_bind_dai_link(card, &card->dai_link[i]);
		
	}

...
	//2 创建声卡逻辑设备  类型：control
	/* card bind complete so register a sound card */
	ret = snd_card_new(card->dev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1,
			card->owner, 0, &card->snd_card);
	if (ret < 0) {
		dev_err(card->dev,
			"ASoC: can't create sound card for card %s: %d\n",
			card->name, ret);
		goto base_error;
	}

...


	/* probe all components used by DAI links on this card */
	//3 调用 platform  codec  的probe()
	for (order = SND_SOC_COMP_ORDER_FIRST; order <= SND_SOC_COMP_ORDER_LAST;
			order++) {
		//很明显 本例程rtd_list链表上有两个 rtd 
		list_for_each_entry(rtd, &card->rtd_list, list) {
			ret = soc_probe_link_components(card, rtd, order);
			if (ret < 0) {
				dev_err(card->dev,
					"ASoC: failed to instantiate card %d\n",
					ret);
				goto probe_dai_err;
			}
		}
	}

	...



	/* probe all DAI links on this card */
	//4 调用 platform codec 的 DAIS probe()
	for (order = SND_SOC_COMP_ORDER_FIRST; order <= SND_SOC_COMP_ORDER_LAST;
			order++) {
		list_for_each_entry(rtd, &card->rtd_list, list) {
			ret = soc_probe_link_dais(card, rtd, order);
			if (ret < 0) {
				dev_err(card->dev,
					"ASoC: failed to instantiate card %d\n",
					ret);
				goto probe_dai_err;
			}
		}
	}
	
	...
	
	//5 注册声卡
	ret = snd_card_register(card->snd_card);
	if (ret < 0) {
		dev_err(card->dev, "ASoC: failed to register soundcard %d\n",
				ret);
		goto probe_aux_dev_err;
	}


	...
	return ret;
}

这里简单说说明一下 工作1和工作2。

工作1：
根据指定 的 codec platform 的 dai name信息 查找已经注册的目标dai, 并得到其所属的组件(codec platform)。全部整到 snd_soc_pcm_runtime

static int soc_bind_dai_link(struct snd_soc_card *card,
	struct snd_soc_dai_link *dai_link)
{
	struct snd_soc_pcm_runtime *rtd;
	struct snd_soc_dai_link_component *codecs = dai_link->codecs;
	struct snd_soc_dai_link_component cpu_dai_component;
	struct snd_soc_component *component;
	struct snd_soc_dai **codec_dais;
	struct device_node *platform_of_node;
	const char *platform_name;
	int i;

	if (dai_link->ignore)
		return 0;

	dev_dbg(card->dev, "ASoC: binding %s\n", dai_link->name);

	if (soc_is_dai_link_bound(card, dai_link)) {
		dev_dbg(card->dev, "ASoC: dai link %s already bound\n",
			dai_link->name);
		return 0;
	}

//创建 snd_soc_pcm_runtime
	rtd = soc_new_pcm_runtime(card, dai_link);
	if (!rtd)
		return -ENOMEM;

/*
在已注的组件链表中 遍历所有组件。依次遍历每一个组件的 dai list 链表。查找目标名字的 cpu_dai
*/
	cpu_dai_component.name = dai_link->cpu_name;
	cpu_dai_component.of_node = dai_link->cpu_of_node;
	cpu_dai_component.dai_name = dai_link->cpu_dai_name;
	rtd->cpu_dai = snd_soc_find_dai(&cpu_dai_component);
	if (!rtd->cpu_dai) {
		dev_info(card->dev, "ASoC: CPU DAI %s not registered\n",
			 dai_link->cpu_dai_name);
		goto _err_defer;
	}
	snd_soc_rtdcom_add(rtd, rtd->cpu_dai->component);

	rtd->num_codecs = dai_link->num_codecs;

	/* Find CODEC from registered CODECs */
	codec_dais = rtd->codec_dais;
	for (i = 0; i < rtd->num_codecs; i++) {
		codec_dais[i] = snd_soc_find_dai(&codecs[i]);
		if (!codec_dais[i]) {
			dev_err(card->dev, "ASoC: CODEC DAI %s not registered\n",
				codecs[i].dai_name);
			goto _err_defer;
		}
		snd_soc_rtdcom_add(rtd, codec_dais[i]->component);
	}

	/* Single codec links expect codec and codec_dai in runtime data */
	rtd->codec_dai = codec_dais[0];

	/* if there's no platform we match on the empty platform */
	platform_name = dai_link->platform_name;
	if (!platform_name && !dai_link->platform_of_node)
		platform_name = "snd-soc-dummy";

	/* find one from the set of registered platforms */
	list_for_each_entry(component, &component_list, list) {
		platform_of_node = component->dev->of_node;
		if (!platform_of_node && component->dev->parent->of_node)
			platform_of_node = component->dev->parent->of_node;

		if (dai_link->platform_of_node) {
			if (platform_of_node != dai_link->platform_of_node)
				continue;
		} else {
			if (strcmp(component->name, platform_name))
				continue;
		}

		snd_soc_rtdcom_add(rtd, component);
	}

	soc_add_pcm_runtime(card, rtd);
	return 0;

_err_defer:
	soc_free_pcm_runtime(rtd);
	return  -EPROBE_DEFER;
}


/** 搜索所有已注册的组件 和 DAIs
 * snd_soc_find_dai - Find a registered DAI
 *
 * @dlc: name of the DAI or the DAI driver and optional component info to match
 
 * 此函数将搜索所有已注册的组件及其DAIs
 * This function will search all registered components and their DAIs to
 * find the DAI of the same name. The component's of_node and name
 * should also match if being specified.
 *
 * Return: pointer of DAI, or NULL if not found.
 */
struct snd_soc_dai *snd_soc_find_dai(
	const struct snd_soc_dai_link_component *dlc)
{
	struct snd_soc_component *component;
	struct snd_soc_dai *dai;
	struct device_node *component_of_node;

	lockdep_assert_held(&client_mutex);

	/* Find CPU DAI from registered DAIs*/
	/*
	component_list 全局组件链表(包含已注册的所有组件以及DAIS)
	*/
	list_for_each_entry(component, &component_list, list) {
		component_of_node = component->dev->of_node;
		if (!component_of_node && component->dev->parent)
			component_of_node = component->dev->parent->of_node;

		if (dlc->of_node && component_of_node != dlc->of_node)
			continue;
		if (dlc->name && strcmp(component->name, dlc->name))
			continue;
		list_for_each_entry(dai, &component->dai_list, list) {
			if (dlc->dai_name && strcmp(dai->name, dlc->dai_name)
			    && (!dai->driver->name
				|| strcmp(dai->driver->name, dlc->dai_name)))
				continue;

			return dai;
		}
	}

	return NULL;
}
EXPORT_SYMBOL_GPL(snd_soc_find_dai);

工作2 创建声卡逻辑设备 类型：control

int snd_card_new(struct device *parent, int idx, const char *xid,
		    struct module *module, int extra_size,
		    struct snd_card **card_ret)
{
	//声卡设备
	struct snd_card *card;
	int err;

	if (snd_BUG_ON(!card_ret))
		return -EINVAL;
	*card_ret = NULL;

	if (extra_size < 0)
		extra_size = 0;
	card = kzalloc(sizeof(*card) + extra_size, GFP_KERNEL);
	if (!card)
		return -ENOMEM;
	if (extra_size > 0)
		card->private_data = (char *)card + sizeof(struct snd_card);

	...
	
	err = snd_ctl_create(card);

	err = snd_info_card_create(card);

	*card_ret = card;
	return 0;

      __error_ctl:
	snd_device_free_all(card);
      __error:
	put_device(&card->card_dev);
  	return err;
}
EXPORT_SYMBOL(snd_card_new);

int snd_ctl_create(struct snd_card *card)
{
	static struct snd_device_ops ops = {
		.dev_free = snd_ctl_dev_free,
		.dev_register =	snd_ctl_dev_register,
		.dev_disconnect = snd_ctl_dev_disconnect,
	};
	int err;

	if (snd_BUG_ON(!card))
		return -ENXIO;
	if (snd_BUG_ON(card->number < 0 || card->number >= SNDRV_CARDS))
		return -ENXIO;

	snd_device_initialize(&card->ctl_dev, card);
	dev_set_name(&card->ctl_dev, "controlC%d", card->number);

	//创建类型为 SNDRV_DEV_CONTROL 的 snd_device，并挂入 snd_card 的devices链表
	err = snd_device_new(card, SNDRV_DEV_CONTROL, card, &ops);
	if (err < 0)
		put_device(&card->ctl_dev);
	return err;
}

整理后
machine codec platform codec_DAI platform_DAI 以及声卡设备 声卡逻辑设备 组成如下关系：