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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驱动负责处理机器特有的一些控件和音频事件（例如，当播放音频时，需要先行打开一个放大器）；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，下面就让我们从Machine驱动开始讨论吧。
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我们驱动machine platform_device 和platform_driver得注册
platform device
arch/mips/xburst/soc-x1630/common/platform.c
struct platform_device snd_alsa_device = {
.name = "ingenic-alsa",
};
platform driver
static struct snd_soc_dai_link pd_x1830_audio_dais[] = {
[0] = {
.name = "pd_x1830_audio ICDC",
.stream_name = "pd_x1830_audio ICDC",
.platform_name = "jz-asoc-aic-dma",
.cpu_dai_name = "jz-asoc-aic-i2s",
.init = pd_x1830_audio_dlv_dai_link_init,
.codec_dai_name = "icdc-d4-hifi",
.codec_name = "icdc-d4",
.dai_fmt = SND_SOC_DAIFMT_I2S|SND_SOC_DAIFMT_CBM_CFM,
.ops = &pd_x1830_audio_i2s_ops,
},
[1] = {
.name = "canna DMIC",
.stream_name = "canna DMIC",
.platform_name = "jz-asoc-dmic-dma",
.cpu_dai_name = "jz-asoc-dmic",
.codec_dai_name = "dmic-codec-hifi",
.codec_name = "jz-asoc-dmic",
},
};
static struct snd_soc_card pd_x1830_audio = {
.name = UNI_SOUND_CARD_NAME,
.owner = THIS_MODULE,
.dai_link = pd_x1830_audio_dais,
.num_links = ARRAY_SIZE(pd_x1830_audio_dais),
};
static int snd_pd_x1830_audio_probe(struct platform_device *pdev)
{
pd_x1830_audio.dev = &pdev->dev;
ret = snd_soc_register_card(&pd_x1830_audio); //注册声卡设备
}
static struct platform_driver snd_pd_x1830_audio_driver = {
.driver = {
.owner = THIS_MODULE,
.name = "ingenic-alsa",
.pm = &snd_soc_pm_ops,
},
.probe = snd_pd_x1830_audio_probe,
.remove = snd_pd_x1830_audio_remove,
};
module_platform_driver(snd_pd_x1830_audio_driver);
通过snd_soc_card结构，又引出了Machine驱动的另外两个个数据结构：
snd_soc_dai_link（实例：pd_x1830_audio_dais ）
snd_soc_ops（实例：pd_x1830_audio_i2s_ops ）
其中，snd_soc_dai_link中，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，这些注册的部件都是在另外相应的Platform驱动和Codec驱动的代码文件中定义的，这样看来，Machine驱动的设备初始化代码无非就是选择合适Platform和Codec以及dai，用他们填充以上几个数据结构，然后注册Platform设备即可。当然还要实现连接Platform和Codec的dai_link对应的ops实现，本例就是pd_x1830_audio_i2s_ops，它只实现了hw_params函数：pd_x1830_audio_i2s_hw_params。
sound/soc/soc-core.c
static int __init snd_soc_init(void)
{
return platform_driver_register(&soc_driver); //这个驱动的probe我们没有走
}
static int soc_probe(struct platform_device *pdev)
分析我们probe干的活
static int snd_pd_x1830_audio_probe(struct platform_device *pdev)
{
pd_x1830_audio.dev = &pdev->dev;
ret = snd_soc_register_card(&pd_x1830_audio); //注册声卡设备
}
int snd_soc_register_card(struct snd_soc_card *card)
{
for (i = 0; i < card->num_links; i++) {
struct snd_soc_dai_link *link = &card->dai_link[i];
/*
* Codec must be specified by 1 of name or OF node,
* not both or neither.
*/
if (!!link->codec_name == !!link->codec_of_node) {
dev_err(card->dev, "ASoC: Neither/both codec"
" name/of_node are set for %s\n", link->name);
return -EINVAL;
}
/* Codec DAI name must be specified */
if (!link->codec_dai_name) {
dev_err(card->dev, "ASoC: codec_dai_name not"
" set for %s\n", link->name);
return -EINVAL;
}
/*
* Platform may be specified by either name or OF node, but
* can be left unspecified, and a dummy platform will be used.
*/
if (link->platform_name && link->platform_of_node) {
dev_err(card->dev, "ASoC: Both platform name/of_node"
" are set for %s\n", link->name);
return -EINVAL;
}
/*
* CPU device may be specified by either name or OF node, but
* can be left unspecified, and will be matched based on DAI
* name alone..
*/
if (link->cpu_name && link->cpu_of_node) {
dev_err(card->dev, "ASoC: Neither/both "
"cpu name/of_node are set for %s\n",link->name);
return -EINVAL;
}
/*
* At least one of CPU DAI name or CPU device name/node must be
* specified
*/
if (!link->cpu_dai_name &&
!(link->cpu_name || link->cpu_of_node)) {
dev_err(card->dev, "ASoC: Neither cpu_dai_name nor "
"cpu_name/of_node are set for %s\n", link->name);
return -EINVAL;
}
}
snd_soc_initialize_card_lists(card);
//系统中所有的Codec、DAI、Platform都在注册时连接到这三个全局链表上
INIT_LIST_HEAD(&card->dai_dev_list);
INIT_LIST_HEAD(&card->codec_dev_list);
INIT_LIST_HEAD(&card->platform_dev_list);
INIT_LIST_HEAD(&card->widgets);
INIT_LIST_HEAD(&card->paths);
INIT_LIST_HEAD(&card->dapm_list);
card->rtd = devm_kzalloc(card->dev, sizeof(struct snd_soc_pcm_runtime) * (card->num_links + card->num_aux_devs), GFP_KERNEL);
for (i = 0; i < card->num_links; i++)
card->rtd[i].dai_link = &card->dai_link[i];
INIT_LIST_HEAD(&card->list);
INIT_LIST_HEAD(&card->dapm_dirty);
card->instantiated = 0;
mutex_init(&card->mutex);
mutex_init(&card->dapm_mutex);
ret = snd_soc_instantiate_card(card);
if (ret != 0)
soc_cleanup_card_debugfs(card);
return ret;
}
//snd_pd_x1830_audio_probe函数本身很简单，通过snd_soc_register_card，为snd_soc_pcm_runtime数组申请内存，每一个dai_link对应snd_soc_pcm_runtime数组的一个单元，然后把snd_soc_card中的dai_link配置复制到相应的snd_soc_pcm_runtime中，最后，大部分的工作都在snd_soc_instantiate_card中实现，下面就看看snd_soc_instantiate_card做了些什么：
static int snd_soc_instantiate_card(struct snd_soc_card *card)
{
/* bind DAIs */
for (i = 0; i < card->num_links; i++) {
ret = soc_bind_dai_link(card, i);
if (ret != 0)
goto base_error;
}
//ASoC定义了三个全局的链表头变量：codec_list、dai_list、platform_list，系统中所有的Codec、DAI、Platform都在注册时连接到这三个全局链表上。soc_bind_dai_link函数逐个扫描这三个链表，根据card->dai_link[]中的名称进行匹配，匹配后把相应的codec，dai和platform实例赋值到card->rtd[]中（snd_soc_pcm_runtime）。经过这个过程后，snd_soc_pcm_runtime：（card->rtd）中保存了本Machine中使用的Codec，DAI和Platform驱动的信息
/* initialize the register cache for each available codec */
list_for_each_entry(codec, &codec_list, list) {
if (codec->cache_init)
continue;
/* by default we don't override the compress_type */
compress_type = 0;
/* check to see if we need to override the compress_type */
for (i = 0; i < card->num_configs; ++i) {
codec_conf = &card->codec_conf[i];
if (!strcmp(codec->name, codec_conf->dev_name)) {
compress_type = codec_conf->compress_type;
if (compress_type && compress_type
!= codec->compress_type)
break;
}
}
ret = snd_soc_init_codec_cache(codec, compress_type);
if (ret < 0)
goto base_error;
}
/* card bind complete so register a sound card */
ret = snd_card_create(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;
}
card->snd_card->dev = card->dev;
card->dapm.bias_level = SND_SOC_BIAS_OFF;
card->dapm.dev = card->dev;
card->dapm.card = card;
list_add(&card->dapm.list, &card->dapm_list);
//初始化Codec的寄存器缓存，然后调用标准的alsa函数创建声卡实例
/* initialise the sound card only once */
if (card->probe) {
ret = card->probe(card); //依次调用各个子结构的probe函数
if (ret < 0)
goto card_probe_error;
}
//
/* probe all components used by DAI links on this card */
for (order = SND_SOC_COMP_ORDER_FIRST; order <= SND_SOC_COMP_ORDER_LAST;
order++) {
for (i = 0; i < card->num_links; i++) {
ret = soc_probe_link_components(card, i, order);
//ret = soc_probe_codec(card, cpu_dai->codec); --->codec->driver->probe
ret = soc_probe_platform(card, platform);--->platform->driver->probe
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 */
for (order = SND_SOC_COMP_ORDER_FIRST; order <= SND_SOC_COMP_ORDER_LAST;
order++) {
for (i = 0; i < card->num_links; i++) {
ret = soc_probe_link_dais(card, i, order);
//cpu_dai->driver->probe
//codec_dai->driver->probe
if (ret < 0) {
dev_err(card->dev,
"ASoC: failed to instantiate card %d\n",
ret);
goto probe_dai_err;
}
}
}
}
static int soc_probe_link_dais(struct snd_soc_card *card, int num, int order) //该函数出了挨个调用了codec，dai和platform驱动的probe函数 cpu_dai->driver->probe codec_dai->driver->probe
{
/* probe the cpu_dai */
if (!cpu_dai->probed &&
cpu_dai->driver->probe_order == order) {
if (!cpu_dai->codec) {
cpu_dai->dapm.card = card;
if (!try_module_get(cpu_dai->dev->driver->owner))
return -ENODEV;
list_add(&cpu_dai->dapm.list, &card->dapm_list);
snd_soc_dapm_new_dai_widgets(&cpu_dai->dapm, cpu_dai);
}
if (cpu_dai->driver->probe) {
ret = cpu_dai->driver->probe(cpu_dai);
if (ret < 0) {
dev_err(cpu_dai->dev,
"ASoC: failed to probe CPU DAI %s: %d\n",
cpu_dai->name, ret);
module_put(cpu_dai->dev->driver->owner);
return ret;
}
}
cpu_dai->probed = 1;
/* mark cpu_dai as probed and add to card dai list */
list_add(&cpu_dai->card_list, &card->dai_dev_list);
}
/* probe the CODEC DAI */
if (!codec_dai->probed && codec_dai->driver->probe_order == order) {
if (codec_dai->driver->probe) {
ret = codec_dai->driver->probe(codec_dai);
if (ret < 0) {
dev_err(codec_dai->dev,
"ASoC: failed to probe CODEC DAI %s: %d\n",
codec_dai->name, ret);
return ret;
}
/* mark codec_dai as probed and add to card dai list */
codec_dai->probed = 1;
list_add(&codec_dai->card_list, &card->dai_dev_list);
}
if (!dai_link->params) {
/* create the pcm */
ret = soc_new_pcm(rtd, num);
if (ret < 0) {
dev_err(card->dev, "ASoC: can't create pcm %s :%d\n",
dai_link->stream_name, ret);
return ret;
}
//该函数出了挨个调用了codec，dai和platform驱动的probe函数外，在最后还调用了soc_new_pcm()函数用于创建标准alsa驱动的pcm逻辑设备
if (!dai_link->params) {
/* create the pcm */
ret = soc_new_pcm(rtd, num);
if (ret < 0) {
dev_err(card->dev, "ASoC: can't create pcm %s :%d\n",
dai_link->stream_name, ret);
return ret;
}
} else {
/* link the DAI widgets */
play_w = codec_dai->playback_widget;
capture_w = cpu_dai->capture_widget;
if (play_w && capture_w) {
ret = snd_soc_dapm_new_pcm(card, dai_link->params,
capture_w, play_w);
if (ret != 0) {
dev_err(card->dev, "ASoC: Can't link %s to %s: %d\n",
play_w->name, capture_w->name, ret);
return ret;
}
}
play_w = cpu_dai->playback_widget;
capture_w = codec_dai->capture_widget;
if (play_w && capture_w) {
ret = snd_soc_dapm_new_pcm(card, dai_link->params,
capture_w, play_w);
if (ret != 0) {
dev_err(card->dev, "ASoC: Can't link %s to %s: %d\n",
play_w->name, capture_w->name, ret);
return ret;
}
}
}
}
//成snd_card和snd_pcm的创建后，接着对dapm和dai支持的格式做出一些初始化合设置工作后，调用了 card->late_probe(card)进行一些最后的初始化合设置工作
}
int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
{
//该函数首先初始化snd_soc_runtime中的snd_pcm_ops字段，也就是rtd->ops中的部分成员，例如open，close，hw_params等，紧接着调用标准alsa驱动中的创建pcm的函数snd_pcm_new()创建声卡的pcm实例，pcm的private_data字段设置为该runtime变量rtd，然后用platform驱动中的snd_pcm_ops替换部分pcm中的snd_pcm_ops字段，最后，调用platform驱动的pcm_new回调，该回调实现该platform下的dma内存申请和dma初始化等相关工作。到这里，声卡和他的pcm实例创建完成。
}
整个Machine驱动的初始化已经完成，通过各个子结构的probe调用，实际上，也完成了部分Platfrom驱动和Codec驱动的初始化工作，整个过程可以用一下的序列图表示
static int soc_probe_link_components(struct snd_soc_card *card, int num,int order)
{
ret = soc_probe_codec(card, cpu_dai->codec); --->codec->driver->probe
ret = soc_probe_platform(card, platform);--->platform->driver->probe
}
static int soc_probe_link_dais(struct snd_soc_card *card, int num, int order)
{
//该函数出了挨个调用了codec，dai和platform驱动的probe函数 cpu_dai->driver->probe codec_dai->driver->probe
}
总结：
sound/soc/ingenic/asoc-board/pd_x1830_audio_icdc.c
platform driver
static struct snd_soc_dai_link pd_x1830_audio_dais[] = {
[0] = {
.name = "pd_x1830_audio ICDC",
.stream_name = "pd_x1830_audio ICDC",
.platform_name = "jz-asoc-aic-dma",
.cpu_dai_name = "jz-asoc-aic-i2s",
.init = pd_x1830_audio_dlv_dai_link_init,
.codec_dai_name = "icdc-d4-hifi",
.codec_name = "icdc-d4",
.dai_fmt = SND_SOC_DAIFMT_I2S|SND_SOC_DAIFMT_CBM_CFM,
.ops = &pd_x1830_audio_i2s_ops,
},
.cpu_dai_name = "jz-asoc-aic-i2s",
sound/soc/ingenic/asoc-v12/asoc-i2s-v12.c
static struct platform_driver jz_i2s_plat_driver = {
.probe = jz_i2s_platfrom_probe,
.remove = jz_i2s_platfom_remove,
.driver = {
.name = "jz-asoc-aic-i2s",
.owner = THIS_MODULE,
},
};
.platform_name = "jz-asoc-aic-dma",
sound/soc/ingenic/asoc-dma-hrtimer.c
static const struct platform_device_id jz_dma_id_table[] = {
{
.name = "jz-asoc-aic-dma", /*aic dma*/
},
{
.name = "jz-asoc-pcm-dma", /*pcmc dma*/
},
{
.name = "jz-asoc-dmic-dma", /*dmic dma*/
},
{},
};
.codec_name = "icdc-d4", 内部codec驱动
sound/soc/ingenic/icodec/icdc_d4.c
static struct platform_driver icdc_d4_codec_driver = {
.driver = {
.name = "icdc-d4",
.owner = THIS_MODULE,
},
.probe = icdc_d4_platform_probe,
.remove = icdc_d4_platform_remove,
};
.codec_dai_name = "icdc-d4-hifi"
sound/soc/ingenic/icodec/icdc_d4.c
static struct snd_soc_dai_driver icdc_d4_codec_dai = {
.name = "icdc-d4-hifi",
.playback = {
.stream_name = "Playback",
.channels_min = 2,
.channels_max = 2,
.rates = ICDC_D4_RATE,
.formats = ICDC_D4_FORMATS,
},
.capture = {
.stream_name = "Capture",
.channels_min = 1,
.channels_max = 2,
.rates = ICDC_D4_RATE,
.formats = ICDC_D4_FORMATS,
},
.symmetric_rates = 1,
.ops = &icdc_d4_dai_ops,
};