“本文转载自：[DroidPhone]的Linux ALSA声卡驱动之六：ASoC架构中的Machine”
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。
1.注册Platform Device
ASoC把声卡注册为Platform Device，我们以一款Samsung的开发板SMDK为例子做说明（wm8580）。
1.1 初始化函数
- sound/soc/samsung/smdk_wm8580.c
static int __init smdk_audio_init(void)
{
int ret;
smdk_snd_device = platform_device_alloc("soc-audio", -1);
if (!smdk_snd_device)
return -ENOMEM;
platform_set_drvdata(smdk_snd_device, &smdk);
ret = platform_device_add(smdk_snd_device);
if (ret)
platform_device_put(smdk_snd_device);
return ret;
}
由此可见，模块初始化时，注册了一个名为soc-audio的Platform设备，同时把smdk设到platform_device结构的dev.drvdata字段中，这里引出了第一个数据结构snd_soc_card的实例smdk，他的定义如下：
- sound/soc/samsung/smdk_wm8580.c
static struct snd_soc_card smdk = {
.name = "SMDK-I2S",
.owner = THIS_MODULE,
.dai_link = smdk_dai,
.num_links = ARRAY_SIZE(smdk_dai),
.dapm_widgets = smdk_wm8580_dapm_widgets,
.num_dapm_widgets = ARRAY_SIZE(smdk_wm8580_dapm_widgets),
.dapm_routes = smdk_wm8580_audio_map,
.num_dapm_routes = ARRAY_SIZE(smdk_wm8580_audio_map),
};
通过snd_soc_card结构，又引出了Machine驱动的另外两个数据结构：
- snd_soc_dai_link（实例：smdk_dai[] ）
- snd_soc_ops（实例：smdk_ops ）
static struct snd_soc_dai_link smdk_dai[] = {
[PRI_PLAYBACK] = { /* Primary Playback i/f */
.name = "WM8580 PAIF RX",
.stream_name = "Playback",
.cpu_dai_name = "samsung-i2s.2",
.codec_dai_name = "wm8580-hifi-playback",
.platform_name = "samsung-i2s.0",
.codec_name = "wm8580.0-001b",
.dai_fmt = SMDK_DAI_FMT,
.ops = &smdk_ops,
},
[PRI_CAPTURE] = { /* Primary Capture i/f */
.name = "WM8580 PAIF TX",
.stream_name = "Capture",
.cpu_dai_name = "samsung-i2s.2",
.codec_dai_name = "wm8580-hifi-capture",
.platform_name = "samsung-i2s.0",
.codec_name = "wm8580.0-001b",
.dai_fmt = SMDK_DAI_FMT,
.init = smdk_wm8580_init_paiftx,
.ops = &smdk_ops,
},
};
------------------------------------------------------------------------------
static struct snd_soc_ops smdk_ops = {
.hw_params = smdk_hw_params,
};
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smdk_ops，它只实现了hw_params函数：smdk_hw_params。
2.注册Platform Driver
按照Linux的设备模型，有platform_device，就必定会有platform_driver。ASoC的platform_driver在以下文件中定义：sound/soc/soc-core.c。
还是先从模块的入口看起：
static int __init snd_soc_init(void)
{
snd_soc_debugfs_init();
snd_soc_util_init();
return platform_driver_register(&soc_driver);
}
soc_driver的定义如下：
/* ASoC platform driver */
static struct platform_driver soc_driver = {
.driver = {
.name = "soc-audio",
.pm = &snd_soc_pm_ops,
},
.probe = soc_probe,
.remove = soc_remove,
};
platform_driver的name字段为soc-audio，正好与platform_device中的名字一样，按照Linux的设备模型，platform总线会匹配这两个名字一样的device和driver，同时会触发soc_probe的调用，它正是整个ASoC驱动初始化的入口。
3.初始化入口soc_probe()
soc_probe函数本身很简单，它先从platform_device参数中取出snd_soc_card，然后调用snd_soc_register_card。
- sound/soc/soc-core.c
/* probes a new socdev */
static int soc_probe(struct platform_device *pdev)
{
struct snd_soc_card *card = platform_get_drvdata(pdev); // 1
/*
* no card, so machine driver should be registering card
* we should not be here in that case so ret error
*/
if (!card)
return -EINVAL;
dev_warn(&pdev->dev,
"ASoC: machine %s should use snd_soc_register_card()
",
card->name);
/* Bodge while we unpick instantiation */
card->dev = &pdev->dev;
return snd_soc_register_card(card); // 2
}
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。
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;
for (i = 0; i < card->num_links; i++) {
struct snd_soc_dai_link *link = &card->dai_link[i];
ret = soc_init_dai_link(card, link);
if (ret) {
dev_err(card->dev, "ASoC: failed to init link %s
",
link->name);
return ret;
}
}
dev_set_drvdata(card->dev, card);
snd_soc_initialize_card_lists(card);
INIT_LIST_HEAD(&card->dai_link_list);
card->num_dai_links = 0;
INIT_LIST_HEAD(&card->rtd_list);
card->num_rtd = 0;
INIT_LIST_HEAD(&card->dapm_dirty);
INIT_LIST_HEAD(&card->dobj_list);
card->instantiated = 0;
mutex_init(&card->mutex);
mutex_init(&card->dapm_mutex);
ret = snd_soc_instantiate_card(card);
if (ret != 0)
return ret;
/* deactivate pins to sleep state */
list_for_each_entry(rtd, &card->rtd_list, list) {
struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
int j;
for (j = 0; j < rtd->num_codecs; j++) {
struct snd_soc_dai *codec_dai = rtd->codec_dais[j];
if (!codec_dai->active)
pinctrl_pm_select_sleep_state(codec_dai->dev);
}
if (!cpu_dai->active)
pinctrl_pm_select_sleep_state(cpu_dai->dev);
}
return ret;
}
snd_soc_instantiate_card会遍历每一对dai_link，进行codec、platform、dai的绑定工作，下只是代码的部分选节，详细的代码请直接参考完整的代码树。
/* bind DAIs */
for (i = 0; i < card->num_links; i++) {
ret = soc_bind_dai_link(card, &card->dai_link[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。
snd_soc_instantiate_card接着初始化Codec的寄存器缓存，然后调用标准的alsa函数创建声卡实例：
/* 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);
...
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);
然后，依次调用各个子结构的probe函数：
/* initialise the sound card only once */
if (card->probe) {
ret = card->probe(card);
if (ret < 0)
goto card_probe_error;
}
-----
/* probe all DAI links on this card */
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
",
ret);
goto probe_dai_err;
}
}
}
在上面的soc_probe_link_dais()函数中做了比较多的事情，把他展开继续讨论：
static int soc_probe_link_dais(struct snd_soc_card *card,
struct snd_soc_pcm_runtime *rtd, int order)
{
struct snd_soc_dai_link *dai_link = rtd->dai_link;
struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
int i, ret;
dev_dbg(card->dev, "ASoC: probe %s dai link %d late %d
",
card->name, rtd->num, order);
/* set default power off timeout */
rtd->pmdown_time = pmdown_time;
ret = soc_probe_dai(cpu_dai, order);
if (ret)
return ret;
/* probe the CODEC DAI */
for (i = 0; i < rtd->num_codecs; i++) {
ret = soc_probe_dai(rtd->codec_dais[i], order);
if (ret)
return ret;
}
/* complete DAI probe during last probe */
if (order != SND_SOC_COMP_ORDER_LAST)
return 0;
/* do machine specific initialization */
if (dai_link->init) {
ret = dai_link->init(rtd);
if (ret < 0) {
dev_err(card->dev, "ASoC: failed to init %s: %d
",
dai_link->name, ret);
return ret;
}
}
if (dai_link->dai_fmt)
snd_soc_runtime_set_dai_fmt(rtd, dai_link->dai_fmt);
ret = soc_post_component_init(rtd, dai_link->name);
if (ret)
return ret;
#ifdef CONFIG_DEBUG_FS
/* add DPCM sysfs entries */
if (dai_link->dynamic)
soc_dpcm_debugfs_add(rtd);
#endif
if (cpu_dai->driver->compress_new) {
/*create compress_device"*/
ret = cpu_dai->driver->compress_new(rtd, rtd->num);
if (ret < 0) {
dev_err(card->dev, "ASoC: can t create compress %s
",
dai_link->stream_name);
return ret;
}
} else {
if (!dai_link->params) {
/* create the pcm */
ret = soc_new_pcm(rtd, rtd->num);
if (ret < 0) {
dev_err(card->dev, "ASoC: can t create pcm %s :%d
",
dai_link->stream_name, ret);
return ret;
}
ret = soc_link_dai_pcm_new(&cpu_dai, 1, rtd);
if (ret < 0)
return ret;
ret = soc_link_dai_pcm_new(rtd->codec_dais,
rtd->num_codecs, rtd);
if (ret < 0)
return ret;
} else {
INIT_DELAYED_WORK(&rtd->delayed_work,
codec2codec_close_delayed_work);
/* link the DAI widgets */
ret = soc_link_dai_widgets(card, dai_link, rtd);
if (ret)
return ret;
}
}
return 0;
}
该函数除了挨个调用了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。目前把该函数的部分代码也贴出来：
- sound/soc/soc-pcm.c
/* create a new pcm */
int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
{
struct snd_soc_platform *platform = rtd->platform;
struct snd_soc_dai *codec_dai;
struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
struct snd_soc_component *component;
struct snd_soc_rtdcom_list *rtdcom;
struct snd_pcm *pcm;
char new_name[64];
int ret = 0, playback = 0, capture = 0;
int i;
if (rtd->dai_link->dynamic || rtd->dai_link->no_pcm) {
playback = rtd->dai_link->dpcm_playback;
capture = rtd->dai_link->dpcm_capture;
} else {
for (i = 0; i < rtd->num_codecs; i++) {
codec_dai = rtd->codec_dais[i];
if (codec_dai->driver->playback.channels_min)
playback = 1;
if (codec_dai->driver->capture.channels_min)
capture = 1;
}
capture = capture && cpu_dai->driver->capture.channels_min;
playback = playback && cpu_dai->driver->playback.channels_min;
}
if (rtd->dai_link->playback_only) {
playback = 1;
capture = 0;
}
if (rtd->dai_link->capture_only) {
playback = 0;
capture = 1;
}
/* create the PCM */
if (rtd->dai_link->no_pcm) {
snprintf(new_name, sizeof(new_name), "(%s)",
rtd->dai_link->stream_name);
ret = snd_pcm_new_internal(rtd->card->snd_card, new_name, num,
playback, capture, &pcm);
} else {
if (rtd->dai_link->dynamic)
snprintf(new_name, sizeof(new_name), "%s (*)",
rtd->dai_link->stream_name);
else
snprintf(new_name, sizeof(new_name), "%s %s-%d",
rtd->dai_link->stream_name,
(rtd->num_codecs > 1) ?
"multicodec" : rtd->codec_dai->name, num);
ret = snd_pcm_new(rtd->card->snd_card, new_name, num, playback,
capture, &pcm);
}
if (ret < 0) {
dev_err(rtd->card->dev, "ASoC: can t create pcm for %s
",
rtd->dai_link->name);
return ret;
}
dev_dbg(rtd->card->dev, "ASoC: registered pcm #%d %s
",num, new_name);
/* DAPM dai link stream work */
INIT_DELAYED_WORK(&rtd->delayed_work, close_delayed_work);
pcm->nonatomic = rtd->dai_link->nonatomic;
rtd->pcm = pcm;
pcm->private_data = rtd;
if (rtd->dai_link->no_pcm) {
if (playback)
pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].substream->private_data = rtd;
if (capture)
pcm->streams[SNDRV_PCM_STREAM_CAPTURE].substream->private_data = rtd;
goto out;
}
/* ASoC PCM operations */
if (rtd->dai_link->dynamic) {
rtd->ops.open = dpcm_fe_dai_open;
rtd->ops.hw_params = dpcm_fe_dai_hw_params;
rtd->ops.prepare = dpcm_fe_dai_prepare;
rtd->ops.trigger = dpcm_fe_dai_trigger;
rtd->ops.hw_free = dpcm_fe_dai_hw_free;
rtd->ops.close = dpcm_fe_dai_close;
rtd->ops.pointer = soc_pcm_pointer;
rtd->ops.ioctl = soc_pcm_ioctl;
} else {
rtd->ops.open = soc_pcm_open;
rtd->ops.hw_params = soc_pcm_hw_params;
rtd->ops.prepare = soc_pcm_prepare;
rtd->ops.trigger = soc_pcm_trigger;
rtd->ops.hw_free = soc_pcm_hw_free;
rtd->ops.close = soc_pcm_close;
rtd->ops.pointer = soc_pcm_pointer;
rtd->ops.ioctl = soc_pcm_ioctl;
}
for_each_rtdcom(rtd, rtdcom) {
const struct snd_pcm_ops *ops = rtdcom->component->driver->ops;
if (!ops)
continue;
if (ops->ack)
rtd->ops.ack = soc_rtdcom_ack;
if (ops->copy_user)
rtd->ops.copy_user = soc_rtdcom_copy_user;
if (ops->copy_kernel)
rtd->ops.copy_kernel = soc_rtdcom_copy_kernel;
if (ops->fill_silence)
rtd->ops.fill_silence = soc_rtdcom_fill_silence;
if (ops->page)
rtd->ops.page = soc_rtdcom_page;
if (ops->mmap)
rtd->ops.mmap = soc_rtdcom_mmap;
}
/* overwrite */
if (platform && platform->driver->ops) {
rtd->ops.ack = platform->driver->ops->ack;
rtd->ops.copy_user = platform->driver->ops->copy_user;
rtd->ops.copy_kernel = platform->driver->ops->copy_kernel;
rtd->ops.fill_silence = platform->driver->ops->fill_silence;
rtd->ops.page = platform->driver->ops->page;
rtd->ops.mmap = platform->driver->ops->mmap;
}
if (playback)
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &rtd->ops);
if (capture)
snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &rtd->ops);
for_each_rtdcom(rtd, rtdcom) {
component = rtdcom->component;
if (!component->pcm_new)
continue;
ret = component->pcm_new(component, rtd);
if (ret < 0) {
dev_err(component->dev,
"ASoC: pcm constructor failed: %d
",
ret);
return ret;
}
}
pcm->private_free = soc_pcm_private_free;
out:
dev_info(rtd->card->dev, "%s <-> %s mapping ok
",
(rtd->num_codecs > 1) ? "multicodec" : rtd->codec_dai->name,
cpu_dai->name);
return ret;
}
该函数第一初始化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。
回到snd_soc_instantiate_card函数，完成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，最后则是调用标准alsa驱动的声卡注册函数对声卡进行注册:
- sound/soc/soc-core.c
if (card->late_probe) {
ret = card->late_probe(card);
if (ret < 0) {
dev_err(card->dev, "ASoC: %s late_probe() failed: %d
",
card->name, ret);
goto probe_aux_dev_err;
}
}
snd_soc_dapm_new_widgets(card);
ret = snd_card_register(card->snd_card);
if (ret < 0) {
dev_err(card->dev, "ASoC: failed to register soundcard %d
",
ret);
goto probe_aux_dev_err;
}
至此，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明：
- 基于3.0内核 soc_probe序列图
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