machine简介
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,再次引用上一节的内容: 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
Linux内核版本:4.1.15
主芯片:IMX6ULL
codec芯片:WM8960
一、platform device
这里采用dts的方式表示device相关信息:
这里我们注意compatible属性,这里需要和driver中的compatible属性匹配。
其他属性含义如下:
compatible:非常重要,用于匹配相应的驱动文件,有两个属性值,在整个 linux 内核源码中搜索这两个属性值即可找到对应的驱动文件,这里找到的驱动文件为:sound/soc/fsl/imx-wm8960.c。
model:最终用户看到的此声卡名字,这里设置为“wm8960-audio”。
cpu-dai:CPU DAI(Digital Audio Interface)句柄,这里是 sai2 这个节点。
audio-codec:音频解码芯片句柄,也就是 WM8960 芯片,这里为“codec”这个节点。
asrc-controller:asrc 控制器,asrc 全称为 Asynchronous Sample Rate Converters,翻译过来就是异步采样频率转化器。
hp-det:耳机插入检测引脚设置,第一个参数为检测引脚,3 表示 JD3 为检测引脚。第二个参数设置检测电平,设置为 0 的时候,hp 检测到高电平表示耳机插入;设置为 1 的时候,hp 检测到高电平表示是喇叭,也就是耳机拔出了。
audio-routing:音频器件一系列的连接设置,每个条目都是一对字符串,第一个字符串是连接的 sink,第二个是连接的 source(源)。
二、platform driver
从上面的compatible属性我们就可以找到其machine驱动:
machine驱动路径为:sound\soc\fsl\imx-wm8960.c
此时驱动中的compatible属性与设备树中的compatible属性相匹配出发其probe函数:
static int imx_wm8960_probe(struct platform_device *pdev)
{
struct device_node *cpu_np, *codec_np = NULL;
struct platform_device *cpu_pdev;
struct imx_priv *priv = &card_priv;
struct i2c_client *codec_dev;
struct imx_wm8960_data *data;
struct platform_device *asrc_pdev = NULL;
struct device_node *asrc_np;
struct of_phandle_args args;
u32 width;
int ret;
priv->pdev = pdev;
/*从设备树中获取cpu-dai接口信息*/
cpu_np = of_parse_phandle(pdev->dev.of_node, "cpu-dai", 0);
if (!cpu_np) {
dev_err(&pdev->dev, "cpu dai phandle missing or invalid\n");
ret = -EINVAL;
goto fail;
}
/*从设备树中获取codec接口信息*/
codec_np = of_parse_phandle(pdev->dev.of_node, "audio-codec", 0);
if (!codec_np) {
dev_err(&pdev->dev, "phandle missing or invalid\n");
ret = -EINVAL;
goto fail;
}
······
/*申请私有数据结构体大小*/
data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
if (!data) {
ret = -ENOMEM;
goto fail;
}
······
data->card.dai_link = imx_wm8960_dai;
data->card.dev = &pdev->dev;
data->card.owner = THIS_MODULE;
/*设置声卡的名字*/
ret = snd_soc_of_parse_card_name(&data->card, "model");
if (ret)
goto fail;
data->card.dapm_widgets = imx_wm8960_dapm_widgets;
data->card.num_dapm_widgets = ARRAY_SIZE(imx_wm8960_dapm_widgets);
/*设置Audio的路由信息*/
ret = snd_soc_of_parse_audio_routing(&data->card, "audio-routing");
if (ret)
goto fail;
/*设置声卡后期需要初始化的内容*/
data->card.late_probe = imx_wm8960_late_probe;
/*设置私有数据*/
platform_set_drvdata(pdev, &data->card);
snd_soc_card_set_drvdata(&data->card, data);
/*注册声卡*/
ret = devm_snd_soc_register_card(&pdev->dev, &data->card);
if (ret) {
dev_err(&pdev->dev, "snd_soc_register_card failed (%d)\n", ret);
goto fail;
}
········
return ret;
}
前期获取的所有的信息都是为创建声卡做准备,接下来我们就看一下注册声卡的函数。devm_snd_soc_register_card最终调用snd_soc_register_card函数完成声卡的创建,传入的参数就是我们上面初始化的struct snd_soc_card *card。
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,
card->rtd = devm_kzalloc(card->dev,
sizeof(struct snd_soc_pcm_runtime) *
(card->num_links + card->num_aux_devs),
GFP_KERNEL);
if (card->rtd == NULL)
return -ENOMEM;
card->num_rtd = 0;
card->rtd_aux = &card->rtd[card->num_links];
for (i = 0; i < card->num_links; i++) {
card->rtd[i].card = card;
card->rtd[i].dai_link = &card->dai_link[i];
card->rtd[i].codec_dais = devm_kzalloc(card->dev,
sizeof(struct snd_soc_dai *) *
(card->rtd[i].dai_link->num_codecs),
GFP_KERNEL);
if (card->rtd[i].codec_dais == NULL)
return -ENOMEM;
}
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:
该函数遍历每一对dai_link,进行codec、platform、dai的绑定工作,以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, 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、DAlI、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Cara->taT(Sna_soe_puan_ruw a 址这个过程后,snd_soc_pcm_runtime: (card->rtd)中保存了本Machine中使用的Codec,DAl和Platform驱动的信息。
soc_probe_link_components依次回调各个probe: probe the CPU-side component、probe the CODEC-side components、probe the platform :
/* 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);
if (ret < 0) {
dev_err(card->dev,
"ASoC: failed to instantiate card %d\n",
ret);
goto probe_dai_err;
}
}
}
snd_soc_init_codec_cache函数接着初始化Codec的寄存器缓存,然后调用标准的alsa函数创建声卡实例:
/* initialize the register cache for each available codec */
list_for_each_entry(codec, &codec_list, list) {
if (codec->cache_init)
continue;
ret = snd_soc_init_codec_cache(codec);
if (ret < 0)
goto base_error;
}
/* 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 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);
if (ret < 0) {
dev_err(card->dev,
"ASoC: failed to instantiate card %d\n",
ret);
goto probe_dai_err;
}
}
}
在上面的soc_probe_dai_link()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, int num, int order)
{
struct snd_soc_dai_link *dai_link = &card->dai_link[num];
struct snd_soc_pcm_runtime *rtd = &card->rtd[num];
struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
int i, ret;
dev_dbg(card->dev, "ASoC: probe %s dai link %d late %d\n",
card->name, 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;
}
if (cpu_dai->driver->compress_dai) {
/*create compress_device"*/
ret = soc_new_compress(rtd, num);
if (ret < 0) {
dev_err(card->dev, "ASoC: can't create compress %s\n",
dai_link->stream_name);
return ret;
}
} else {
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 {
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;
}
首先回调cpu_dai与codec_dai的probe函数,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。现在把该函数的部分代码也贴出来:
/* 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_pcm *pcm;
char new_name[64];
int ret = 0, playback = 0, capture = 0;
int i;
/* 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\n",
rtd->dai_link->name);
return ret;
}
dev_dbg(rtd->card->dev, "ASoC: registered pcm #%d %s\n",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;
}
if (platform->driver->ops) {
rtd->ops.ack = platform->driver->ops->ack;
rtd->ops.copy = platform->driver->ops->copy;
rtd->ops.silence = platform->driver->ops->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);
if (platform->driver->pcm_new) {
ret = platform->driver->pcm_new(rtd);
if (ret < 0) {
dev_err(platform->dev,
"ASoC: pcm constructor failed: %d\n",
ret);
return ret;
}
}
pcm->private_free = platform->driver->pcm_free;
return ret;
}
该函数首先调用标准alsa驱动中的创建pcm的函数snd_pcm_new()创建声卡的pcm实例,然后初始化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,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的设置工作后,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snd_card_register对声卡进行注册:
if (card->late_probe) {
ret = card->late_probe(card);
if (ret < 0) {
dev_err(card->dev, "ASoC: %s late_probe() failed: %d\n",
card->name, ret);
goto probe_aux_dev_err;
}
}
snd_soc_dapm_new_widgets(card);
ret = snd_card_register(card->snd_card);
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示: