https://blog.csdn.net/zyuanyun/article/details/59170418
ALSA Asoc框架如下图：
Asoc分为machine,platform,codec三大模块。关于machine，platform,codec的介绍参考自这里http://blog.csdn.net/droidphone/article/details/7165482
Machine 是指某一款机器，可以是某款设备，某款开发板，又或者是某款智能手机，由此可以看出Machine几乎是不可重用的，每个Machine上的硬件实现可能都不一样，CPU不一样，Codec不一样，音频的输入、输出设备也不一样，Machine为CPU、Codec、输入输出设备提供了一个载体。Platform 一般是指某一个SoC平台，比如pxaxxx,s3cxxxx,omapxxx等等，与音频相关的通常包含该SoC中的时钟、DMA、I2S、PCM等等，只要指定了SoC，那么我们可以认为它会有一个对应的Platform，它只与SoC相关，与Machine无关，这样我们就可以把Platform抽象出来，使得同一款SoC不用做任何的改动，就可以用在不同的Machine中。实际上，把Platform认为是某个SoC更好理解。Codec 字面上的意思就是编解码器，Codec里面包含了I2S接口、D/A、A/D、Mixer、PA（功放），通常包含多种输入（Mic、Line-in、I2S、PCM）和多个输出（耳机、喇叭、听筒，Line-out），Codec和Platform一样，是可重用的部件，同一个Codec可以被不同的Machine使用。嵌入式Codec通常通过I2C对内部的寄存器进行控制。对应的会有machine, platform,codec driver。
Machine driver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。
platform driver,它包含了该SoC平台的音频DMA和音频接口的配置和控制（I2S，PCM，AC97等等）；它也不能包含任何与板子或机器相关的代码。
Codec driver,ASoC中的一个重要设计原则就是要求Codec驱动是平台无关的，它包含了一些音频的控件（Controls），音频接口，DAMP（动态音频电源管理）的定义和某些Codec IO功能。为了保证硬件无关性，任何特定于平台和机器的代码都要移到Platform和Machine驱动中。所有的Codec驱动都要提供以下特性：
Codec DAI 和 PCM的配置信息；Codec的IO控制方式（I2C，SPI等）；Mixer和其他的音频控件；Codec的ALSA音频操作接口；也可以提供以下功能：
DAPM描述信息；DAPM事件处理程序；DAC数字静音控制从数据结构看来，snd_soc_card代表着Machine驱动，snd_soc_platform则代表着Platform驱动，snd_soc_codec和soc_codec_device则代表了Codec驱动，而snd_soc_dai_link则负责连接Platform和Codec。
snd_soc_dai是snd_soc_platform和snd_soc_codec的数字音频接口,snd_soc_codec的dai为codec_dai,snd_soc_platform的dai为cpu_dai,snd_pcm是snd_soc_card实例化后注册的声卡类型.
下面以smdk_wm8580为例，看看再Asoc框架下的ALSA driver的编写。
static struct snd_soc_dai_link smdk_dai[] = {//snd_soc_dai_link中，指定了Platform、Codec、codec_dai、cpu_dai的名字 [PRI_PLAYBACK] = { /* Primary Playback i/f */ .name = "WM8580 PAIF RX", .stream_name = "Playback", .cpu_dai_name = "samsung-i2s.0", .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.0", .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, }, [SEC_PLAYBACK] = { /* Sec_Fifo Playback i/f */ .name = "Sec_FIFO TX", .stream_name = "Playback", .cpu_dai_name = "samsung-i2s-sec", .codec_dai_name = "wm8580-hifi-playback", .platform_name = "samsung-i2s-sec", .codec_name = "wm8580.0-001b", .dai_fmt = SMDK_DAI_FMT, .ops = &smdk_ops, }, };
static struct snd_soc_card smdk = { .name = "SMDK-I2S", .owner = THIS_MODULE, .dai_link = smdk_dai, .num_links = 2,
.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), };
static struct platform_device *smdk_snd_device;
static int __init smdk_audio_init(void) { int ret; char *str;
if (machine_is_smdkc100() || machine_is_smdkv210() || machine_is_smdkc110()) { smdk.num_links = 3; } else if (machine_is_smdk6410()) { str = (char *)smdk_dai[PRI_PLAYBACK].cpu_dai_name; str[strlen(str) - 1] = '2'; str = (char *)smdk_dai[PRI_CAPTURE].cpu_dai_name; str[strlen(str) - 1] = '2'; }
smdk_snd_device = platform_device_alloc("soc-audio", -1);//创建platform device,device 名字为soc-audio if (!smdk_snd_device) return -ENOMEM;
platform_set_drvdata(smdk_snd_device, &smdk);//将platform devcie的drvdata设置成snd_soc_card类型的smdk ret = platform_device_add(smdk_snd_device);//将platform device 加到platform bus中。
if (ret) platform_device_put(smdk_snd_device);
return ret; } module_init(smdk_audio_init);
static void __exit smdk_audio_exit(void) { platform_device_unregister(smdk_snd_device); } module_exit(smdk_audio_exit);
上述代码主要是在init时，创建一个名字为soc-audio 的platform device, 并将platform device的drvdata设置成snd_soc_card类型的实例，最后将platform device 注册到platform bus中，注册过程主要在platform_device_add中，在前面介绍platform device 注册过程时，如果platform bus上有名字为soc-audio的driver,则调用driver的probe函数。
名字为soc-audio的driver定义在soc-core.c中，
static struct platform_driver soc_driver = { .driver = { .name = "soc-audio",//名字与上面的platform device相同。 .pm = &snd_soc_pm_ops, }, .probe = soc_probe, .remove = soc_remove, };
static int __init snd_soc_init(void) { snd_soc_debugfs_init(); snd_soc_util_init();
return platform_driver_register(&soc_driver);//注册platform driver:soc_driver. } module_init(snd_soc_init);
调用platform driver的 probe 函数。
static int soc_probe(struct platform_device *pdev) { struct snd_soc_card *card = platform_get_drvdata(pdev);//获取platform device的drvdata,这个实在创建platform device时赋值，即上面的smdk
/* * 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()\n", card->name);
/* Bodge while we unpick instantiation */ card->dev = &pdev->dev;
return snd_soc_register_card(card);//注册card. }
在snd_soc_register_card中，主要调用的是snd_soc_instantiate_card。
在snd_soc_instantiate_card中首先绑定DAIs
/* bind DAIs */ for (i = 0; i < card->num_links; i++) { ret = soc_bind_dai_link(card, &card->dai_link[i]);//绑定card的dai_link. if (ret != 0) goto base_error; }
在soc_bind_dai_link中，创建一个snd_soc_pcm_runtime的rtd,并将card的dai_link赋值rtd，初始化rtd结构。
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_dai **codec_dais; struct snd_soc_platform *platform; const char *platform_name; int i;
dev_dbg(card->dev, "ASoC: binding %s\n", dai_link->name);
if (soc_is_dai_link_bound(card, dai_link)) {//判断是否已经绑定 dev_dbg(card->dev, "ASoC: dai link %s already bound\n",dai_link->name); return 0; }
rtd = soc_new_pcm_runtime(card, dai_link);//创建runtime. if (!rtd) return -ENOMEM;
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_err(card->dev, "ASoC: CPU DAI %s not registered\n",dai_link->cpu_dai_name); goto _err_defer; }
rtd->num_codecs = dai_link->num_codecs;//codec数
/* 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; } }
/* Single codec links expect codec and codec_dai in runtime data */ rtd->codec_dai = codec_dais[0]; rtd->codec = rtd->codec_dai->codec;
/* 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(platform, &platform_list, list) { if (dai_link->platform_of_node) { if (platform->dev->of_node !=dai_link->platform_of_node) continue; } else { if (strcmp(platform->component.name, platform_name)) continue; }
rtd->platform = platform; } if (!rtd->platform) { dev_err(card->dev, "ASoC: platform %s not registered\n", dai_link->platform_name); goto _err_defer; }
soc_add_pcm_runtime(card, rtd);//将rtd加到card的rtd_list中 return 0;
_err_defer: soc_free_pcm_runtime(rtd); return -EPROBE_DEFER; }
在绑定了dai_link后，接着创建snd_card结构，即声卡。与soc_snd_card不同，snd_card是soc_snd_card的成员 。
ret = snd_card_new(card->dev, SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1, card->owner, 0, &card->snd_card);
接下来probe dai_link上的component:
/* probe all components used by 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_components(card, rtd, order);//probe所有rtd上的components,包括cpu_dai, codec_dai, platform上的components. if (ret < 0) { dev_err(card->dev,"ASoC: failed to instantiate card %d\n",ret); goto probe_dai_err; } } }
紧接着probe 所有dai_links.
/* 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);//probe dai_link if (ret < 0) { dev_err(card->dev,"ASoC: failed to instantiate card %d\n",ret); goto probe_dai_err; } } }
在soc_probe_link_dais中，主要操作如下：
ret = soc_probe_dai(cpu_dai, order);//调用cpu_dai driver的probe
/* probe the CODEC DAI */ for (i = 0; i < rtd->num_codecs; i++) { ret = soc_probe_dai(rtd->codec_dais[i], order);//调用codec dai driver的probe }
ret = soc_new_pcm(rtd, rtd->num);//创建rtd 的snd_pcm结构
/* 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);//创建pcm，在前面文章已经详细讲过这个函数。 } 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);//设置pcm的操作函数为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);//调用snd_soc_platform_driver的pcm_new函数。 if (ret < 0) { dev_err(platform->dev,"ASoC: pcm constructor failed: %d\n",ret); return ret; } }
pcm->private_free = platform->driver->pcm_free; out: dev_info(rtd->card->dev, "%s <-> %s mapping ok\n",(rtd->num_codecs > 1) ? "multicodec" : rtd->codec_dai->name,cpu_dai->name); return ret; }
以上就完成了soc_probe_link_dais.接着将card注册到bus上，完成声卡的实例化。
ret = snd_card_register(card->snd_card);//在前面文章已经详细讲过这个函数
完成snd_card_register后，soc_probe基本上完成了platform driver的初始化。
