alsa Machine、Platform和Codec 驱动实例源码解析（基于am335x）

学习alsa音频驱动过程，一定有了解ASoC被分为Machine、Platform和Codec三大部分。其中的Machine驱动负责Platform和Codec之间的耦合和设备或板子特定的代码。框架的资料网上比较多，具体实例确不多，以致于我看了好多资料，还不知源码中哪一部分属于machine驱动。希望能帮助初学的人

那么这三大部分结合到具体的单板，到底是如何初始化的呢，本文就以am335x为例一步一步解说

machine驱动，用于为目标板绑定正确的platform和codec驱动，完成这个任务的就在soc_bind_dai_link(struct snd_soc_card *card, int num)中，实际上就是将card->rtd的三个重要成员card->rtd->cpu_dai，card->rtd->codec，card->rtd->platform初始化

全文涉及的文有：

sound\soc\davinci\davinci-evm.c "soc-audio" 设备注册(alsa machine)
sound\soc\soc-core.c "soc-audio" 驱动注册(alsa machine)
sound\soc\davinci\davinci-pcm.c "davinci-pcm-audio" 驱动注册(alsa platform)
arch\arm\mach-omap2\devices.c "davinci-pcm-audio"设备注册 (alsa platform)
sound\soc\codecs\tlv320aic3x.c  i2c驱动注册(alsa codec)
arch\arm\mach-omap2\board-am335xevm.c i2c "tlv320aic3x-codec.1-001b"设备注册(alsa codec)
sound\soc\davinci\davinci-mcasp.c "davinci-mcasp" 驱动注册(alsa dai)
arch\arm\mach-omap2\devices.c "davinci-mcasp"设备注册(alsa dai)

 (1)  alsa的machine驱动

sound\soc\davinci\davinci-evm.c     
 

static struct snd_soc_dai_link am335x_evm_dai = {

         .name = "TLV320AIC3X",

         .stream_name = "AIC3X",

         .cpu_dai_name = "davinci-mcasp.0",//1->0

         .codec_dai_name = "tlv320aic3x-hifi",

         .codec_name = "tlv320aic3x-codec.1-001b",//2->1

         .platform_name = "davinci-pcm-audio",

         .init = evm_aic3x_init,

         .ops = &evm_ops,

};

static struct snd_soc_card am335x_snd_soc_card = {

         .name = "AM335X EVM",

         .dai_link = &am335x_evm_dai,

         .num_links = 1,

};

evm_init(){

  evm_snd_dev_data = &am335x_snd_soc_card;

  evm_snd_device = platform_device_alloc("soc-audio", index);

  platform_set_drvdata(evm_snd_device, evm_snd_dev_data);

  platform_device_add(evm_snd_device);

}

   

这将触发"soc-audio"平台设备驱动的probe函数，这在soc-core.c中

sound\soc\soc-core.c                                                                 

static struct platform_driver soc_driver = {

         .driver = {

                   .name = "soc-audio",

                   .owner = THIS_MODULE,

                   .pm = &snd_soc_pm_ops,

         },

         .probe = soc_probe,

         .remove = soc_remove,

};

soc_probe(){

  snd_soc_register_card(am335x_snd_soc_card){

    card->rtd = kzalloc()

    snd_soc_instantiate_cards()

    snd_soc_instantiate_card()

      soc_bind_dai_link(){

      rtd->cpu_dai [find cpu_dai_name == davinci-mcasp.0]

      rtd->codec [find codec_name == tlv320aic3x-codec.1-001b]

      rtd->platform [find platform_name == davinci-pcm-audio]

  }

}

在soc_bind_dai_link找到合适的cpu_dai, codec, platform,具体查找过程看源码比较好理解，就是分别从dai_list ,codec_list，platform_list链表中找到名字相同的项，接下来就是理清这三个list是如何被add的就可以了

 (2) alsa的platform驱动 (platform_list)

从soc_bind_dai_link()中可以看出，一定有一个名为davinci-pcm-audio的alsa platform驱动，经过搜索snd_soc_register_platform()完成platform_list的add操作

 

sound\soc\davinci\davinci-pcm.c  davinci-pcm-audio驱动注册

static struct platform_driver davinci_pcm_driver = {

         .driver = {

                            .name = "davinci-pcm-audio",

                            .owner = THIS_MODULE,

         },

         .probe = davinci_soc_platform_probe,

         .remove = __devexit_p(davinci_soc_platform_remove),

};

static int __init snd_davinci_pcm_init(void)

{

         return platform_driver_register(&davinci_pcm_driver);

}

module_init(snd_davinci_pcm_init);

davinci_soc_platform_probe (){

   snd_soc_register_platform(){

           platform->name = fmt_single_name(dev, &platform->id);// 取出"davinci-pcm-audio",

      list_add(&platform->list, &platform_list);

      snd_soc_instantiate_cards();

   }

}

 

arch\arm\mach-omap2\devices.c    davinci-pcm-audio设备注册

 

struct platform_device am33xx_pcm_device = {

         .name = "davinci-pcm-audio",

         .id = -1,

};

arch_initcall(omap2_init_devices);

omap2_init_devices(){

  am33xx_init_pcm(){

    platform_device_register(&am33xx_pcm_device);

  }

}

 

(3) alsa的codec驱动 (codec_list)

sound\soc\codecs\tlv320aic3x.c  i2c驱动注册

aic3x_modinit(){

         i2c_add_driver(&aic3x_i2c_driver);

       aic3x_i2c_probe(){

         ret = snd_soc_register_codec(&i2c->dev,&soc_codec_dev_aic3x, &aic3x_dai, 1){

         codec->name = fmt_single_name(dev, &codec->id);

         list_add(&codec->list, &codec_list);

         }

       }

}

arch\arm\mach-omap2\board-am335xevm.c i2c tlv320aic3x-codec.1-001b设备注册



static struct evm_dev_cfg evm_sk_dev_cfg[] = {

                  {i2c0_init, DEV_ON_BASEBOARD, PROFILE_ALL},

};

am335x_evm_init(){

  am335x_evm_setup(){

    setup_starterkit(){

      _configure_device(EVM_SK, evm_sk_dev_cfg, PROFILE_NONE);

    }

  }

}

static struct i2c_board_info __initdata am335x_i2c0_boardinfo[] = {

         {

                   I2C_BOARD_INFO("tlv320aic3x", 0x1b),

         },

};

static void i2c0_init(int evm_id, int profile)

{

  omap_register_i2c_bus(1, 100, am335x_i2c0_boardinfo,ARRAY_SIZE(am335x_i2c0_boardinfo));

}

(4) alsa的dai驱动 dai_list

sound\soc\davinci\davinci-mcasp.c  "davinci-mcasp" 驱动

static struct snd_soc_dai_driver davinci_mcasp_dai[] = {

         {

                   .name = "davinci-mcasp.0",

                   .playback = {

                            .channels_min = 2,

                            .channels_max = 2,

                            .rates = DAVINCI_MCASP_RATES,

                            .formats = DAVINCI_MCASP_PCM_FMTS,

                   },

                   .capture = {

                            .channels_min = 2,

                            .channels_max = 2,

                            .rates = DAVINCI_MCASP_RATES,

                            .formats = DAVINCI_MCASP_PCM_FMTS,

                   },

                   .ops = &davinci_mcasp_dai_ops,



         },



};



static struct platform_driver davinci_mcasp_driver = {

         .probe = davinci_mcasp_probe,

         .remove = davinci_mcasp_remove,

#ifdef CONFIG_PM

         .suspend = davinci_mcasp_suspend,

         .resume = davinci_mcasp_resume,

#endif

         .driver = {

                   .name = "davinci-mcasp",

                   .owner = THIS_MODULE,

         },

};

davinci_mcasp_probe(){

  snd_soc_register_dai(&pdev->dev, &davinci_mcasp_dai[pdata->op_mode]){

    dai->name = fmt_single_name(dev, &dai->id);

      list_add(&dai->list, &dai_list);

           snd_soc_instantiate_cards();

  }

}

arch\arm\mach-omap2\devices.c  "davinci-mcasp"设备

mcasp0_init(){

  am335x_register_mcasp(&am335x_evm_snd_data0, 0){

  char *dev_name = "davinci-mcasp";

  pdev = omap_device_build(dev_name, ctrl_nr, oh, pdata,

                            sizeof(struct snd_platform_data), NULL, 0, 0);

  }

}