ASOC声卡驱动框架

硬件平台mini2440开发板(S3C2440+UDA1341)

linux版本:linux-3.4.99

ASoC--ALSA System on Chip ,是建立在标准ALSA驱动层上,为了更好地支持嵌入式处理器和移动设备中的音频Codec的一套软件体系。在ASoc出现之前,内核对于SoC中的音频已经有部分的支持,不过会有一些局限性:

通常,就像软件领域里的抽象和重用一样,嵌入式设备的音频系统可以被划分为板载硬件(Machine)、Soc(Platform)、Codec三大部分,如下图所示:

                                                                    


下面就3大部分分别看下相关代码

1.platform:在该开发板中,platform包含了DMA和IIS的实现。

    DMA:在/sound/soc/samsung/dma.c文件中,相关代码为:

static struct platform_driver asoc_dma_driver = {
	.driver = {
		.name = "samsung-audio",
		.owner = THIS_MODULE,
	},

	.probe = samsung_asoc_platform_probe,
	.remove = __devexit_p(samsung_asoc_platform_remove),
};

Static struct snd_soc_platform_driver samsung_asoc_platform = {
	.ops		= &dma_ops,
	.pcm_new	= dma_new,
	.pcm_free	= dma_free_dm_buffers,
};

static struct snd_pcm_ops dma_ops = {
	.open		= dma_open,
	.close		= dma_close,
	.ioctl		= snd_pcm_lib_ioctl,
	.hw_params	= dma_hw_params,
	.hw_free	= dma_hw_free,
	.prepare	= dma_prepare,
	.trigger	= dma_trigger,
	.pointer	= dma_pointer,
	.mmap		= dma_mmap,
};

        根据dev,drv驱动模型,查找“samsung-audio”在arch\arm\plat-samsung\devs.c文件中有相关dev的注册:

struct platform_device samsung_asoc_dma = {
	.name		= "samsung-audio",
	.id		= -1,
	.dev		= {
		.dma_mask		= &samsung_device_dma_mask,
		.coherent_dma_mask	= DMA_BIT_MASK(32),
	}
};

      从而调用DMA中的probe函数,即上述的相关代码。

IIS:在\sound\soc\samsung\S3c24xx-i2s.c中实现了相关代码:

static struct platform_driver s3c24xx_iis_driver = {
	.probe  = s3c24xx_iis_dev_probe,
	.remove = __devexit_p(s3c24xx_iis_dev_remove),
	.driver = {
		.name = "s3c24xx-iis",
		.owner = THIS_MODULE,
	},
};

static const struct snd_soc_dai_ops s3c24xx_i2s_dai_ops = {
	.trigger	= s3c24xx_i2s_trigger,
	.hw_params	= s3c24xx_i2s_hw_params,
	.set_fmt	= s3c24xx_i2s_set_fmt,
	.set_clkdiv	= s3c24xx_i2s_set_clkdiv,
	.set_sysclk	= s3c24xx_i2s_set_sysclk,
};

static struct snd_soc_dai_driver s3c24xx_i2s_dai = {
	.probe = s3c24xx_i2s_probe,
	.suspend = s3c24xx_i2s_suspend,
	.resume = s3c24xx_i2s_resume,
	.playback = {
		.channels_min = 2,
		.channels_max = 2,
		.rates = S3C24XX_I2S_RATES,
		.formats = SNDRV_PCM_FMTBIT_S8 | SNDRV_PCM_FMTBIT_S16_LE,},
	.capture = {
		.channels_min = 2,
		.channels_max = 2,
		.rates = S3C24XX_I2S_RATES,
		.formats = SNDRV_PCM_FMTBIT_S8 | SNDRV_PCM_FMTBIT_S16_LE,},
	.ops = &s3c24xx_i2s_dai_ops,
};

该文件中配置了播放,录音,及数据格式等参数,并且注册了XX_dai_ops结构体,对于dev的注册,也是在 arch\arm\plat-samsung\devs.c函数中实现。

struct platform_device s3c_device_iis = {
	.name		= "s3c24xx-iis",
	.id		= -1,
	.num_resources	= ARRAY_SIZE(s3c_iis_resource),
	.resource	= s3c_iis_resource,
	.dev		= {
		.dma_mask		= &samsung_device_dma_mask,
		.coherent_dma_mask	= DMA_BIT_MASK(32),
	}
};

2.codec:在codec部分涉及到具体的声卡芯片了,在mini2440开发板中,用了UDA1341芯片,故关注sound\soc\codecs\uda134x.c文件。

static struct platform_driver uda134x_codec_driver = {
	.driver = {
		.name = "uda134x-codec",
		.owner = THIS_MODULE,
	},
	.probe = uda134x_codec_probe,
	.remove = __devexit_p(uda134x_codec_remove),
};

static const struct snd_soc_dai_ops uda134x_dai_ops = {
	.startup	= uda134x_startup,
	.shutdown	= uda134x_shutdown,
	.hw_params	= uda134x_hw_params,
	.digital_mute	= uda134x_mute,
	.set_sysclk	= uda134x_set_dai_sysclk,
	.set_fmt	= uda134x_set_dai_fmt,
};

static struct snd_soc_dai_driver uda134x_dai = {
	.name = "uda134x-hifi",
	/* playback capabilities */
	.playback = {
		.stream_name = "Playback",
		.channels_min = 1,
		.channels_max = 2,
		.rates = UDA134X_RATES,
		.formats = UDA134X_FORMATS,
	},
	/* capture capabilities */
	.capture = {
		.stream_name = "Capture",
		.channels_min = 1,
		.channels_max = 2,
		.rates = UDA134X_RATES,
		.formats = UDA134X_FORMATS,
	},
	/* pcm operations */
	.ops = &uda134x_dai_ops,
};

static struct snd_soc_codec_driver soc_codec_dev_uda134x = {
	.probe =        uda134x_soc_probe,
	.remove =       uda134x_soc_remove,
	.suspend =      uda134x_soc_suspend,
	.resume =       uda134x_soc_resume,
	.reg_cache_size = sizeof(uda134x_reg),
	.reg_word_size = sizeof(u8),
	.reg_cache_default = uda134x_reg,
	.reg_cache_step = 1,
	.read = uda134x_read_reg_cache,
	.write = uda134x_write,
	.set_bias_level = uda134x_set_bias_level,
};

static int __devinit uda134x_codec_probe(struct platform_device *pdev)
{
	return snd_soc_register_codec(&pdev->dev,
			&soc_codec_dev_uda134x, &uda134x_dai, 1);
}

该文件包含了UDA1341芯片的驱动函数,如果要调用该文件中的probe函数,需要注册在板子的初始化中注册该声卡的dev,在mach-smdk2440.c中添加:

static struct platform_device uda1340_codec = {
		.name = "uda134x-codec",
		.id = -1,
};

machine:与自己板子相关的代码,因为在内核中能找到mini2440开发板类似的平台声卡,故可以直接拿来用。

                   sound\soc\samsung\s3c24xx_uda134x.c

static struct platform_driver s3c24xx_uda134x_driver = {
	.probe  = s3c24xx_uda134x_probe,
	.remove = s3c24xx_uda134x_remove,
	.driver = {
		.name = "s3c24xx_uda134x",
		.owner = THIS_MODULE,
	},
};

要使上述probe函数呗调用,需在mach-smdk2440.c中添加:

static struct platform_device smdk2440_audio = {
	.name		= "s3c24xx_uda134x",
	.id		= 0,
	.dev		= {
		.platform_data	= &smdk2440_audio_pins,
	},
};

s3c24xx_uda134x_snd_device = platform_device_alloc("soc-audio", -1);
	if (!s3c24xx_uda134x_snd_device) {
		printk(KERN_ERR "S3C24XX_UDA134X SoC Audio: "
		       "Unable to register\n");
		return -ENOMEM;
	}

	platform_set_drvdata(s3c24xx_uda134x_snd_device,
			     &snd_soc_s3c24xx_uda134x);
	platform_device_add_data(s3c24xx_uda134x_snd_device, &s3c24xx_uda134x, sizeof(s3c24xx_uda134x));
	ret = platform_device_add(s3c24xx_uda134x_snd_device);
	if (ret) {
		printk(KERN_ERR "S3C24XX_UDA134X SoC Audio: Unable to add\n");
		platform_device_put(s3c24xx_uda134x_snd_device);
	}

static struct snd_soc_ops s3c24xx_uda134x_ops = {
	.startup = s3c24xx_uda134x_startup,
	.shutdown = s3c24xx_uda134x_shutdown,
	.hw_params = s3c24xx_uda134x_hw_params,
};

static struct snd_soc_dai_link s3c24xx_uda134x_dai_link = {
	.name = "UDA134X",
	.stream_name = "UDA134X",
	.codec_name = "uda134x-codec",
	.codec_dai_name = "uda134x-hifi",
	.cpu_dai_name = "s3c24xx-iis",
	.ops = &s3c24xx_uda134x_ops,
	.platform_name	= "samsung-audio",
};

static struct snd_soc_card snd_soc_s3c24xx_uda134x = {
	.name = "S3C24XX_UDA134X",
	.owner = THIS_MODULE,
	.dai_link = &s3c24xx_uda134x_dai_link,
	.num_links = 1,
};

之后看到代码将machine和之前说的platform,codec关联起来。大概就构成了ASOC的框架。

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