ALSA SOC在Linux3.1上的一些改进

2012已经到来,无论这个世界是否行将毁灭,在那之前的日子还得要继续。

Android迈进了4.0,相应的Linux内核也进入了3.x时代。之后的一个工作估计要将2.6.32的驱动移植到3.x上面来。因此趁现在有空,看看alsa在这方面有什么改动。


总的来说,架构大的改动是不大可能的。codec中几个关键结构体没有大的变化,如snd_soc_dai_ops、snd_soc_dai_driver(相当于2.6.32中的snd_soc_dai),倒是以前的snd_soc_codec_device重定义为snd_soc_codec_driver,这个算是最明显的。


注册用结构体-snd_soc_codec_driver


2.6.32:

/* codec device */
struct snd_soc_codec_device {
	int (*probe)(struct platform_device *pdev);
	int (*remove)(struct platform_device *pdev);
	int (*suspend)(struct platform_device *pdev, pm_message_t state);
	int (*resume)(struct platform_device *pdev);
};

3.1.1:
/* codec driver */
struct snd_soc_codec_driver {

	/* driver ops */
	int (*probe)(struct snd_soc_codec *);
	int (*remove)(struct snd_soc_codec *);
	int (*suspend)(struct snd_soc_codec *,
			pm_message_t state);
	int (*resume)(struct snd_soc_codec *);

	/* Default control and setup, added after probe() is run */
	const struct snd_kcontrol_new *controls;
	int num_controls;
	const struct snd_soc_dapm_widget *dapm_widgets;
	int num_dapm_widgets;
	const struct snd_soc_dapm_route *dapm_routes;
	int num_dapm_routes;

	/* codec wide operations */
	int (*set_sysclk)(struct snd_soc_codec *codec,
			  int clk_id, unsigned int freq, int dir);
	int (*set_pll)(struct snd_soc_codec *codec, int pll_id, int source,
		unsigned int freq_in, unsigned int freq_out);

	/* codec IO */
	unsigned int (*read)(struct snd_soc_codec *, unsigned int);
	int (*write)(struct snd_soc_codec *, unsigned int, unsigned int);
	int (*display_register)(struct snd_soc_codec *, char *,
				size_t, unsigned int);
	int (*volatile_register)(struct snd_soc_codec *, unsigned int);
	int (*readable_register)(struct snd_soc_codec *, unsigned int);
	int (*writable_register)(struct snd_soc_codec *, unsigned int);
	short reg_cache_size;
	short reg_cache_step;
	short reg_word_size;
	const void *reg_cache_default;
	short reg_access_size;
	const struct snd_soc_reg_access *reg_access_default;
	enum snd_soc_compress_type compress_type;

	/* codec bias level */
	int (*set_bias_level)(struct snd_soc_codec *,
			      enum snd_soc_bias_level level);

	void (*seq_notifier)(struct snd_soc_dapm_context *,
			     enum snd_soc_dapm_type, int);

	/* probe ordering - for components with runtime dependencies */
	int probe_order;
	int remove_order;
};

位于snd_soc_codec_driver中的一些codec IO成员函数和set_bias_level回调函数原来都放在另外一个结构体snd_soc_codec中,现在放置在这里了,这是根据源码结构调整的结果。事实真正需要设置的成员也不是很多,如下:

static struct snd_soc_codec_driver soc_codec_dev_wm9713 = {
	.probe = 	wm9713_soc_probe,
	.remove = 	wm9713_soc_remove,
	.suspend =	wm9713_soc_suspend,
	.resume = 	wm9713_soc_resume,
	.read = ac97_read,
	.write = ac97_write,
	.set_bias_level = wm9713_set_bias_level,
	.reg_cache_size = ARRAY_SIZE(wm9713_reg),
	.reg_word_size = sizeof(u16),
	.reg_cache_step = 2,
	.reg_cache_default = wm9713_reg,
	.dapm_widgets = wm9713_dapm_widgets,
	.num_dapm_widgets = ARRAY_SIZE(wm9713_dapm_widgets),
	.dapm_routes = wm9713_audio_map,
	.num_dapm_routes = ARRAY_SIZE(wm9713_audio_map),
};

probe、remove、suspend、resume相信不用累述了,volatile_register函数判断指定的寄存器是否volatile,reg_cache_size一般为寄存器数目,reg_word_size为寄存器的字长,reg_cache_default为寄存器默认值配置表。

而dapm_widgets、dapm_routes就比较“犀利”了。之前的dapm widgets和routes分别通过函数snd_soc_dapm_new_controls和snd_soc_dapm_add_routes来注册的(当然现在还保留这些接口),现在则可以填入到这个结构体,在soc-core里注册,省了不少功夫:

static int soc_probe_codec(struct snd_soc_card *card,
			   struct snd_soc_codec *codec)
{
	//...

	if (driver->dapm_widgets)
		snd_soc_dapm_new_controls(&codec->dapm, driver->dapm_widgets,
					  driver->num_dapm_widgets);

	//...

	if (driver->controls)
		snd_soc_add_controls(codec, driver->controls,
				     driver->num_controls);
	if (driver->dapm_routes)
		snd_soc_dapm_add_routes(&codec->dapm, driver->dapm_routes,
					driver->num_dapm_routes);
	//...
}


同时可看到dirver ops的函数参数有所不同了,以前是struct platform_device *pdev,现在改为struct snd_soc_codec *codec,这个与codec的注册函数snd_soc_register_codec和设备的drvdata有关,之后会逐一分析。


注册函数-snd_soc_register_codec


对于snd_soc_codec_driver,之前需要EXPORT_SYMBOL_GPL(soc_codec_dev_wm9713),然后在其他地方注册,现在不用那么麻烦了:

static __devinit int wm9713_probe(struct platform_device *pdev)
{
	return snd_soc_register_codec(&pdev->dev,
			&soc_codec_dev_wm9713, wm9713_dai, ARRAY_SIZE(wm9713_dai));
}

随后像普通的platform设备那样注册就行了。不再需要snd_soc_new_pcms注册pcm、snd_soc_init_card注册card。


snd_soc_register_codec函数原型:

int snd_soc_register_codec(struct device *dev,
		const struct snd_soc_codec_driver *codec_drv,
		struct snd_soc_dai_driver *dai_drv, int num_dai);
其中snd_soc_dai_driver与之前的snd_soc_dai类似,没有特别需要注意的地方,初始化如:
static struct snd_soc_dai_driver wm9713_dai[] = {
{
	.name = "wm9713-hifi",
	.ac97_control = 1,
	.playback = {
		.stream_name = "HiFi Playback",
		.channels_min = 1,
		.channels_max = 2,
		.rates = WM9713_RATES,
		.formats = SND_SOC_STD_AC97_FMTS,},
	.capture = {
		.stream_name = "HiFi Capture",
		.channels_min = 1,
		.channels_max = 2,
		.rates = WM9713_RATES,
		.formats = SND_SOC_STD_AC97_FMTS,},
	.ops = &wm9713_dai_ops_hifi,
	},
	//...
	//...
};


注:之前的snd_soc_dai也需要EXPORT_SYMBOL_GPL的,然后在其他地方注册的,现在改进了这点,减少了export的symbol,代码架构更加清晰可靠。


设备私有数据-drvdata


在ALSA之CODEC分析中有提到“开始看到socdev = platform_get_drvdata(pdev)这句不免有点疑惑,到底pdev是在哪里初始化好了?”,这个pdev就是drvdata。这个东东非常重要,它一般包含codec自定义的私有数据,如控制接口类型(I2C/SPI/AC97)、fll_in(FLL input frequency)、fll_out(FLL output frequency)等信息。因为每种codec可能定义的私有数据体不同,而Linux内核喜欢抽象,所以就产生了drvdata。

之前drvdata的来龙去脉是百转千回绕吊瓶的,而现在版本是比较直观的,且看分析:

static inline void snd_soc_codec_set_drvdata(struct snd_soc_codec *codec,
		void *data)
{
	dev_set_drvdata(codec->dev, data);
}

static inline void *snd_soc_codec_get_drvdata(struct snd_soc_codec *codec)
{
	return dev_get_drvdata(codec->dev);
}

soc.h里实现两个函数用于设置和获取drvdata。snd_soc_codec是codec驱动里最常使用的结构体,在各个操作函数均可以看到它的身影,所以选择它和drvdata联系起来。


使用方法如下:

static int wm9713_soc_probe(struct snd_soc_codec *codec)
{
	struct wm9713_priv *wm9713;
	int ret = 0, reg;

	wm9713 = kzalloc(sizeof(struct wm9713_priv), GFP_KERNEL);
	if (wm9713 == NULL)
		return -ENOMEM;
	snd_soc_codec_set_drvdata(codec, wm9713);
	
	//...
}

static int wm9713_soc_remove(struct snd_soc_codec *codec)
{
	struct wm9713_priv *wm9713 = snd_soc_codec_get_drvdata(codec);
	snd_soc_free_ac97_codec(codec);
	kfree(wm9713);
	return 0;
}


设置控制接口-snd_soc_codec_set_cache_io


这个函数在以前版本也有的,但是当时没有留意。现在发现这个函数很实用,只需要配置寄存器地址宽度、数据宽度、和控制接口类型,soc-io模块就自动会选择合适的控制接口函数。

/**
 * snd_soc_codec_set_cache_io: Set up standard I/O functions.
 *
 * @codec: CODEC to configure.
 * @addr_bits: Number of bits of register address data.
 * @data_bits: Number of bits of data per register.
 * @control: Control bus used.
 *
 * Register formats are frequently shared between many I2C and SPI
 * devices.  In order to promote code reuse the ASoC core provides
 * some standard implementations of CODEC read and write operations
 * which can be set up using this function.
 *
 * The caller is responsible for allocating and initialising the
 * actual cache.
 *
 * Note that at present this code cannot be used by CODECs with
 * volatile registers.
 */
int snd_soc_codec_set_cache_io(struct snd_soc_codec *codec,
			       int addr_bits, int data_bits,
			       enum snd_soc_control_type control)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(io_types); i++)
		if (io_types[i].addr_bits == addr_bits &&
		    io_types[i].data_bits == data_bits)
			break;
	if (i == ARRAY_SIZE(io_types)) {
		printk(KERN_ERR
		       "No I/O functions for %d bit address %d bit data\n",
		       addr_bits, data_bits);
		return -EINVAL;
	}

	codec->write = io_types[i].write;
	codec->read = hw_read;
	codec->bulk_write_raw = snd_soc_hw_bulk_write_raw;

	switch (control) {
	case SND_SOC_I2C:
#if defined(CONFIG_I2C) || (defined(CONFIG_I2C_MODULE) && defined(MODULE))
		codec->hw_write = (hw_write_t)i2c_master_send;
#endif
		if (io_types[i].i2c_read)
			codec->hw_read = io_types[i].i2c_read;

		codec->control_data = container_of(codec->dev,
						   struct i2c_client,
						   dev);
		break;

	case SND_SOC_SPI:
#ifdef CONFIG_SPI_MASTER
		codec->hw_write = do_spi_write;
#endif
		if (io_types[i].spi_read)
			codec->hw_read = io_types[i].spi_read;

		codec->control_data = container_of(codec->dev,
						   struct spi_device,
						   dev);
		break;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(snd_soc_codec_set_cache_io);

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