Exyons4412音频驱动----初始化之寄存器读写流程（一）

内核加载驱动：

module_init(snd_soc_init);

 加载完成之后进入：snd_soc_init() 初始化函数

static int __init snd_soc_init(void)
{
#ifdef CONFIG_DEBUG_FS
	snd_soc_debugfs_root = debugfs_create_dir("asoc", NULL);
	if (IS_ERR(snd_soc_debugfs_root) || !snd_soc_debugfs_root) {
		printk(KERN_WARNING
		       "ASoC: Failed to create debugfs directory\n");
		snd_soc_debugfs_root = NULL;
	}

	if (!debugfs_create_file("codecs", 0444, snd_soc_debugfs_root, NULL,
				 &codec_list_fops))
		pr_warn("ASoC: Failed to create CODEC list debugfs file\n");

	if (!debugfs_create_file("dais", 0444, snd_soc_debugfs_root, NULL,
				 &dai_list_fops))
		pr_warn("ASoC: Failed to create DAI list debugfs file\n");

	if (!debugfs_create_file("platforms", 0444, snd_soc_debugfs_root, NULL,
				 &platform_list_fops))
		pr_warn("ASoC: Failed to create platform list debugfs file\n");
#endif

	snd_soc_util_init();

	return platform_driver_register(&soc_driver);
}

soc_driver原型如下:

/* ASoC platform driver */
static struct platform_driver soc_driver = {
	.driver		= {
		.name		= "soc-audio",
		.owner		= THIS_MODULE,
		.pm		= &snd_soc_pm_ops,
	},
	.probe		= soc_probe,
	.remove		= soc_remove,
};

在执行platform_driver_register(&soc_driver); 这条语句之后 进入 soc_probe

该函数原型如下：

/* probes a new socdev */
static int soc_probe(struct platform_device *pdev)
{
	struct snd_soc_card *card = platform_get_drvdata(pdev);
	int ret = 0;

	/*
	 * no card, so machine driver should be registering card
	 * we should not be here in that case so ret error
	 */
	if (!card)
		return -EINVAL;

	/* Bodge while we unpick instantiation */
	card->dev = &pdev->dev;

	ret = snd_soc_register_card(card);
	if (ret != 0) {
		dev_err(&pdev->dev, "Failed to register card\n");
		return ret;
	}

	return 0;
}

调用该函数之后执行：ret = snd_soc_register_card(card)->snd_soc_instantiate_cards();->snd_soc_instantiate_card(card);

->ret = snd_soc_init_codec_cache(codec, compress_type);->ret = snd_soc_cache_init(codec);

执行到ret = snd_soc_cache_init(codec);函数之后会做一些处理 ， 该函数原型如下

int snd_soc_cache_init(struct snd_soc_codec *codec)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(cache_types); ++i)
		if (cache_types[i].id == codec->compress_type)
			break;

	/* Fall back to flat compression */
	if (i == ARRAY_SIZE(cache_types)) {
		dev_warn(codec->dev, "Could not match compress type: %d\n",
			 codec->compress_type);
		i = 0;
	}

	mutex_init(&codec->cache_rw_mutex);
	codec->cache_ops = &cache_types[i];

	if (codec->cache_ops->init) {
		if (codec->cache_ops->name)
			dev_dbg(codec->dev, "Initializing %s cache for %s codec\n",
				codec->cache_ops->name, codec->name);
		return codec->cache_ops->init(codec);
	}
	return -ENOSYS;
}

codec->cache_ops = &cache_types[i];  这句就是赋初始值   cache_types的定义如下

static const struct snd_soc_cache_ops cache_types[] = {
	/* Flat *must* be the first entry for fallback */
	{
		.id = SND_SOC_FLAT_COMPRESSION,
		.name = "flat",
		.init = snd_soc_flat_cache_init,
		.exit = snd_soc_flat_cache_exit,
		.read = snd_soc_flat_cache_read,
		.write = snd_soc_flat_cache_write,
		.sync = snd_soc_flat_cache_sync
	},
#ifdef CONFIG_SND_SOC_CACHE_LZO
	{
		.id = SND_SOC_LZO_COMPRESSION,
		.name = "LZO",
		.init = snd_soc_lzo_cache_init,
		.exit = snd_soc_lzo_cache_exit,
		.read = snd_soc_lzo_cache_read,
		.write = snd_soc_lzo_cache_write,
		.sync = snd_soc_lzo_cache_sync
	},
#endif
	{
		.id = SND_SOC_RBTREE_COMPRESSION,
		.name = "rbtree",
		.init = snd_soc_rbtree_cache_init,
		.exit = snd_soc_rbtree_cache_exit,
		.read = snd_soc_rbtree_cache_read,
		.write = snd_soc_rbtree_cache_write,
		.sync = snd_soc_rbtree_cache_sync
	}
};

根据上下文， 我们使用的是SND_SOC_FLAT_COMPRESSION 这个

 这个结构体里面的函数 所有原型如下

init函数

static int snd_soc_flat_cache_init(struct snd_soc_codec *codec)
{
	const struct snd_soc_codec_driver *codec_drv;

	codec_drv = codec->driver;

	if (codec->reg_def_copy)
		codec->reg_cache = kmemdup(codec->reg_def_copy,
					   codec->reg_size, GFP_KERNEL);
	else
		codec->reg_cache = kzalloc(codec->reg_size, GFP_KERNEL);
	if (!codec->reg_cache)
		return -ENOMEM;

	return 0;
}

如果def_copy有初始值， 那么就赋值给reg_cache （寄存器缓存值)  这个函数主要是 给寄存器的cache赋初始值

read函数

static int snd_soc_flat_cache_read(struct snd_soc_codec *codec,
				   unsigned int reg, unsigned int *value)
{
	*value = snd_soc_get_cache_val(codec->reg_cache, reg,
				       codec->driver->reg_word_size);
	return 0;
}

static unsigned int snd_soc_get_cache_val(const void *base, unsigned int idx,
		unsigned int word_size)
{
	if (!base)
		return -1;

	switch (word_size) {
	case 1: {
		const u8 *cache = base;
		return cache[idx];
	}
	case 2: {
		const u16 *cache = base;
		return cache[idx];
	}
	default:
		BUG();
	}
	/* unreachable */
	return -1;
}

 从代码中可以看到， read函数，是直接从codec->reg_cache 中读取de ,  通过查找init的代码 得知 如果codec->reg_def_copy有值，那么 codec->reg_cache 是从codec->reg_def_copy拷贝来的， 不然codec->reg_cache的值默认为0

上面是soc_sound ,read的流程。

write函数

static int snd_soc_flat_cache_write(struct snd_soc_codec *codec,
				    unsigned int reg, unsigned int value)
{
	snd_soc_set_cache_val(codec->reg_cache, reg, value,
			      codec->driver->reg_word_size);
	return 0;
}

static bool snd_soc_set_cache_val(void *base, unsigned int idx,
				  unsigned int val, unsigned int word_size)
{
	switch (word_size) {
	case 1: {
		u8 *cache = base;
		if (cache[idx] == val)
			return true;
		cache[idx] = val;
		break;
	}
	case 2: {
		u16 *cache = base;
		if (cache[idx] == val)
			return true;
		cache[idx] = val;
		break;
	}
	default:
		BUG();
	}
	return false;
}

从代码中可以看到，read ,  write都是操作reg_cache缓存中都写数据 ，  具体往寄存器中写入数值 继续往下看

wm8960为例子 ， 写寄存器函数为：

unsigned int snd_soc_write(struct snd_soc_codec *codec,
			   unsigned int reg, unsigned int val)
{
	dev_printk(KERN_DEBUG,codec->dev, "write %x = %x\n", reg, val);
	trace_snd_soc_reg_write(codec, reg, val);
	return codec->write(codec, reg, val);
}

codec->write(codec, reg, val); 调用的是这个函数。

在wm8960.c的wm8960_i2c_probe->snd_soc_register_codec函数中有如下赋值：

	codec->write = codec_drv->write;
	codec->read = codec_drv->read;

所以如果找到了

codec->write 
 codec->read

这二个函数， 那么操作读写也能找到。   继续看

wm8960.c中  初始化执行wm8960_probe之后调用了一个函数ret = snd_soc_codec_set_cache_io(codec, 7, 9, wm8960->control_type); 该函数原型为

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 = io_types[i].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

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

	return 0;
}

代码中对write和read进行了赋值

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

 而io_types的原型如下

static struct {
	int addr_bits;
	int data_bits;
	int (*write)(struct snd_soc_codec *codec, unsigned int, unsigned int);
	unsigned int (*read)(struct snd_soc_codec *, unsigned int);
	unsigned int (*i2c_read)(struct snd_soc_codec *, unsigned int);
} io_types[] = {
	{
		.addr_bits = 4, .data_bits = 12,
		.write = snd_soc_4_12_write, .read = snd_soc_4_12_read,
	},
	{
		.addr_bits = 7, .data_bits = 9,
		.write = snd_soc_7_9_write, .read = snd_soc_7_9_read,
	},
	{
		.addr_bits = 8, .data_bits = 8,
		.write = snd_soc_8_8_write, .read = snd_soc_8_8_read,
		.i2c_read = snd_soc_8_8_read_i2c,
	},
	{
		.addr_bits = 8, .data_bits = 16,
		.write = snd_soc_8_16_write, .read = snd_soc_8_16_read,
		.i2c_read = snd_soc_8_16_read_i2c,
	},
	{
		.addr_bits = 16, .data_bits = 8,
		.write = snd_soc_16_8_write, .read = snd_soc_16_8_read,
		.i2c_read = snd_soc_16_8_read_i2c,
	},
	{
		.addr_bits = 16, .data_bits = 16,
		.write = snd_soc_16_16_write, .read = snd_soc_16_16_read,
		.i2c_read = snd_soc_16_16_read_i2c,
	},
};

通过ret = snd_soc_codec_set_cache_io(codec, 7, 9, wm8960->control_type); 这句话得知， 我们使用的是7,9

7_9的读写函数如下

static int snd_soc_7_9_write(struct snd_soc_codec *codec, unsigned int reg,
			     unsigned int value)
{
	u8 data[2];

	data[0] = (reg << 1) | ((value >> 8) & 0x0001);
	data[1] = value & 0x00ff;

	return do_hw_write(codec, reg, value, data, 2);
}

static int do_hw_write(struct snd_soc_codec *codec, unsigned int reg,
		       unsigned int value, const void *data, int len)
{
	int ret;

	if (!snd_soc_codec_volatile_register(codec, reg) &&
	    reg < codec->driver->reg_cache_size &&
	    !codec->cache_bypass) {
		ret = snd_soc_cache_write(codec, reg, value);
		if (ret < 0)
			return -1;
	}

	if (codec->cache_only) {
		codec->cache_sync = 1;
		return 0;
	}

	ret = codec->hw_write(codec->control_data, data, len);
	if (ret == len)
		return 0;
	if (ret < 0)
		return ret;
	else
		return -EIO;
}

int snd_soc_cache_write(struct snd_soc_codec *codec,
			unsigned int reg, unsigned int value)
{
	int ret;

	mutex_lock(&codec->cache_rw_mutex);

	if (codec->cache_ops && codec->cache_ops->write) {
		ret = codec->cache_ops->write(codec, reg, value);
		mutex_unlock(&codec->cache_rw_mutex);
		return ret;
	}

	mutex_unlock(&codec->cache_rw_mutex);
	return -ENOSYS;
}

可以看到， 写函数主要操作了二个部分， 一个是 ret = snd_soc_cache_write(codec, reg, value); 另一个是 ret = codec->hw_write(codec->control_data, data, len);

snd_soc_cache_write的原型如下

int snd_soc_cache_write(struct snd_soc_codec *codec,
			unsigned int reg, unsigned int value)
{
	int ret;

	mutex_lock(&codec->cache_rw_mutex);

	if (codec->cache_ops && codec->cache_ops->write) {
		ret = codec->cache_ops->write(codec, reg, value);
		mutex_unlock(&codec->cache_rw_mutex);
		return ret;
	}

	mutex_unlock(&codec->cache_rw_mutex);
	return -ENOSYS;
}

从代码可以看到 写缓存调用的是 ret = codec->cache_ops->write(codec, reg, value);  这个在上文中已经提到。 cache_ops->write的调用函数

ret = codec->hw_write(codec->control_data, data, len); 这个函数调用的原型在snd_soc_codec_set_cache_io函数中也有赋值

	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

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

我们使用的是I2C 所以执行i2c_master_send

int i2c_master_send(const struct i2c_client *client, const char *buf, int count)
{
	int ret;
	struct i2c_adapter *adap = client->adapter;
	struct i2c_msg msg;

	msg.addr = client->addr;
	msg.flags = client->flags & I2C_M_TEN;
	msg.len = count;
	msg.buf = (char *)buf;

	ret = i2c_transfer(adap, &msg, 1);

	/* If everything went ok (i.e. 1 msg transmitted), return #bytes
	   transmitted, else error code. */
	return (ret == 1) ? count : ret;
}

以上就吧数据写进寄存器里面去了。

还有一个问题没交代清楚， 就是codec->reg_def_copy 的数值， 在wm8960.c中赋值的。

  在wm8960.c中   i2c初始化 wm8960_i2c_probe函数中调用了

  
 ret = snd_soc_register_codec(&i2c->dev, &soc_codec_dev_wm8960, &wm8960_dai, 1);

该函数中有一段代码

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)
{

...

	/* allocate CODEC register cache */
	if (codec_drv->reg_cache_size && codec_drv->reg_word_size) {
		reg_size = codec_drv->reg_cache_size * codec_drv->reg_word_size;
		codec->reg_size = reg_size;
		/* it is necessary to make a copy of the default register cache
		 * because in the case of using a compression type that requires
		 * the default register cache to be marked as __devinitconst the
		 * kernel might have freed the array by the time we initialize
		 * the cache.
		 */
		if (codec_drv->reg_cache_default) {
			codec->reg_def_copy = kmemdup(codec_drv->reg_cache_default,
						      reg_size, GFP_KERNEL);
			if (!codec->reg_def_copy) {
				ret = -ENOMEM;
				goto fail;
			}
		}
	}

如果codec_drv->reg_cache_default有值， 则cade->reg_def_copy就拷贝过来。　code->der是传进来的参数  为soc_codec_dev_wm8960

soc_codec_dev_wm8960的原型为

static struct snd_soc_codec_driver soc_codec_dev_wm8960 = {
	.probe =	wm8960_probe,
	.remove =	wm8960_remove,
	.suspend =	wm8960_suspend,
	.resume =	wm8960_resume,
	.set_bias_level = wm8960_set_bias_level,
	.reg_cache_size = ARRAY_SIZE(wm8960_reg),
	.reg_word_size = sizeof(u16),
	.reg_cache_default = wm8960_reg,
};

所以code_dev->reg_cache_default 指向的为wm8960_reg数组。

/*
 * wm8960 register cache
 * We can't read the WM8960 register space when we are
 * using 2 wire for device control, so we cache them instead.
 */
static const u16 wm8960_reg[WM8960_CACHEREGNUM] = {
	0x0097, 0x0097, 0x0000, 0x0000,
	0x0000, 0x0008, 0x0000, 0x000a,
	0x01c0, 0x0000, 0x00ff, 0x00ff,
	0x0000, 0x0000, 0x0000, 0x0000,
	0x0000, 0x007b, 0x0100, 0x0032,
	0x0000, 0x00c3, 0x00c3, 0x01c0,
	0x0000, 0x0000, 0x0000, 0x0000,
	0x0000, 0x0000, 0x0000, 0x0000,
	0x0100, 0x0100, 0x0050, 0x0050,
	0x0050, 0x0050, 0x0000, 0x0000,
	0x0000, 0x0000, 0x0040, 0x0000,
	0x0000, 0x0050, 0x0050, 0x0000,
	0x0002, 0x0037, 0x004d, 0x0080,
	0x0008, 0x0031, 0x0026, 0x00e9,
};

综上， soc在进行读的时候， 完全是操作wm8960这个数组，而在写的时候， 会先把数值写进数组， 在进行寄存器操作

新手：接触linux一个星期， 不知道分析的对不对。  希望大家多多指点。