i2c client驱动之IIO设备驱动

1、IIO设备

	IIO是 Industrial I/O 的缩写，是Linux下为工业输入输出所设计的子系统。主要用于传感器设备，ADC/DAC设备。

2、基本框架

/* 设备私有数据结构 */
struct foobar_i2c_device_data {
	struct i2c_client *client;
	struct i2c_adapter *adap;
	struct iio_dev *indio;
};

static ssize_t type_show(struct device *dev, struct device_attribute *attr, char *buf)
{
    int ret;
    struct iio_dev *indio_dev = dev_to_iio_dev(dev);
    const struct iio_chan_spec *chan = indio_dev->channels;

    ret = sprintf(buf, "%d\n", chan->type);
    
    return ret;
}


static int i2c_foobar_iio_device_read_raw(struct iio_dev *indio_dev, 
            const struct iio_chan_spec *chan, int *val1, int *val2, long mask)
{
    struct foobar_i2c_device_data *i2c = iio_device_get_drvdata(indio_dev);

    dev_info(&i2c->adap->dev, "%d\n", chan->channel2);
    *val1 = chan->type;
    *val2 = chan->channel2;

    return 1;
}

static IIO_DEVICE_ATTR_RO(type, 0);

static struct attribute *i2c_foobar_attributes[] = {
    &iio_dev_attr_type.dev_attr.attr,
    NULL
};

static const struct attribute_group i2c_foobar_iio_device_attrs = {
    .attrs = i2c_foobar_attributes
};

static const struct iio_info foobar_iio_info = {
    .attrs = &i2c_foobar_iio_device_attrs,
    .read_raw = i2c_foobar_iio_device_read_raw,
};

static const struct iio_chan_spec i2c_iio_channels[] = {
    {
        .type = IIO_LIGHT,
        .modified = 1,
        .channel2 = IIO_MOD_LIGHT_IR,
        .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
    },
    {
        .type = IIO_PROXIMITY,
        .modified = 1,
        .channel2 = IIO_MOD_LIGHT_CLEAR,
        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
    }
};

static int iio_device_init(struct foobar_i2c_device_data *device)
{
	struct iio_dev *indio;
	int ret;

	indio = iio_device_alloc(&device->client->dev, sizeof(*indio));
	if (!indio) {
		ret = -ENOMEM;
		goto out;
	}

	indio->info = &foobar_iio_info;
	indio->channels = i2c_iio_channels;
	indio->num_channels = ARRAY_SIZE(i2c_iio_channels);
	indio->dev.parent = &device->client->dev;
	indio->name = "sensor name";

	ret = iio_device_register(indio);

	if (ret) {
		dev_err(&device->client->dev, "register iio device FAIL:%d\n", ret);
		iio_device_free(indio);
		goto out;
	}
	
	iio_device_set_drvdata(indio, device);
out:
	return ret;
}

static int foobar_i2c_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
	struct i2c_adapter *adap = client->adapter;
	struct foobar_i2c_device_data *device;
	int ret;
		
	device = kzalloc(sizeof(*device), GFP_KERNEL);
	if (!device)
		return -ENOMEM;

	device->client = client;
	device->adap = adap;
	
	ret = iio_device_init(device);

	if (ret) {
		dev_err(&adap->dev, "device init FAIL:%d\n", ret);
		kfree(device);
		return ret;
	}
	
	i2c_set_clientdata(client, device);
	
	return 0;
}

	IIO设备的重点是iio_info,这里有那么点绕，在iio_info中需要填充attrs和read_raw，attr是用于提供自定义属性，		
read_raw用于读取框架提供的属性读取。IIO设备默认有一个name属性，这个属性的值为iio_dev的name,其它		
的属性可以自己添加。

3、read_raw注意事项

	这个参数函数的返回值比较特别，
	0:没有任何返回，即使填充了val1和val2，也不会有任何显示。
	1:不带小数点，只使用val1的值。
	>= 2:6位以上小数点，val1为整数部分。2为小数点后6位，3为小数点8位。