1、IIO equipment

	IIO yes  Industrial I/O  Abbreviation , yes Linux The following subsystem is designed for industrial input and output . Mainly used for sensor equipment ,ADC/DAC equipment .

2、 Basic framework

/*  Device private data structure  */
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 The focus of the equipment is iio_info, There's a little detour here , stay iio_info Need to fill attrs and read_raw,attr Is used to provide custom attributes ,		
read_raw Used to read the properties provided by the framework .IIO The device has one by default name attribute , The value of this property is iio_dev Of name, Other 		
 Attributes of can be added by yourself .

3、read_raw matters needing attention

	 The return value of this parameter function is quite special ,
	0: There was no return , Even if filled val1 and val2, There will be no display .
	1: Without decimal point , Use only val2 Value .
	>= 2:6 Decimal places above ,val1 It's a fraction .2 Is after the decimal point 6 position ,3 It's the decimal point 8 position .