linux/drivers/iio/chemical/sgp40.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * sgp40.c - Support for Sensirion SGP40 Gas Sensor
 *
 * Copyright (C) 2021 Andreas Klinger <[email protected]>
 *
 * I2C slave address: 0x59
 *
 * Datasheet can be found here:
 * https://www.sensirion.com/file/datasheet_sgp40
 *
 * There are two functionalities supported:
 *
 * 1) read raw logarithmic resistance value from sensor
 *    --> useful to pass it to the algorithm of the sensor vendor for
 *    measuring deteriorations and improvements of air quality.
 *
 * 2) calculate an estimated absolute voc index (0 - 500 index points) for
 *    measuring the air quality.
 *    For this purpose the value of the resistance for which the voc index
 *    will be 250 can be set up using calibbias.
 *
 * Compensation values of relative humidity and temperature can be set up
 * by writing to the out values of temp and humidityrelative.
 */

#include <linux/delay.h>
#include <linux/crc8.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/i2c.h>
#include <linux/iio/iio.h>

/*
 * floating point calculation of voc is done as integer
 * where numbers are multiplied by 1 << SGP40_CALC_POWER
 */
#define SGP40_CALC_POWER …

#define SGP40_CRC8_POLYNOMIAL …
#define SGP40_CRC8_INIT …

DECLARE_CRC8_TABLE(sgp40_crc8_table);

struct sgp40_data { … };

struct sgp40_tg_measure { … } __packed;

struct sgp40_tg_result { … } __packed;

static const struct iio_chan_spec sgp40_channels[] = …;

/*
 * taylor approximation of e^x:
 * y = 1 + x + x^2 / 2 + x^3 / 6 + x^4 / 24 + ... + x^n / n!
 *
 * Because we are calculating x real value multiplied by 2^power we get
 * an additional 2^power^n to divide for every element. For a reasonable
 * precision this would overflow after a few iterations. Therefore we
 * divide the x^n part whenever its about to overflow (xmax).
 */

static u32 sgp40_exp(int exp, u32 power, u32 rounds)
{ … }

static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc)
{ … }

static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance_raw)
{ … }

static int sgp40_read_raw(struct iio_dev *indio_dev,
			struct iio_chan_spec const *chan, int *val,
			int *val2, long mask)
{ … }

static int sgp40_write_raw(struct iio_dev *indio_dev,
			struct iio_chan_spec const *chan, int val,
			int val2, long mask)
{ … }

static const struct iio_info sgp40_info = …;

static int sgp40_probe(struct i2c_client *client)
{ … }

static const struct i2c_device_id sgp40_id[] = …;

MODULE_DEVICE_TABLE(i2c, sgp40_id);

static const struct of_device_id sgp40_dt_ids[] = …;

MODULE_DEVICE_TABLE(of, sgp40_dt_ids);

static struct i2c_driver sgp40_driver = …;
module_i2c_driver(…) …;

MODULE_AUTHOR(…) …;
MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;