linuxdebug/drivers/iio/chemical/sgp40.c

379 lines
9.2 KiB
C

// SPDX-License-Identifier: GPL-2.0+
/*
* sgp40.c - Support for Sensirion SGP40 Gas Sensor
*
* Copyright (C) 2021 Andreas Klinger <ak@it-klinger.de>
*
* 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 14
#define SGP40_CRC8_POLYNOMIAL 0x31
#define SGP40_CRC8_INIT 0xff
DECLARE_CRC8_TABLE(sgp40_crc8_table);
struct sgp40_data {
struct device *dev;
struct i2c_client *client;
int rht;
int temp;
int res_calibbias;
/* Prevent concurrent access to rht, tmp, calibbias */
struct mutex lock;
};
struct sgp40_tg_measure {
u8 command[2];
__be16 rht_ticks;
u8 rht_crc;
__be16 temp_ticks;
u8 temp_crc;
} __packed;
struct sgp40_tg_result {
__be16 res_ticks;
u8 res_crc;
} __packed;
static const struct iio_chan_spec sgp40_channels[] = {
{
.type = IIO_CONCENTRATION,
.channel2 = IIO_MOD_VOC,
.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
},
{
.type = IIO_RESISTANCE,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_CALIBBIAS),
},
{
.type = IIO_TEMP,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
.output = 1,
},
{
.type = IIO_HUMIDITYRELATIVE,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
.output = 1,
},
};
/*
* 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)
{
u32 x, y, xp;
u32 factorial, divider, xmax;
int sign = 1;
int i;
if (exp == 0)
return 1 << power;
else if (exp < 0) {
sign = -1;
exp *= -1;
}
xmax = 0x7FFFFFFF / exp;
x = exp;
xp = 1;
factorial = 1;
y = 1 << power;
divider = 0;
for (i = 1; i <= rounds; i++) {
xp *= x;
factorial *= i;
y += (xp >> divider) / factorial;
divider += power;
/* divide when next multiplication would overflow */
if (xp >= xmax) {
xp >>= power;
divider -= power;
}
}
if (sign == -1)
return (1 << (power * 2)) / y;
else
return y;
}
static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc)
{
int x;
u32 exp = 0;
/* we calculate as a multiple of 16384 (2^14) */
mutex_lock(&data->lock);
x = ((int)resistance_raw - data->res_calibbias) * 106;
mutex_unlock(&data->lock);
/* voc = 500 / (1 + e^x) */
exp = sgp40_exp(x, SGP40_CALC_POWER, 18);
*voc = 500 * ((1 << (SGP40_CALC_POWER * 2)) / ((1<<SGP40_CALC_POWER) + exp));
dev_dbg(data->dev, "raw: %d res_calibbias: %d x: %d exp: %d voc: %d\n",
resistance_raw, data->res_calibbias, x, exp, *voc);
return 0;
}
static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance_raw)
{
int ret;
struct i2c_client *client = data->client;
u32 ticks;
u16 ticks16;
u8 crc;
struct sgp40_tg_measure tg = {.command = {0x26, 0x0F}};
struct sgp40_tg_result tgres;
mutex_lock(&data->lock);
ticks = (data->rht / 10) * 65535 / 10000;
ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between 0 .. 100 %rH */
tg.rht_ticks = cpu_to_be16(ticks16);
tg.rht_crc = crc8(sgp40_crc8_table, (u8 *)&tg.rht_ticks, 2, SGP40_CRC8_INIT);
ticks = ((data->temp + 45000) / 10 ) * 65535 / 17500;
ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between -45 .. +130 °C */
tg.temp_ticks = cpu_to_be16(ticks16);
tg.temp_crc = crc8(sgp40_crc8_table, (u8 *)&tg.temp_ticks, 2, SGP40_CRC8_INIT);
mutex_unlock(&data->lock);
ret = i2c_master_send(client, (const char *)&tg, sizeof(tg));
if (ret != sizeof(tg)) {
dev_warn(data->dev, "i2c_master_send ret: %d sizeof: %zu\n", ret, sizeof(tg));
return -EIO;
}
msleep(30);
ret = i2c_master_recv(client, (u8 *)&tgres, sizeof(tgres));
if (ret < 0)
return ret;
if (ret != sizeof(tgres)) {
dev_warn(data->dev, "i2c_master_recv ret: %d sizeof: %zu\n", ret, sizeof(tgres));
return -EIO;
}
crc = crc8(sgp40_crc8_table, (u8 *)&tgres.res_ticks, 2, SGP40_CRC8_INIT);
if (crc != tgres.res_crc) {
dev_err(data->dev, "CRC error while measure-raw\n");
return -EIO;
}
*resistance_raw = be16_to_cpu(tgres.res_ticks);
return 0;
}
static int sgp40_read_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan, int *val,
int *val2, long mask)
{
struct sgp40_data *data = iio_priv(indio_dev);
int ret, voc;
u16 resistance_raw;
switch (mask) {
case IIO_CHAN_INFO_RAW:
switch (chan->type) {
case IIO_RESISTANCE:
ret = sgp40_measure_resistance_raw(data, &resistance_raw);
if (ret)
return ret;
*val = resistance_raw;
return IIO_VAL_INT;
case IIO_TEMP:
mutex_lock(&data->lock);
*val = data->temp;
mutex_unlock(&data->lock);
return IIO_VAL_INT;
case IIO_HUMIDITYRELATIVE:
mutex_lock(&data->lock);
*val = data->rht;
mutex_unlock(&data->lock);
return IIO_VAL_INT;
default:
return -EINVAL;
}
case IIO_CHAN_INFO_PROCESSED:
ret = sgp40_measure_resistance_raw(data, &resistance_raw);
if (ret)
return ret;
ret = sgp40_calc_voc(data, resistance_raw, &voc);
if (ret)
return ret;
*val = voc / (1 << SGP40_CALC_POWER);
/*
* calculation should fit into integer, where:
* voc <= (500 * 2^SGP40_CALC_POWER) = 8192000
* (with SGP40_CALC_POWER = 14)
*/
*val2 = ((voc % (1 << SGP40_CALC_POWER)) * 244) / (1 << (SGP40_CALC_POWER - 12));
dev_dbg(data->dev, "voc: %d val: %d.%06d\n", voc, *val, *val2);
return IIO_VAL_INT_PLUS_MICRO;
case IIO_CHAN_INFO_CALIBBIAS:
mutex_lock(&data->lock);
*val = data->res_calibbias;
mutex_unlock(&data->lock);
return IIO_VAL_INT;
default:
return -EINVAL;
}
}
static int sgp40_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan, int val,
int val2, long mask)
{
struct sgp40_data *data = iio_priv(indio_dev);
switch (mask) {
case IIO_CHAN_INFO_RAW:
switch (chan->type) {
case IIO_TEMP:
if ((val < -45000) || (val > 130000))
return -EINVAL;
mutex_lock(&data->lock);
data->temp = val;
mutex_unlock(&data->lock);
return 0;
case IIO_HUMIDITYRELATIVE:
if ((val < 0) || (val > 100000))
return -EINVAL;
mutex_lock(&data->lock);
data->rht = val;
mutex_unlock(&data->lock);
return 0;
default:
return -EINVAL;
}
case IIO_CHAN_INFO_CALIBBIAS:
if ((val < 20000) || (val > 52768))
return -EINVAL;
mutex_lock(&data->lock);
data->res_calibbias = val;
mutex_unlock(&data->lock);
return 0;
}
return -EINVAL;
}
static const struct iio_info sgp40_info = {
.read_raw = sgp40_read_raw,
.write_raw = sgp40_write_raw,
};
static int sgp40_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct device *dev = &client->dev;
struct iio_dev *indio_dev;
struct sgp40_data *data;
int ret;
indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
if (!indio_dev)
return -ENOMEM;
data = iio_priv(indio_dev);
data->client = client;
data->dev = dev;
crc8_populate_msb(sgp40_crc8_table, SGP40_CRC8_POLYNOMIAL);
mutex_init(&data->lock);
/* set default values */
data->rht = 50000; /* 50 % */
data->temp = 25000; /* 25 °C */
data->res_calibbias = 30000; /* resistance raw value for voc index of 250 */
indio_dev->info = &sgp40_info;
indio_dev->name = id->name;
indio_dev->modes = INDIO_DIRECT_MODE;
indio_dev->channels = sgp40_channels;
indio_dev->num_channels = ARRAY_SIZE(sgp40_channels);
ret = devm_iio_device_register(dev, indio_dev);
if (ret)
dev_err(dev, "failed to register iio device\n");
return ret;
}
static const struct i2c_device_id sgp40_id[] = {
{ "sgp40" },
{ }
};
MODULE_DEVICE_TABLE(i2c, sgp40_id);
static const struct of_device_id sgp40_dt_ids[] = {
{ .compatible = "sensirion,sgp40" },
{ }
};
MODULE_DEVICE_TABLE(of, sgp40_dt_ids);
static struct i2c_driver sgp40_driver = {
.driver = {
.name = "sgp40",
.of_match_table = sgp40_dt_ids,
},
.probe = sgp40_probe,
.id_table = sgp40_id,
};
module_i2c_driver(sgp40_driver);
MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
MODULE_DESCRIPTION("Sensirion SGP40 gas sensor");
MODULE_LICENSE("GPL v2");