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378 lines
9.2 KiB
378 lines
9.2 KiB
// SPDX-License-Identifier: GPL-2.0+ |
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/* |
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* sgp40.c - Support for Sensirion SGP40 Gas Sensor |
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* |
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* Copyright (C) 2021 Andreas Klinger <[email protected]> |
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* |
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* I2C slave address: 0x59 |
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* |
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* Datasheet can be found here: |
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* https://www.sensirion.com/file/datasheet_sgp40 |
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* |
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* There are two functionalities supported: |
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* |
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* 1) read raw logarithmic resistance value from sensor |
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* --> useful to pass it to the algorithm of the sensor vendor for |
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* measuring deteriorations and improvements of air quality. |
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* |
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* 2) calculate an estimated absolute voc index (0 - 500 index points) for |
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* measuring the air quality. |
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* For this purpose the value of the resistance for which the voc index |
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* will be 250 can be set up using calibbias. |
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* |
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* Compensation values of relative humidity and temperature can be set up |
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* by writing to the out values of temp and humidityrelative. |
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*/ |
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#include <linux/delay.h> |
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#include <linux/crc8.h> |
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#include <linux/module.h> |
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#include <linux/mutex.h> |
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#include <linux/i2c.h> |
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#include <linux/iio/iio.h> |
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/* |
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* floating point calculation of voc is done as integer |
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* where numbers are multiplied by 1 << SGP40_CALC_POWER |
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*/ |
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#define SGP40_CALC_POWER 14 |
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#define SGP40_CRC8_POLYNOMIAL 0x31 |
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#define SGP40_CRC8_INIT 0xff |
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DECLARE_CRC8_TABLE(sgp40_crc8_table); |
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struct sgp40_data { |
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struct device *dev; |
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struct i2c_client *client; |
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int rht; |
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int temp; |
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int res_calibbias; |
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/* Prevent concurrent access to rht, tmp, calibbias */ |
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struct mutex lock; |
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}; |
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struct sgp40_tg_measure { |
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u8 command[2]; |
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__be16 rht_ticks; |
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u8 rht_crc; |
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__be16 temp_ticks; |
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u8 temp_crc; |
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} __packed; |
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struct sgp40_tg_result { |
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__be16 res_ticks; |
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u8 res_crc; |
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} __packed; |
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static const struct iio_chan_spec sgp40_channels[] = { |
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{ |
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.type = IIO_CONCENTRATION, |
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.channel2 = IIO_MOD_VOC, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), |
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}, |
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{ |
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.type = IIO_RESISTANCE, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | |
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BIT(IIO_CHAN_INFO_CALIBBIAS), |
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}, |
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{ |
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.type = IIO_TEMP, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), |
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.output = 1, |
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}, |
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{ |
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.type = IIO_HUMIDITYRELATIVE, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_RAW), |
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.output = 1, |
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}, |
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}; |
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/* |
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* taylor approximation of e^x: |
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* y = 1 + x + x^2 / 2 + x^3 / 6 + x^4 / 24 + ... + x^n / n! |
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* |
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* Because we are calculating x real value multiplied by 2^power we get |
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* an additional 2^power^n to divide for every element. For a reasonable |
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* precision this would overflow after a few iterations. Therefore we |
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* divide the x^n part whenever its about to overflow (xmax). |
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*/ |
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static u32 sgp40_exp(int exp, u32 power, u32 rounds) |
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{ |
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u32 x, y, xp; |
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u32 factorial, divider, xmax; |
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int sign = 1; |
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int i; |
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if (exp == 0) |
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return 1 << power; |
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else if (exp < 0) { |
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sign = -1; |
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exp *= -1; |
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} |
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xmax = 0x7FFFFFFF / exp; |
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x = exp; |
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xp = 1; |
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factorial = 1; |
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y = 1 << power; |
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divider = 0; |
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for (i = 1; i <= rounds; i++) { |
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xp *= x; |
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factorial *= i; |
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y += (xp >> divider) / factorial; |
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divider += power; |
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/* divide when next multiplication would overflow */ |
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if (xp >= xmax) { |
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xp >>= power; |
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divider -= power; |
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} |
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} |
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if (sign == -1) |
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return (1 << (power * 2)) / y; |
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else |
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return y; |
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} |
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static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc) |
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{ |
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int x; |
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u32 exp = 0; |
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/* we calculate as a multiple of 16384 (2^14) */ |
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mutex_lock(&data->lock); |
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x = ((int)resistance_raw - data->res_calibbias) * 106; |
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mutex_unlock(&data->lock); |
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/* voc = 500 / (1 + e^x) */ |
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exp = sgp40_exp(x, SGP40_CALC_POWER, 18); |
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*voc = 500 * ((1 << (SGP40_CALC_POWER * 2)) / ((1<<SGP40_CALC_POWER) + exp)); |
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dev_dbg(data->dev, "raw: %d res_calibbias: %d x: %d exp: %d voc: %d\n", |
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resistance_raw, data->res_calibbias, x, exp, *voc); |
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return 0; |
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} |
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static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance_raw) |
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{ |
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int ret; |
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struct i2c_client *client = data->client; |
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u32 ticks; |
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u16 ticks16; |
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u8 crc; |
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struct sgp40_tg_measure tg = {.command = {0x26, 0x0F}}; |
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struct sgp40_tg_result tgres; |
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mutex_lock(&data->lock); |
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ticks = (data->rht / 10) * 65535 / 10000; |
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ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between 0 .. 100 %rH */ |
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tg.rht_ticks = cpu_to_be16(ticks16); |
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tg.rht_crc = crc8(sgp40_crc8_table, (u8 *)&tg.rht_ticks, 2, SGP40_CRC8_INIT); |
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ticks = ((data->temp + 45000) / 10 ) * 65535 / 17500; |
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ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between -45 .. +130 °C */ |
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tg.temp_ticks = cpu_to_be16(ticks16); |
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tg.temp_crc = crc8(sgp40_crc8_table, (u8 *)&tg.temp_ticks, 2, SGP40_CRC8_INIT); |
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mutex_unlock(&data->lock); |
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ret = i2c_master_send(client, (const char *)&tg, sizeof(tg)); |
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if (ret != sizeof(tg)) { |
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dev_warn(data->dev, "i2c_master_send ret: %d sizeof: %zu\n", ret, sizeof(tg)); |
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return -EIO; |
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} |
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msleep(30); |
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ret = i2c_master_recv(client, (u8 *)&tgres, sizeof(tgres)); |
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if (ret < 0) |
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return ret; |
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if (ret != sizeof(tgres)) { |
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dev_warn(data->dev, "i2c_master_recv ret: %d sizeof: %zu\n", ret, sizeof(tgres)); |
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return -EIO; |
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} |
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crc = crc8(sgp40_crc8_table, (u8 *)&tgres.res_ticks, 2, SGP40_CRC8_INIT); |
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if (crc != tgres.res_crc) { |
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dev_err(data->dev, "CRC error while measure-raw\n"); |
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return -EIO; |
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} |
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*resistance_raw = be16_to_cpu(tgres.res_ticks); |
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return 0; |
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} |
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static int sgp40_read_raw(struct iio_dev *indio_dev, |
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struct iio_chan_spec const *chan, int *val, |
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int *val2, long mask) |
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{ |
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struct sgp40_data *data = iio_priv(indio_dev); |
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int ret, voc; |
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u16 resistance_raw; |
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switch (mask) { |
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case IIO_CHAN_INFO_RAW: |
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switch (chan->type) { |
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case IIO_RESISTANCE: |
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ret = sgp40_measure_resistance_raw(data, &resistance_raw); |
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if (ret) |
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return ret; |
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*val = resistance_raw; |
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return IIO_VAL_INT; |
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case IIO_TEMP: |
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mutex_lock(&data->lock); |
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*val = data->temp; |
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mutex_unlock(&data->lock); |
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return IIO_VAL_INT; |
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case IIO_HUMIDITYRELATIVE: |
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mutex_lock(&data->lock); |
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*val = data->rht; |
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mutex_unlock(&data->lock); |
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return IIO_VAL_INT; |
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default: |
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return -EINVAL; |
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} |
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case IIO_CHAN_INFO_PROCESSED: |
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ret = sgp40_measure_resistance_raw(data, &resistance_raw); |
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if (ret) |
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return ret; |
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ret = sgp40_calc_voc(data, resistance_raw, &voc); |
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if (ret) |
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return ret; |
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*val = voc / (1 << SGP40_CALC_POWER); |
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/* |
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* calculation should fit into integer, where: |
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* voc <= (500 * 2^SGP40_CALC_POWER) = 8192000 |
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* (with SGP40_CALC_POWER = 14) |
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*/ |
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*val2 = ((voc % (1 << SGP40_CALC_POWER)) * 244) / (1 << (SGP40_CALC_POWER - 12)); |
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dev_dbg(data->dev, "voc: %d val: %d.%06d\n", voc, *val, *val2); |
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return IIO_VAL_INT_PLUS_MICRO; |
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case IIO_CHAN_INFO_CALIBBIAS: |
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mutex_lock(&data->lock); |
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*val = data->res_calibbias; |
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mutex_unlock(&data->lock); |
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return IIO_VAL_INT; |
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default: |
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return -EINVAL; |
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} |
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} |
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static int sgp40_write_raw(struct iio_dev *indio_dev, |
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struct iio_chan_spec const *chan, int val, |
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int val2, long mask) |
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{ |
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struct sgp40_data *data = iio_priv(indio_dev); |
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switch (mask) { |
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case IIO_CHAN_INFO_RAW: |
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switch (chan->type) { |
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case IIO_TEMP: |
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if ((val < -45000) || (val > 130000)) |
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return -EINVAL; |
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mutex_lock(&data->lock); |
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data->temp = val; |
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mutex_unlock(&data->lock); |
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return 0; |
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case IIO_HUMIDITYRELATIVE: |
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if ((val < 0) || (val > 100000)) |
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return -EINVAL; |
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mutex_lock(&data->lock); |
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data->rht = val; |
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mutex_unlock(&data->lock); |
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return 0; |
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default: |
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return -EINVAL; |
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} |
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case IIO_CHAN_INFO_CALIBBIAS: |
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if ((val < 20000) || (val > 52768)) |
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return -EINVAL; |
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mutex_lock(&data->lock); |
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data->res_calibbias = val; |
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mutex_unlock(&data->lock); |
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return 0; |
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} |
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return -EINVAL; |
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} |
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static const struct iio_info sgp40_info = { |
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.read_raw = sgp40_read_raw, |
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.write_raw = sgp40_write_raw, |
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}; |
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static int sgp40_probe(struct i2c_client *client, |
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const struct i2c_device_id *id) |
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{ |
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struct device *dev = &client->dev; |
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struct iio_dev *indio_dev; |
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struct sgp40_data *data; |
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int ret; |
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indio_dev = devm_iio_device_alloc(dev, sizeof(*data)); |
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if (!indio_dev) |
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return -ENOMEM; |
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data = iio_priv(indio_dev); |
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data->client = client; |
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data->dev = dev; |
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crc8_populate_msb(sgp40_crc8_table, SGP40_CRC8_POLYNOMIAL); |
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mutex_init(&data->lock); |
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/* set default values */ |
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data->rht = 50000; /* 50 % */ |
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data->temp = 25000; /* 25 °C */ |
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data->res_calibbias = 30000; /* resistance raw value for voc index of 250 */ |
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indio_dev->info = &sgp40_info; |
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indio_dev->name = id->name; |
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indio_dev->modes = INDIO_DIRECT_MODE; |
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indio_dev->channels = sgp40_channels; |
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indio_dev->num_channels = ARRAY_SIZE(sgp40_channels); |
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ret = devm_iio_device_register(dev, indio_dev); |
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if (ret) |
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dev_err(dev, "failed to register iio device\n"); |
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return ret; |
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} |
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static const struct i2c_device_id sgp40_id[] = { |
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{ "sgp40" }, |
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{ } |
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}; |
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MODULE_DEVICE_TABLE(i2c, sgp40_id); |
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static const struct of_device_id sgp40_dt_ids[] = { |
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{ .compatible = "sensirion,sgp40" }, |
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{ } |
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}; |
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MODULE_DEVICE_TABLE(of, sgp40_dt_ids); |
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static struct i2c_driver sgp40_driver = { |
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.driver = { |
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.name = "sgp40", |
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.of_match_table = sgp40_dt_ids, |
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}, |
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.probe = sgp40_probe, |
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.id_table = sgp40_id, |
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}; |
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module_i2c_driver(sgp40_driver); |
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MODULE_AUTHOR("Andreas Klinger <[email protected]>"); |
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MODULE_DESCRIPTION("Sensirion SGP40 gas sensor"); |
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MODULE_LICENSE("GPL v2");
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