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-rw-r--r--drivers/iio/chemical/sgp40.c378
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diff --git a/drivers/iio/chemical/sgp40.c b/drivers/iio/chemical/sgp40.c
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+// 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");
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.