1 // SPDX-License-Identifier: GPL-2.0+
3  * sgp40.c - Support for Sensirion SGP40 Gas Sensor
5  * Copyright (C) 2021 Andreas Klinger <ak@it-klinger.de>
14  * 1) read raw logarithmic resistance value from sensor
15  *    --> useful to pass it to the algorithm of the sensor vendor for
19  * 2) calculate an estimated absolute voc index (in_concentration_input)
20  *    with 0 - 500 index points) for measuring the air quality.
21  *    For this purpose the value of the resistance for which the voc index
24  *    The voc index is calculated as:
25  *      x = (in_resistance_raw - in_resistance_calibbias) * 0.65
40  * floating point calculation of voc is done as integer
116                 sign = -1;  in sgp40_exp()
117                 exp *= -1;  in sgp40_exp()
135                         divider -= power;  in sgp40_exp()
139         if (sign == -1)  in sgp40_exp()
145 static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc)  in sgp40_calc_voc()  argument
151 	mutex_lock(&data->lock);  in sgp40_calc_voc()
152 	x = ((int)resistance_raw - data->res_calibbias) * 106;  in sgp40_calc_voc()
153 	mutex_unlock(&data->lock);  in sgp40_calc_voc()
155 	/* voc = 500 / (1 + e^x) */  in sgp40_calc_voc()
157 	*voc = 500 * ((1 << (SGP40_CALC_POWER * 2)) / ((1<<SGP40_CALC_POWER) + exp));  in sgp40_calc_voc()
159 	dev_dbg(data->dev, "raw: %d res_calibbias: %d x: %d exp: %d voc: %d\n",  in sgp40_calc_voc()
160 				resistance_raw, data->res_calibbias, x, exp, *voc);  in sgp40_calc_voc()
168 	struct i2c_client *client = data->client;  in sgp40_measure_resistance_raw()
175 	mutex_lock(&data->lock);  in sgp40_measure_resistance_raw()
177 	ticks = (data->rht / 10) * 65535 / 10000;  in sgp40_measure_resistance_raw()
182 	ticks = ((data->temp + 45000) / 10 ) * 65535 / 17500;  in sgp40_measure_resistance_raw()
183 	ticks16 = (u16)clamp(ticks, 0u, 65535u); /* clamp between -45 .. +130 °C */  in sgp40_measure_resistance_raw()
187 	mutex_unlock(&data->lock);  in sgp40_measure_resistance_raw()
191 		dev_warn(data->dev, "i2c_master_send ret: %d sizeof: %zu\n", ret, sizeof(tg));  in sgp40_measure_resistance_raw()
192 		return -EIO;  in sgp40_measure_resistance_raw()
200 		dev_warn(data->dev, "i2c_master_recv ret: %d sizeof: %zu\n", ret, sizeof(tgres));  in sgp40_measure_resistance_raw()
201 		return -EIO;  in sgp40_measure_resistance_raw()
206 		dev_err(data->dev, "CRC error while measure-raw\n");  in sgp40_measure_resistance_raw()
207 		return -EIO;  in sgp40_measure_resistance_raw()
220 	int ret, voc;  in sgp40_read_raw()  local
225 		switch (chan->type) {  in sgp40_read_raw()
234 			mutex_lock(&data->lock);  in sgp40_read_raw()
235 			*val = data->temp;  in sgp40_read_raw()
236 			mutex_unlock(&data->lock);  in sgp40_read_raw()
239 			mutex_lock(&data->lock);  in sgp40_read_raw()
240 			*val = data->rht;  in sgp40_read_raw()
241 			mutex_unlock(&data->lock);  in sgp40_read_raw()
244 			return -EINVAL;  in sgp40_read_raw()
251 		ret = sgp40_calc_voc(data, resistance_raw, &voc);  in sgp40_read_raw()
255 		*val = voc / (1 << SGP40_CALC_POWER);  in sgp40_read_raw()
258 		 * voc <= (500 * 2^SGP40_CALC_POWER) = 8192000  in sgp40_read_raw()
261 		*val2 = ((voc % (1 << SGP40_CALC_POWER)) * 244) / (1 << (SGP40_CALC_POWER - 12));  in sgp40_read_raw()
262 		dev_dbg(data->dev, "voc: %d val: %d.%06d\n", voc, *val, *val2);  in sgp40_read_raw()
265 		mutex_lock(&data->lock);  in sgp40_read_raw()
266 		*val = data->res_calibbias;  in sgp40_read_raw()
267 		mutex_unlock(&data->lock);  in sgp40_read_raw()
270 		return -EINVAL;  in sgp40_read_raw()
282 		switch (chan->type) {  in sgp40_write_raw()
284 			if ((val < -45000) || (val > 130000))  in sgp40_write_raw()
285 				return -EINVAL;  in sgp40_write_raw()
287 			mutex_lock(&data->lock);  in sgp40_write_raw()
288 			data->temp = val;  in sgp40_write_raw()
289 			mutex_unlock(&data->lock);  in sgp40_write_raw()
293 				return -EINVAL;  in sgp40_write_raw()
295 			mutex_lock(&data->lock);  in sgp40_write_raw()
296 			data->rht = val;  in sgp40_write_raw()
297 			mutex_unlock(&data->lock);  in sgp40_write_raw()
300 			return -EINVAL;  in sgp40_write_raw()
304 			return -EINVAL;  in sgp40_write_raw()
306 		mutex_lock(&data->lock);  in sgp40_write_raw()
307 		data->res_calibbias = val;  in sgp40_write_raw()
308 		mutex_unlock(&data->lock);  in sgp40_write_raw()
311 	return -EINVAL;  in sgp40_write_raw()
322 	struct device *dev = &client->dev;  in sgp40_probe()
329 		return -ENOMEM;  in sgp40_probe()
332 	data->client = client;  in sgp40_probe()
333 	data->dev = dev;  in sgp40_probe()
337 	mutex_init(&data->lock);  in sgp40_probe()
340 	data->rht = 50000;		/* 50 % */  in sgp40_probe()
341 	data->temp = 25000;		/* 25 °C */  in sgp40_probe()
342 	data->res_calibbias = 30000;	/* resistance raw value for voc index of 250 */  in sgp40_probe()
344 	indio_dev->info = &sgp40_info;  in sgp40_probe()
345 	indio_dev->name = id->name;  in sgp40_probe()
346 	indio_dev->modes = INDIO_DIRECT_MODE;  in sgp40_probe()
347 	indio_dev->channels = sgp40_channels;  in sgp40_probe()
348 	indio_dev->num_channels = ARRAY_SIZE(sgp40_channels);  in sgp40_probe()
381 MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
382 MODULE_DESCRIPTION("Sensirion SGP40 gas sensor");