summaryrefslogtreecommitdiffstats
path: root/drivers/iio/chemical/sgp40.c
blob: 8a56394cea4eb2c471ad2986e32f8e8424daf25b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
// 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");