summaryrefslogtreecommitdiffstats
path: root/drivers/hwmon/sht21.c
blob: e23dbf287233a851657ecb6579c64d16a489d063 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/* Sensirion SHT21 humidity and temperature sensor driver
 *
 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
 *
 * Data sheet available at https://www.sensirion.com/file/datasheet_sht21
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/device.h>
#include <linux/jiffies.h>

/* I2C command bytes */
#define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
#define SHT21_READ_SNB_CMD1 0xFA
#define SHT21_READ_SNB_CMD2 0x0F
#define SHT21_READ_SNAC_CMD1 0xFC
#define SHT21_READ_SNAC_CMD2 0xC9

/**
 * struct sht21 - SHT21 device specific data
 * @client: I2C client device
 * @lock: mutex to protect measurement values
 * @last_update: time of last update (jiffies)
 * @temperature: cached temperature measurement value
 * @humidity: cached humidity measurement value
 * @valid: only 0 before first measurement is taken
 * @eic: cached electronic identification code text
 */
struct sht21 {
	struct i2c_client *client;
	struct mutex lock;
	unsigned long last_update;
	int temperature;
	int humidity;
	bool valid;
	char eic[18];
};

/**
 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
 * milli celsius
 * @ticks: temperature ticks value received from sensor
 */
static inline int sht21_temp_ticks_to_millicelsius(int ticks)
{
	ticks &= ~0x0003; /* clear status bits */
	/*
	 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
	 * optimized for integer fixed point (3 digits) arithmetic
	 */
	return ((21965 * ticks) >> 13) - 46850;
}

/**
 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
 * one-thousandths of a percent relative humidity
 * @ticks: humidity ticks value received from sensor
 */
static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
{
	ticks &= ~0x0003; /* clear status bits */
	/*
	 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
	 * optimized for integer fixed point (3 digits) arithmetic
	 */
	return ((15625 * ticks) >> 13) - 6000;
}

/**
 * sht21_update_measurements() - get updated measurements from device
 * @dev: device
 *
 * Returns 0 on success, else negative errno.
 */
static int sht21_update_measurements(struct device *dev)
{
	int ret = 0;
	struct sht21 *sht21 = dev_get_drvdata(dev);
	struct i2c_client *client = sht21->client;

	mutex_lock(&sht21->lock);
	/*
	 * Data sheet 2.4:
	 * SHT2x should not be active for more than 10% of the time - e.g.
	 * maximum two measurements per second at 12bit accuracy shall be made.
	 */
	if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
		ret = i2c_smbus_read_word_swapped(client,
						  SHT21_TRIG_T_MEASUREMENT_HM);
		if (ret < 0)
			goto out;
		sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
		ret = i2c_smbus_read_word_swapped(client,
						  SHT21_TRIG_RH_MEASUREMENT_HM);
		if (ret < 0)
			goto out;
		sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
		sht21->last_update = jiffies;
		sht21->valid = true;
	}
out:
	mutex_unlock(&sht21->lock);

	return ret >= 0 ? 0 : ret;
}

/**
 * sht21_show_temperature() - show temperature measurement value in sysfs
 * @dev: device
 * @attr: device attribute
 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 *
 * Will be called on read access to temp1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht21_temperature_show(struct device *dev,
				      struct device_attribute *attr,
				      char *buf)
{
	struct sht21 *sht21 = dev_get_drvdata(dev);
	int ret;

	ret = sht21_update_measurements(dev);
	if (ret < 0)
		return ret;
	return sprintf(buf, "%d\n", sht21->temperature);
}

/**
 * sht21_show_humidity() - show humidity measurement value in sysfs
 * @dev: device
 * @attr: device attribute
 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 *
 * Will be called on read access to humidity1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht21_humidity_show(struct device *dev,
				   struct device_attribute *attr, char *buf)
{
	struct sht21 *sht21 = dev_get_drvdata(dev);
	int ret;

	ret = sht21_update_measurements(dev);
	if (ret < 0)
		return ret;
	return sprintf(buf, "%d\n", sht21->humidity);
}

static ssize_t eic_read(struct sht21 *sht21)
{
	struct i2c_client *client = sht21->client;
	u8 tx[2];
	u8 rx[8];
	u8 eic[8];
	struct i2c_msg msgs[2] = {
		{
			.addr = client->addr,
			.flags = 0,
			.len = 2,
			.buf = tx,
		},
		{
			.addr = client->addr,
			.flags = I2C_M_RD,
			.len = 8,
			.buf = rx,
		},
	};
	int ret;

	tx[0] = SHT21_READ_SNB_CMD1;
	tx[1] = SHT21_READ_SNB_CMD2;
	ret = i2c_transfer(client->adapter, msgs, 2);
	if (ret < 0)
		goto out;
	eic[2] = rx[0];
	eic[3] = rx[2];
	eic[4] = rx[4];
	eic[5] = rx[6];

	tx[0] = SHT21_READ_SNAC_CMD1;
	tx[1] = SHT21_READ_SNAC_CMD2;
	msgs[1].len = 6;
	ret = i2c_transfer(client->adapter, msgs, 2);
	if (ret < 0)
		goto out;
	eic[0] = rx[3];
	eic[1] = rx[4];
	eic[6] = rx[0];
	eic[7] = rx[1];

	ret = snprintf(sht21->eic, sizeof(sht21->eic),
		       "%02x%02x%02x%02x%02x%02x%02x%02x\n",
		       eic[0], eic[1], eic[2], eic[3],
		       eic[4], eic[5], eic[6], eic[7]);
out:
	if (ret < 0)
		sht21->eic[0] = 0;

	return ret;
}

/**
 * eic_show() - show Electronic Identification Code in sysfs
 * @dev: device
 * @attr: device attribute
 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
 *
 * Will be called on read access to eic sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t eic_show(struct device *dev,
	struct device_attribute *attr,
	char *buf)
{
	struct sht21 *sht21 = dev_get_drvdata(dev);
	int ret;

	ret = sizeof(sht21->eic) - 1;
	mutex_lock(&sht21->lock);
	if (!sht21->eic[0])
		ret = eic_read(sht21);
	if (ret > 0)
		memcpy(buf, sht21->eic, ret);
	mutex_unlock(&sht21->lock);
	return ret;
}

/* sysfs attributes */
static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);
static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);
static DEVICE_ATTR_RO(eic);

static struct attribute *sht21_attrs[] = {
	&sensor_dev_attr_temp1_input.dev_attr.attr,
	&sensor_dev_attr_humidity1_input.dev_attr.attr,
	&dev_attr_eic.attr,
	NULL
};

ATTRIBUTE_GROUPS(sht21);

static int sht21_probe(struct i2c_client *client)
{
	struct device *dev = &client->dev;
	struct device *hwmon_dev;
	struct sht21 *sht21;

	if (!i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_WORD_DATA)) {
		dev_err(&client->dev,
			"adapter does not support SMBus word transactions\n");
		return -ENODEV;
	}

	sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
	if (!sht21)
		return -ENOMEM;

	sht21->client = client;

	mutex_init(&sht21->lock);

	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
							   sht21, sht21_groups);
	return PTR_ERR_OR_ZERO(hwmon_dev);
}

/* Device ID table */
static const struct i2c_device_id sht21_id[] = {
	{ "sht21", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, sht21_id);

static struct i2c_driver sht21_driver = {
	.driver.name = "sht21",
	.probe_new   = sht21_probe,
	.id_table    = sht21_id,
};

module_i2c_driver(sht21_driver);

MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");