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1/* Sensirion SHT21 humidity and temperature sensor driver
2 *
3 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
18 *
19 * Data sheet available (5/2010) at
20 * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
21 */
22
23#include <linux/module.h>
24#include <linux/init.h>
25#include <linux/slab.h>
26#include <linux/i2c.h>
27#include <linux/hwmon.h>
28#include <linux/hwmon-sysfs.h>
29#include <linux/err.h>
30#include <linux/mutex.h>
31#include <linux/device.h>
32#include <linux/jiffies.h>
33
34/* I2C command bytes */
35#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
36#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
37
38/**
39 * struct sht21 - SHT21 device specific data
40 * @hwmon_dev: device registered with hwmon
41 * @lock: mutex to protect measurement values
42 * @valid: only 0 before first measurement is taken
43 * @last_update: time of last update (jiffies)
44 * @temperature: cached temperature measurement value
45 * @humidity: cached humidity measurement value
46 */
47struct sht21 {
48 struct i2c_client *client;
49 struct mutex lock;
50 char valid;
51 unsigned long last_update;
52 int temperature;
53 int humidity;
54};
55
56/**
57 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
58 * milli celsius
59 * @ticks: temperature ticks value received from sensor
60 */
61static inline int sht21_temp_ticks_to_millicelsius(int ticks)
62{
63 ticks &= ~0x0003; /* clear status bits */
64 /*
65 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
66 * optimized for integer fixed point (3 digits) arithmetic
67 */
68 return ((21965 * ticks) >> 13) - 46850;
69}
70
71/**
72 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
73 * one-thousandths of a percent relative humidity
74 * @ticks: humidity ticks value received from sensor
75 */
76static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
77{
78 ticks &= ~0x0003; /* clear status bits */
79 /*
80 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
81 * optimized for integer fixed point (3 digits) arithmetic
82 */
83 return ((15625 * ticks) >> 13) - 6000;
84}
85
86/**
87 * sht21_update_measurements() - get updated measurements from device
88 * @dev: device
89 *
90 * Returns 0 on success, else negative errno.
91 */
92static int sht21_update_measurements(struct device *dev)
93{
94 int ret = 0;
95 struct sht21 *sht21 = dev_get_drvdata(dev);
96 struct i2c_client *client = sht21->client;
97
98 mutex_lock(&sht21->lock);
99 /*
100 * Data sheet 2.4:
101 * SHT2x should not be active for more than 10% of the time - e.g.
102 * maximum two measurements per second at 12bit accuracy shall be made.
103 */
104 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
105 ret = i2c_smbus_read_word_swapped(client,
106 SHT21_TRIG_T_MEASUREMENT_HM);
107 if (ret < 0)
108 goto out;
109 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
110 ret = i2c_smbus_read_word_swapped(client,
111 SHT21_TRIG_RH_MEASUREMENT_HM);
112 if (ret < 0)
113 goto out;
114 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
115 sht21->last_update = jiffies;
116 sht21->valid = 1;
117 }
118out:
119 mutex_unlock(&sht21->lock);
120
121 return ret >= 0 ? 0 : ret;
122}
123
124/**
125 * sht21_show_temperature() - show temperature measurement value in sysfs
126 * @dev: device
127 * @attr: device attribute
128 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
129 *
130 * Will be called on read access to temp1_input sysfs attribute.
131 * Returns number of bytes written into buffer, negative errno on error.
132 */
133static ssize_t sht21_show_temperature(struct device *dev,
134 struct device_attribute *attr,
135 char *buf)
136{
137 struct sht21 *sht21 = dev_get_drvdata(dev);
138 int ret;
139
140 ret = sht21_update_measurements(dev);
141 if (ret < 0)
142 return ret;
143 return sprintf(buf, "%d\n", sht21->temperature);
144}
145
146/**
147 * sht21_show_humidity() - show humidity measurement value in sysfs
148 * @dev: device
149 * @attr: device attribute
150 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
151 *
152 * Will be called on read access to humidity1_input sysfs attribute.
153 * Returns number of bytes written into buffer, negative errno on error.
154 */
155static ssize_t sht21_show_humidity(struct device *dev,
156 struct device_attribute *attr,
157 char *buf)
158{
159 struct sht21 *sht21 = dev_get_drvdata(dev);
160 int ret;
161
162 ret = sht21_update_measurements(dev);
163 if (ret < 0)
164 return ret;
165 return sprintf(buf, "%d\n", sht21->humidity);
166}
167
168/* sysfs attributes */
169static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
170 NULL, 0);
171static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
172 NULL, 0);
173
174static struct attribute *sht21_attrs[] = {
175 &sensor_dev_attr_temp1_input.dev_attr.attr,
176 &sensor_dev_attr_humidity1_input.dev_attr.attr,
177 NULL
178};
179
180ATTRIBUTE_GROUPS(sht21);
181
182static int sht21_probe(struct i2c_client *client,
183 const struct i2c_device_id *id)
184{
185 struct device *dev = &client->dev;
186 struct device *hwmon_dev;
187 struct sht21 *sht21;
188
189 if (!i2c_check_functionality(client->adapter,
190 I2C_FUNC_SMBUS_WORD_DATA)) {
191 dev_err(&client->dev,
192 "adapter does not support SMBus word transactions\n");
193 return -ENODEV;
194 }
195
196 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
197 if (!sht21)
198 return -ENOMEM;
199
200 sht21->client = client;
201
202 mutex_init(&sht21->lock);
203
204 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
205 sht21, sht21_groups);
206 return PTR_ERR_OR_ZERO(hwmon_dev);
207}
208
209/* Device ID table */
210static const struct i2c_device_id sht21_id[] = {
211 { "sht21", 0 },
212 { }
213};
214MODULE_DEVICE_TABLE(i2c, sht21_id);
215
216static struct i2c_driver sht21_driver = {
217 .driver.name = "sht21",
218 .probe = sht21_probe,
219 .id_table = sht21_id,
220};
221
222module_i2c_driver(sht21_driver);
223
224MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
225MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
226MODULE_LICENSE("GPL");
1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Sensirion SHT21 humidity and temperature sensor driver
3 *
4 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
5 *
6 * Data sheet available at https://www.sensirion.com/file/datasheet_sht21
7 */
8
9#include <linux/module.h>
10#include <linux/init.h>
11#include <linux/slab.h>
12#include <linux/i2c.h>
13#include <linux/hwmon.h>
14#include <linux/hwmon-sysfs.h>
15#include <linux/err.h>
16#include <linux/mutex.h>
17#include <linux/device.h>
18#include <linux/jiffies.h>
19
20/* I2C command bytes */
21#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
22#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
23#define SHT21_READ_SNB_CMD1 0xFA
24#define SHT21_READ_SNB_CMD2 0x0F
25#define SHT21_READ_SNAC_CMD1 0xFC
26#define SHT21_READ_SNAC_CMD2 0xC9
27
28/**
29 * struct sht21 - SHT21 device specific data
30 * @client: I2C client device
31 * @lock: mutex to protect measurement values
32 * @last_update: time of last update (jiffies)
33 * @temperature: cached temperature measurement value
34 * @humidity: cached humidity measurement value
35 * @valid: only 0 before first measurement is taken
36 * @eic: cached electronic identification code text
37 */
38struct sht21 {
39 struct i2c_client *client;
40 struct mutex lock;
41 unsigned long last_update;
42 int temperature;
43 int humidity;
44 bool valid;
45 char eic[18];
46};
47
48/**
49 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
50 * milli celsius
51 * @ticks: temperature ticks value received from sensor
52 */
53static inline int sht21_temp_ticks_to_millicelsius(int ticks)
54{
55 ticks &= ~0x0003; /* clear status bits */
56 /*
57 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
58 * optimized for integer fixed point (3 digits) arithmetic
59 */
60 return ((21965 * ticks) >> 13) - 46850;
61}
62
63/**
64 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
65 * one-thousandths of a percent relative humidity
66 * @ticks: humidity ticks value received from sensor
67 */
68static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
69{
70 ticks &= ~0x0003; /* clear status bits */
71 /*
72 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
73 * optimized for integer fixed point (3 digits) arithmetic
74 */
75 return ((15625 * ticks) >> 13) - 6000;
76}
77
78/**
79 * sht21_update_measurements() - get updated measurements from device
80 * @dev: device
81 *
82 * Returns 0 on success, else negative errno.
83 */
84static int sht21_update_measurements(struct device *dev)
85{
86 int ret = 0;
87 struct sht21 *sht21 = dev_get_drvdata(dev);
88 struct i2c_client *client = sht21->client;
89
90 mutex_lock(&sht21->lock);
91 /*
92 * Data sheet 2.4:
93 * SHT2x should not be active for more than 10% of the time - e.g.
94 * maximum two measurements per second at 12bit accuracy shall be made.
95 */
96 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
97 ret = i2c_smbus_read_word_swapped(client,
98 SHT21_TRIG_T_MEASUREMENT_HM);
99 if (ret < 0)
100 goto out;
101 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
102 ret = i2c_smbus_read_word_swapped(client,
103 SHT21_TRIG_RH_MEASUREMENT_HM);
104 if (ret < 0)
105 goto out;
106 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
107 sht21->last_update = jiffies;
108 sht21->valid = true;
109 }
110out:
111 mutex_unlock(&sht21->lock);
112
113 return ret >= 0 ? 0 : ret;
114}
115
116/**
117 * sht21_temperature_show() - show temperature measurement value in sysfs
118 * @dev: device
119 * @attr: device attribute
120 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
121 *
122 * Will be called on read access to temp1_input sysfs attribute.
123 * Returns number of bytes written into buffer, negative errno on error.
124 */
125static ssize_t sht21_temperature_show(struct device *dev,
126 struct device_attribute *attr,
127 char *buf)
128{
129 struct sht21 *sht21 = dev_get_drvdata(dev);
130 int ret;
131
132 ret = sht21_update_measurements(dev);
133 if (ret < 0)
134 return ret;
135 return sprintf(buf, "%d\n", sht21->temperature);
136}
137
138/**
139 * sht21_humidity_show() - show humidity measurement value in sysfs
140 * @dev: device
141 * @attr: device attribute
142 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
143 *
144 * Will be called on read access to humidity1_input sysfs attribute.
145 * Returns number of bytes written into buffer, negative errno on error.
146 */
147static ssize_t sht21_humidity_show(struct device *dev,
148 struct device_attribute *attr, char *buf)
149{
150 struct sht21 *sht21 = dev_get_drvdata(dev);
151 int ret;
152
153 ret = sht21_update_measurements(dev);
154 if (ret < 0)
155 return ret;
156 return sprintf(buf, "%d\n", sht21->humidity);
157}
158
159static ssize_t eic_read(struct sht21 *sht21)
160{
161 struct i2c_client *client = sht21->client;
162 u8 tx[2];
163 u8 rx[8];
164 u8 eic[8];
165 struct i2c_msg msgs[2] = {
166 {
167 .addr = client->addr,
168 .flags = 0,
169 .len = 2,
170 .buf = tx,
171 },
172 {
173 .addr = client->addr,
174 .flags = I2C_M_RD,
175 .len = 8,
176 .buf = rx,
177 },
178 };
179 int ret;
180
181 tx[0] = SHT21_READ_SNB_CMD1;
182 tx[1] = SHT21_READ_SNB_CMD2;
183 ret = i2c_transfer(client->adapter, msgs, 2);
184 if (ret < 0)
185 goto out;
186 eic[2] = rx[0];
187 eic[3] = rx[2];
188 eic[4] = rx[4];
189 eic[5] = rx[6];
190
191 tx[0] = SHT21_READ_SNAC_CMD1;
192 tx[1] = SHT21_READ_SNAC_CMD2;
193 msgs[1].len = 6;
194 ret = i2c_transfer(client->adapter, msgs, 2);
195 if (ret < 0)
196 goto out;
197 eic[0] = rx[3];
198 eic[1] = rx[4];
199 eic[6] = rx[0];
200 eic[7] = rx[1];
201
202 ret = snprintf(sht21->eic, sizeof(sht21->eic), "%8phN\n", eic);
203out:
204 if (ret < 0)
205 sht21->eic[0] = 0;
206
207 return ret;
208}
209
210/**
211 * eic_show() - show Electronic Identification Code in sysfs
212 * @dev: device
213 * @attr: device attribute
214 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
215 *
216 * Will be called on read access to eic sysfs attribute.
217 * Returns number of bytes written into buffer, negative errno on error.
218 */
219static ssize_t eic_show(struct device *dev,
220 struct device_attribute *attr,
221 char *buf)
222{
223 struct sht21 *sht21 = dev_get_drvdata(dev);
224 int ret;
225
226 ret = sizeof(sht21->eic) - 1;
227 mutex_lock(&sht21->lock);
228 if (!sht21->eic[0])
229 ret = eic_read(sht21);
230 if (ret > 0)
231 memcpy(buf, sht21->eic, ret);
232 mutex_unlock(&sht21->lock);
233 return ret;
234}
235
236/* sysfs attributes */
237static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);
238static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);
239static DEVICE_ATTR_RO(eic);
240
241static struct attribute *sht21_attrs[] = {
242 &sensor_dev_attr_temp1_input.dev_attr.attr,
243 &sensor_dev_attr_humidity1_input.dev_attr.attr,
244 &dev_attr_eic.attr,
245 NULL
246};
247
248ATTRIBUTE_GROUPS(sht21);
249
250static int sht21_probe(struct i2c_client *client)
251{
252 struct device *dev = &client->dev;
253 struct device *hwmon_dev;
254 struct sht21 *sht21;
255
256 if (!i2c_check_functionality(client->adapter,
257 I2C_FUNC_SMBUS_WORD_DATA)) {
258 dev_err(&client->dev,
259 "adapter does not support SMBus word transactions\n");
260 return -ENODEV;
261 }
262
263 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
264 if (!sht21)
265 return -ENOMEM;
266
267 sht21->client = client;
268
269 mutex_init(&sht21->lock);
270
271 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
272 sht21, sht21_groups);
273 return PTR_ERR_OR_ZERO(hwmon_dev);
274}
275
276/* Device ID table */
277static const struct i2c_device_id sht21_id[] = {
278 { "sht21" },
279 { }
280};
281MODULE_DEVICE_TABLE(i2c, sht21_id);
282
283static struct i2c_driver sht21_driver = {
284 .driver.name = "sht21",
285 .probe = sht21_probe,
286 .id_table = sht21_id,
287};
288
289module_i2c_driver(sht21_driver);
290
291MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
292MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
293MODULE_LICENSE("GPL");