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 */
38 struct 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 */
sht21_temp_ticks_to_millicelsius(int ticks)53 static 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 */
sht21_rh_ticks_to_per_cent_mille(int ticks)68 static 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 */
sht21_update_measurements(struct device * dev)84 static 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 }
110 out:
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 */
sht21_temperature_show(struct device * dev,struct device_attribute * attr,char * buf)125 static 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 */
sht21_humidity_show(struct device * dev,struct device_attribute * attr,char * buf)147 static 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
eic_read(struct sht21 * sht21)159 static 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),
203 "%02x%02x%02x%02x%02x%02x%02x%02x\n",
204 eic[0], eic[1], eic[2], eic[3],
205 eic[4], eic[5], eic[6], eic[7]);
206 out:
207 if (ret < 0)
208 sht21->eic[0] = 0;
209
210 return ret;
211 }
212
213 /**
214 * eic_show() - show Electronic Identification Code in sysfs
215 * @dev: device
216 * @attr: device attribute
217 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
218 *
219 * Will be called on read access to eic sysfs attribute.
220 * Returns number of bytes written into buffer, negative errno on error.
221 */
eic_show(struct device * dev,struct device_attribute * attr,char * buf)222 static ssize_t eic_show(struct device *dev,
223 struct device_attribute *attr,
224 char *buf)
225 {
226 struct sht21 *sht21 = dev_get_drvdata(dev);
227 int ret;
228
229 ret = sizeof(sht21->eic) - 1;
230 mutex_lock(&sht21->lock);
231 if (!sht21->eic[0])
232 ret = eic_read(sht21);
233 if (ret > 0)
234 memcpy(buf, sht21->eic, ret);
235 mutex_unlock(&sht21->lock);
236 return ret;
237 }
238
239 /* sysfs attributes */
240 static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);
241 static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);
242 static DEVICE_ATTR_RO(eic);
243
244 static struct attribute *sht21_attrs[] = {
245 &sensor_dev_attr_temp1_input.dev_attr.attr,
246 &sensor_dev_attr_humidity1_input.dev_attr.attr,
247 &dev_attr_eic.attr,
248 NULL
249 };
250
251 ATTRIBUTE_GROUPS(sht21);
252
sht21_probe(struct i2c_client * client)253 static int sht21_probe(struct i2c_client *client)
254 {
255 struct device *dev = &client->dev;
256 struct device *hwmon_dev;
257 struct sht21 *sht21;
258
259 if (!i2c_check_functionality(client->adapter,
260 I2C_FUNC_SMBUS_WORD_DATA)) {
261 dev_err(&client->dev,
262 "adapter does not support SMBus word transactions\n");
263 return -ENODEV;
264 }
265
266 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
267 if (!sht21)
268 return -ENOMEM;
269
270 sht21->client = client;
271
272 mutex_init(&sht21->lock);
273
274 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
275 sht21, sht21_groups);
276 return PTR_ERR_OR_ZERO(hwmon_dev);
277 }
278
279 /* Device ID table */
280 static const struct i2c_device_id sht21_id[] = {
281 { "sht21", 0 },
282 { }
283 };
284 MODULE_DEVICE_TABLE(i2c, sht21_id);
285
286 static struct i2c_driver sht21_driver = {
287 .driver.name = "sht21",
288 .probe = sht21_probe,
289 .id_table = sht21_id,
290 };
291
292 module_i2c_driver(sht21_driver);
293
294 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
295 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
296 MODULE_LICENSE("GPL");
297