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 | */ |
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 | */ |
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 | */ |
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(ticks: 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(ticks: ret); |
107 | sht21->last_update = jiffies; |
108 | sht21->valid = true; |
109 | } |
110 | out: |
111 | mutex_unlock(lock: &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 | */ |
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, fmt: "%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 | */ |
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, fmt: "%d\n" , sht21->humidity); |
157 | } |
158 | |
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(adap: client->adapter, msgs, num: 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(adap: client->adapter, msgs, num: 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(buf: sht21->eic, size: sizeof(sht21->eic), |
203 | fmt: "%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 | */ |
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(lock: &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 | |
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(adap: 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, size: 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, name: client->name, |
275 | drvdata: sht21, groups: sht21_groups); |
276 | return PTR_ERR_OR_ZERO(ptr: 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 | |