1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * The driver for Measurement Specialties HTU31 Temperature and Humidity sensor.
4 *
5 * Copyright (C) 2025
6 * Author: Andrei Lalaev <andrey.lalaev@gmail.com>
7 */
8
9#include <linux/array_size.h>
10#include <linux/cleanup.h>
11#include <linux/crc8.h>
12#include <linux/debugfs.h>
13#include <linux/delay.h>
14#include <linux/hwmon.h>
15#include <linux/hwmon-sysfs.h>
16#include <linux/i2c.h>
17#include <linux/init.h>
18#include <linux/module.h>
19
20#define HTU31_READ_TEMP_HUM_CMD 0x00
21#define HTU31_READ_SERIAL_CMD 0x0a
22#define HTU31_CONVERSION_CMD 0x5e
23#define HTU31_HEATER_OFF_CMD 0x02
24#define HTU31_HEATER_ON_CMD 0x04
25
26#define HTU31_TEMP_HUM_LEN 6
27
28/* Conversion time for the highest resolution */
29#define HTU31_HUMIDITY_CONV_TIME 10000 /* us */
30#define HTU31_TEMPERATURE_CONV_TIME 15000 /* us */
31
32#define HTU31_SERIAL_NUMBER_LEN 3
33#define HTU31_SERIAL_NUMBER_CRC_LEN 1
34#define HTU31_SERIAL_NUMBER_CRC_OFFSET 3
35
36#define HTU31_CRC8_INIT_VAL 0
37#define HTU31_CRC8_POLYNOMIAL 0x31
38DECLARE_CRC8_TABLE(htu31_crc8_table);
39
40/**
41 * struct htu31_data - all the data required to operate a HTU31 chip
42 * @client: the i2c client associated with the HTU31
43 * @lock: a mutex to prevent parallel access to the data
44 * @wait_time: the time needed by sensor to convert values
45 * @temperature: the latest temperature value in millidegrees
46 * @humidity: the latest relative humidity value in millipercent
47 * @serial_number: the serial number of the sensor
48 * @heater_enable: the internal state of the heater
49 */
50struct htu31_data {
51 struct i2c_client *client;
52 struct mutex lock; /* Used to protect against parallel data updates */
53 long wait_time;
54 long temperature;
55 long humidity;
56 u8 serial_number[HTU31_SERIAL_NUMBER_LEN];
57 bool heater_enable;
58};
59
60static long htu31_temp_to_millicelsius(u16 val)
61{
62 return -40000 + DIV_ROUND_CLOSEST_ULL(165000ULL * val, 65535);
63}
64
65static long htu31_relative_humidity(u16 val)
66{
67 return DIV_ROUND_CLOSEST_ULL(100000ULL * val, 65535);
68}
69
70static int htu31_data_fetch_command(struct htu31_data *data)
71{
72 struct i2c_client *client = data->client;
73 u8 conversion_on = HTU31_CONVERSION_CMD;
74 u8 read_data_cmd = HTU31_READ_TEMP_HUM_CMD;
75 u8 t_h_buf[HTU31_TEMP_HUM_LEN] = {};
76 struct i2c_msg msgs[] = {
77 {
78 .addr = client->addr,
79 .flags = 0,
80 .len = 1,
81 .buf = &read_data_cmd,
82 },
83 {
84 .addr = client->addr,
85 .flags = I2C_M_RD,
86 .len = sizeof(t_h_buf),
87 .buf = t_h_buf,
88 },
89 };
90 int ret;
91 u8 crc;
92
93 guard(mutex)(T: &data->lock);
94
95 ret = i2c_master_send(client, buf: &conversion_on, count: 1);
96 if (ret != 1) {
97 ret = ret < 0 ? ret : -EIO;
98 dev_err(&client->dev,
99 "Conversion command is failed. Error code: %d\n", ret);
100 return ret;
101 }
102
103 fsleep(usecs: data->wait_time);
104
105 ret = i2c_transfer(adap: client->adapter, msgs, ARRAY_SIZE(msgs));
106 if (ret != ARRAY_SIZE(msgs)) {
107 ret = ret < 0 ? ret : -EIO;
108 dev_err(&client->dev,
109 "T&H command is failed. Error code: %d\n", ret);
110 return ret;
111 }
112
113 crc = crc8(table: htu31_crc8_table, pdata: &t_h_buf[0], nbytes: 2, HTU31_CRC8_INIT_VAL);
114 if (crc != t_h_buf[2]) {
115 dev_err(&client->dev, "Temperature CRC mismatch\n");
116 return -EIO;
117 }
118
119 crc = crc8(table: htu31_crc8_table, pdata: &t_h_buf[3], nbytes: 2, HTU31_CRC8_INIT_VAL);
120 if (crc != t_h_buf[5]) {
121 dev_err(&client->dev, "Humidity CRC mismatch\n");
122 return -EIO;
123 }
124
125 data->temperature = htu31_temp_to_millicelsius(be16_to_cpup(p: (__be16 *)&t_h_buf[0]));
126 data->humidity = htu31_relative_humidity(be16_to_cpup(p: (__be16 *)&t_h_buf[3]));
127
128 return 0;
129}
130
131static umode_t htu31_is_visible(const void *data, enum hwmon_sensor_types type,
132 u32 attr, int channel)
133{
134 switch (type) {
135 case hwmon_temp:
136 case hwmon_humidity:
137 return 0444;
138 default:
139 return 0;
140 }
141}
142
143static int htu31_read(struct device *dev, enum hwmon_sensor_types type,
144 u32 attr, int channel, long *val)
145{
146 struct htu31_data *data = dev_get_drvdata(dev);
147 int ret;
148
149 ret = htu31_data_fetch_command(data);
150 if (ret < 0)
151 return ret;
152
153 switch (type) {
154 case hwmon_temp:
155 if (attr != hwmon_temp_input)
156 return -EINVAL;
157
158 *val = data->temperature;
159 break;
160 case hwmon_humidity:
161 if (attr != hwmon_humidity_input)
162 return -EINVAL;
163
164 *val = data->humidity;
165 break;
166 default:
167 return -EOPNOTSUPP;
168 }
169
170 return 0;
171}
172
173static int htu31_read_serial_number(struct htu31_data *data)
174{
175 struct i2c_client *client = data->client;
176 u8 read_sn_cmd = HTU31_READ_SERIAL_CMD;
177 u8 sn_buf[HTU31_SERIAL_NUMBER_LEN + HTU31_SERIAL_NUMBER_CRC_LEN];
178 struct i2c_msg msgs[] = {
179 {
180 .addr = client->addr,
181 .flags = 0,
182 .len = 1,
183 .buf = &read_sn_cmd,
184 },
185 {
186 .addr = client->addr,
187 .flags = I2C_M_RD,
188 .len = sizeof(sn_buf),
189 .buf = sn_buf,
190 },
191 };
192 int ret;
193 u8 crc;
194
195 ret = i2c_transfer(adap: client->adapter, msgs, ARRAY_SIZE(msgs));
196 if (ret < 0)
197 return ret;
198
199 crc = crc8(table: htu31_crc8_table, pdata: sn_buf, HTU31_SERIAL_NUMBER_LEN, HTU31_CRC8_INIT_VAL);
200 if (crc != sn_buf[HTU31_SERIAL_NUMBER_CRC_OFFSET]) {
201 dev_err(&client->dev, "Serial number CRC mismatch\n");
202 return -EIO;
203 }
204
205 memcpy(data->serial_number, sn_buf, HTU31_SERIAL_NUMBER_LEN);
206
207 return 0;
208}
209
210static ssize_t heater_enable_show(struct device *dev,
211 struct device_attribute *attr,
212 char *buf)
213{
214 struct htu31_data *data = dev_get_drvdata(dev);
215
216 return sysfs_emit(buf, fmt: "%d\n", data->heater_enable);
217}
218
219static ssize_t heater_enable_store(struct device *dev,
220 struct device_attribute *attr,
221 const char *buf,
222 size_t count)
223{
224 struct htu31_data *data = dev_get_drvdata(dev);
225 u8 heater_cmd;
226 bool status;
227 int ret;
228
229 ret = kstrtobool(s: buf, res: &status);
230 if (ret)
231 return ret;
232
233 heater_cmd = status ? HTU31_HEATER_ON_CMD : HTU31_HEATER_OFF_CMD;
234
235 guard(mutex)(T: &data->lock);
236
237 ret = i2c_master_send(client: data->client, buf: &heater_cmd, count: 1);
238 if (ret < 0)
239 return ret;
240
241 data->heater_enable = status;
242
243 return count;
244}
245
246static DEVICE_ATTR_RW(heater_enable);
247
248static int serial_number_show(struct seq_file *seq_file,
249 void *unused)
250{
251 struct htu31_data *data = seq_file->private;
252
253 seq_printf(m: seq_file, fmt: "%X%X%X\n", data->serial_number[0],
254 data->serial_number[1], data->serial_number[2]);
255 return 0;
256}
257
258DEFINE_SHOW_ATTRIBUTE(serial_number);
259
260static struct attribute *htu31_attrs[] = {
261 &dev_attr_heater_enable.attr,
262 NULL
263};
264
265ATTRIBUTE_GROUPS(htu31);
266
267static const struct hwmon_channel_info * const htu31_info[] = {
268 HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
269 HWMON_CHANNEL_INFO(humidity, HWMON_H_INPUT),
270 NULL
271};
272
273static const struct hwmon_ops htu31_hwmon_ops = {
274 .is_visible = htu31_is_visible,
275 .read = htu31_read,
276};
277
278static const struct hwmon_chip_info htu31_chip_info = {
279 .info = htu31_info,
280 .ops = &htu31_hwmon_ops,
281};
282
283static int htu31_probe(struct i2c_client *client)
284{
285 struct device *dev = &client->dev;
286 struct device *hwmon_dev;
287 struct htu31_data *data;
288 int ret;
289
290 data = devm_kzalloc(dev, size: sizeof(*data), GFP_KERNEL);
291 if (!data)
292 return -ENOMEM;
293
294 data->client = client;
295 data->wait_time = HTU31_TEMPERATURE_CONV_TIME + HTU31_HUMIDITY_CONV_TIME;
296
297 ret = devm_mutex_init(dev, &data->lock);
298 if (ret)
299 return ret;
300
301 crc8_populate_msb(table: htu31_crc8_table, HTU31_CRC8_POLYNOMIAL);
302
303 ret = htu31_read_serial_number(data);
304 if (ret) {
305 dev_err(dev, "Failed to read serial number\n");
306 return ret;
307 }
308
309 debugfs_create_file("serial_number",
310 0444,
311 client->debugfs,
312 data,
313 &serial_number_fops);
314
315 hwmon_dev = devm_hwmon_device_register_with_info(dev,
316 name: client->name,
317 drvdata: data,
318 info: &htu31_chip_info,
319 extra_groups: htu31_groups);
320
321 return PTR_ERR_OR_ZERO(ptr: hwmon_dev);
322}
323
324static const struct i2c_device_id htu31_id[] = {
325 { "htu31" },
326 { }
327};
328MODULE_DEVICE_TABLE(i2c, htu31_id);
329
330#if IS_ENABLED(CONFIG_OF)
331static const struct of_device_id htu31_of_match[] = {
332 { .compatible = "meas,htu31" },
333 { }
334};
335MODULE_DEVICE_TABLE(of, htu31_of_match);
336#endif
337
338static struct i2c_driver htu31_driver = {
339 .driver = {
340 .name = "htu31",
341 .of_match_table = of_match_ptr(htu31_of_match),
342 },
343 .probe = htu31_probe,
344 .id_table = htu31_id,
345};
346module_i2c_driver(htu31_driver);
347
348MODULE_AUTHOR("Andrei Lalaev <andrey.lalaev@gmail.com>");
349MODULE_DESCRIPTION("HTU31 Temperature and Humidity sensor driver");
350MODULE_LICENSE("GPL");
351

source code of linux/drivers/hwmon/htu31.c