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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
33/* I2C command bytes */
34#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
35#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
36
37/**
38 * struct sht21 - SHT21 device specific data
39 * @hwmon_dev: device registered with hwmon
40 * @lock: mutex to protect measurement values
41 * @valid: only 0 before first measurement is taken
42 * @last_update: time of last update (jiffies)
43 * @temperature: cached temperature measurement value
44 * @humidity: cached humidity measurement value
45 */
46struct sht21 {
47 struct device *hwmon_dev;
48 struct mutex lock;
49 char valid;
50 unsigned long last_update;
51 int temperature;
52 int humidity;
53};
54
55/**
56 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
57 * milli celsius
58 * @ticks: temperature ticks value received from sensor
59 */
60static inline int sht21_temp_ticks_to_millicelsius(int ticks)
61{
62 ticks &= ~0x0003; /* clear status bits */
63 /*
64 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
65 * optimized for integer fixed point (3 digits) arithmetic
66 */
67 return ((21965 * ticks) >> 13) - 46850;
68}
69
70/**
71 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
72 * one-thousandths of a percent relative humidity
73 * @ticks: humidity ticks value received from sensor
74 */
75static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
76{
77 ticks &= ~0x0003; /* clear status bits */
78 /*
79 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
80 * optimized for integer fixed point (3 digits) arithmetic
81 */
82 return ((15625 * ticks) >> 13) - 6000;
83}
84
85/**
86 * sht21_read_word_data() - read word from register
87 * @client: I2C client device
88 * @reg: I2C command byte
89 *
90 * Returns value, negative errno on error.
91 */
92static inline int sht21_read_word_data(struct i2c_client *client, u8 reg)
93{
94 int ret = i2c_smbus_read_word_data(client, reg);
95 if (ret < 0)
96 return ret;
97 /*
98 * SMBus specifies low byte first, but the SHT21 returns MSB
99 * first, so we have to swab16 the values
100 */
101 return swab16(ret);
102}
103
104/**
105 * sht21_update_measurements() - get updated measurements from device
106 * @client: I2C client device
107 *
108 * Returns 0 on success, else negative errno.
109 */
110static int sht21_update_measurements(struct i2c_client *client)
111{
112 int ret = 0;
113 struct sht21 *sht21 = i2c_get_clientdata(client);
114
115 mutex_lock(&sht21->lock);
116 /*
117 * Data sheet 2.4:
118 * SHT2x should not be active for more than 10% of the time - e.g.
119 * maximum two measurements per second at 12bit accuracy shall be made.
120 */
121 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
122 ret = sht21_read_word_data(client, SHT21_TRIG_T_MEASUREMENT_HM);
123 if (ret < 0)
124 goto out;
125 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
126 ret = sht21_read_word_data(client,
127 SHT21_TRIG_RH_MEASUREMENT_HM);
128 if (ret < 0)
129 goto out;
130 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
131 sht21->last_update = jiffies;
132 sht21->valid = 1;
133 }
134out:
135 mutex_unlock(&sht21->lock);
136
137 return ret >= 0 ? 0 : ret;
138}
139
140/**
141 * sht21_show_temperature() - show temperature measurement value in sysfs
142 * @dev: device
143 * @attr: device attribute
144 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
145 *
146 * Will be called on read access to temp1_input sysfs attribute.
147 * Returns number of bytes written into buffer, negative errno on error.
148 */
149static ssize_t sht21_show_temperature(struct device *dev,
150 struct device_attribute *attr,
151 char *buf)
152{
153 struct i2c_client *client = to_i2c_client(dev);
154 struct sht21 *sht21 = i2c_get_clientdata(client);
155 int ret = sht21_update_measurements(client);
156 if (ret < 0)
157 return ret;
158 return sprintf(buf, "%d\n", sht21->temperature);
159}
160
161/**
162 * sht21_show_humidity() - show humidity measurement value in sysfs
163 * @dev: device
164 * @attr: device attribute
165 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
166 *
167 * Will be called on read access to humidity1_input sysfs attribute.
168 * Returns number of bytes written into buffer, negative errno on error.
169 */
170static ssize_t sht21_show_humidity(struct device *dev,
171 struct device_attribute *attr,
172 char *buf)
173{
174 struct i2c_client *client = to_i2c_client(dev);
175 struct sht21 *sht21 = i2c_get_clientdata(client);
176 int ret = sht21_update_measurements(client);
177 if (ret < 0)
178 return ret;
179 return sprintf(buf, "%d\n", sht21->humidity);
180}
181
182/* sysfs attributes */
183static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
184 NULL, 0);
185static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
186 NULL, 0);
187
188static struct attribute *sht21_attributes[] = {
189 &sensor_dev_attr_temp1_input.dev_attr.attr,
190 &sensor_dev_attr_humidity1_input.dev_attr.attr,
191 NULL
192};
193
194static const struct attribute_group sht21_attr_group = {
195 .attrs = sht21_attributes,
196};
197
198/**
199 * sht21_probe() - probe device
200 * @client: I2C client device
201 * @id: device ID
202 *
203 * Called by the I2C core when an entry in the ID table matches a
204 * device's name.
205 * Returns 0 on success.
206 */
207static int __devinit sht21_probe(struct i2c_client *client,
208 const struct i2c_device_id *id)
209{
210 struct sht21 *sht21;
211 int err;
212
213 if (!i2c_check_functionality(client->adapter,
214 I2C_FUNC_SMBUS_WORD_DATA)) {
215 dev_err(&client->dev,
216 "adapter does not support SMBus word transactions\n");
217 return -ENODEV;
218 }
219
220 sht21 = kzalloc(sizeof(*sht21), GFP_KERNEL);
221 if (!sht21) {
222 dev_dbg(&client->dev, "kzalloc failed\n");
223 return -ENOMEM;
224 }
225 i2c_set_clientdata(client, sht21);
226
227 mutex_init(&sht21->lock);
228
229 err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
230 if (err) {
231 dev_dbg(&client->dev, "could not create sysfs files\n");
232 goto fail_free;
233 }
234 sht21->hwmon_dev = hwmon_device_register(&client->dev);
235 if (IS_ERR(sht21->hwmon_dev)) {
236 dev_dbg(&client->dev, "unable to register hwmon device\n");
237 err = PTR_ERR(sht21->hwmon_dev);
238 goto fail_remove_sysfs;
239 }
240
241 dev_info(&client->dev, "initialized\n");
242
243 return 0;
244
245fail_remove_sysfs:
246 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
247fail_free:
248 kfree(sht21);
249
250 return err;
251}
252
253/**
254 * sht21_remove() - remove device
255 * @client: I2C client device
256 */
257static int __devexit sht21_remove(struct i2c_client *client)
258{
259 struct sht21 *sht21 = i2c_get_clientdata(client);
260
261 hwmon_device_unregister(sht21->hwmon_dev);
262 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
263 kfree(sht21);
264
265 return 0;
266}
267
268/* Device ID table */
269static const struct i2c_device_id sht21_id[] = {
270 { "sht21", 0 },
271 { }
272};
273MODULE_DEVICE_TABLE(i2c, sht21_id);
274
275static struct i2c_driver sht21_driver = {
276 .driver.name = "sht21",
277 .probe = sht21_probe,
278 .remove = __devexit_p(sht21_remove),
279 .id_table = sht21_id,
280};
281
282/**
283 * sht21_init() - initialize driver
284 *
285 * Called when kernel is booted or module is inserted.
286 * Returns 0 on success.
287 */
288static int __init sht21_init(void)
289{
290 return i2c_add_driver(&sht21_driver);
291}
292module_init(sht21_init);
293
294/**
295 * sht21_init() - clean up driver
296 *
297 * Called when module is removed.
298 */
299static void __exit sht21_exit(void)
300{
301 i2c_del_driver(&sht21_driver);
302}
303module_exit(sht21_exit);
304
305MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
306MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
307MODULE_LICENSE("GPL");
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");