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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 at http://www.sensirion.com/file/datasheet_sht21
20 */
21
22#include <linux/module.h>
23#include <linux/init.h>
24#include <linux/slab.h>
25#include <linux/i2c.h>
26#include <linux/hwmon.h>
27#include <linux/hwmon-sysfs.h>
28#include <linux/err.h>
29#include <linux/mutex.h>
30#include <linux/device.h>
31#include <linux/jiffies.h>
32
33/* I2C command bytes */
34#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
35#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
36#define SHT21_READ_SNB_CMD1 0xFA
37#define SHT21_READ_SNB_CMD2 0x0F
38#define SHT21_READ_SNAC_CMD1 0xFC
39#define SHT21_READ_SNAC_CMD2 0xC9
40
41/**
42 * struct sht21 - SHT21 device specific data
43 * @client: I2C client device
44 * @lock: mutex to protect measurement values
45 * @last_update: time of last update (jiffies)
46 * @temperature: cached temperature measurement value
47 * @humidity: cached humidity measurement value
48 * @valid: only 0 before first measurement is taken
49 * @eic: cached electronic identification code text
50 */
51struct sht21 {
52 struct i2c_client *client;
53 struct mutex lock;
54 unsigned long last_update;
55 int temperature;
56 int humidity;
57 char valid;
58 char eic[18];
59};
60
61/**
62 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
63 * milli celsius
64 * @ticks: temperature ticks value received from sensor
65 */
66static inline int sht21_temp_ticks_to_millicelsius(int ticks)
67{
68 ticks &= ~0x0003; /* clear status bits */
69 /*
70 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
71 * optimized for integer fixed point (3 digits) arithmetic
72 */
73 return ((21965 * ticks) >> 13) - 46850;
74}
75
76/**
77 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
78 * one-thousandths of a percent relative humidity
79 * @ticks: humidity ticks value received from sensor
80 */
81static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
82{
83 ticks &= ~0x0003; /* clear status bits */
84 /*
85 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
86 * optimized for integer fixed point (3 digits) arithmetic
87 */
88 return ((15625 * ticks) >> 13) - 6000;
89}
90
91/**
92 * sht21_update_measurements() - get updated measurements from device
93 * @dev: device
94 *
95 * Returns 0 on success, else negative errno.
96 */
97static int sht21_update_measurements(struct device *dev)
98{
99 int ret = 0;
100 struct sht21 *sht21 = dev_get_drvdata(dev);
101 struct i2c_client *client = sht21->client;
102
103 mutex_lock(&sht21->lock);
104 /*
105 * Data sheet 2.4:
106 * SHT2x should not be active for more than 10% of the time - e.g.
107 * maximum two measurements per second at 12bit accuracy shall be made.
108 */
109 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
110 ret = i2c_smbus_read_word_swapped(client,
111 SHT21_TRIG_T_MEASUREMENT_HM);
112 if (ret < 0)
113 goto out;
114 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
115 ret = i2c_smbus_read_word_swapped(client,
116 SHT21_TRIG_RH_MEASUREMENT_HM);
117 if (ret < 0)
118 goto out;
119 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
120 sht21->last_update = jiffies;
121 sht21->valid = 1;
122 }
123out:
124 mutex_unlock(&sht21->lock);
125
126 return ret >= 0 ? 0 : ret;
127}
128
129/**
130 * sht21_show_temperature() - show temperature measurement value in sysfs
131 * @dev: device
132 * @attr: device attribute
133 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
134 *
135 * Will be called on read access to temp1_input sysfs attribute.
136 * Returns number of bytes written into buffer, negative errno on error.
137 */
138static ssize_t sht21_show_temperature(struct device *dev,
139 struct device_attribute *attr,
140 char *buf)
141{
142 struct sht21 *sht21 = dev_get_drvdata(dev);
143 int ret;
144
145 ret = sht21_update_measurements(dev);
146 if (ret < 0)
147 return ret;
148 return sprintf(buf, "%d\n", sht21->temperature);
149}
150
151/**
152 * sht21_show_humidity() - show humidity measurement value in sysfs
153 * @dev: device
154 * @attr: device attribute
155 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
156 *
157 * Will be called on read access to humidity1_input sysfs attribute.
158 * Returns number of bytes written into buffer, negative errno on error.
159 */
160static ssize_t sht21_show_humidity(struct device *dev,
161 struct device_attribute *attr,
162 char *buf)
163{
164 struct sht21 *sht21 = dev_get_drvdata(dev);
165 int ret;
166
167 ret = sht21_update_measurements(dev);
168 if (ret < 0)
169 return ret;
170 return sprintf(buf, "%d\n", sht21->humidity);
171}
172
173static ssize_t eic_read(struct sht21 *sht21)
174{
175 struct i2c_client *client = sht21->client;
176 u8 tx[2];
177 u8 rx[8];
178 u8 eic[8];
179 struct i2c_msg msgs[2] = {
180 {
181 .addr = client->addr,
182 .flags = 0,
183 .len = 2,
184 .buf = tx,
185 },
186 {
187 .addr = client->addr,
188 .flags = I2C_M_RD,
189 .len = 8,
190 .buf = rx,
191 },
192 };
193 int ret;
194
195 tx[0] = SHT21_READ_SNB_CMD1;
196 tx[1] = SHT21_READ_SNB_CMD2;
197 ret = i2c_transfer(client->adapter, msgs, 2);
198 if (ret < 0)
199 goto out;
200 eic[2] = rx[0];
201 eic[3] = rx[2];
202 eic[4] = rx[4];
203 eic[5] = rx[6];
204
205 tx[0] = SHT21_READ_SNAC_CMD1;
206 tx[1] = SHT21_READ_SNAC_CMD2;
207 msgs[1].len = 6;
208 ret = i2c_transfer(client->adapter, msgs, 2);
209 if (ret < 0)
210 goto out;
211 eic[0] = rx[3];
212 eic[1] = rx[4];
213 eic[6] = rx[0];
214 eic[7] = rx[1];
215
216 ret = snprintf(sht21->eic, sizeof(sht21->eic),
217 "%02x%02x%02x%02x%02x%02x%02x%02x\n",
218 eic[0], eic[1], eic[2], eic[3],
219 eic[4], eic[5], eic[6], eic[7]);
220out:
221 if (ret < 0)
222 sht21->eic[0] = 0;
223
224 return ret;
225}
226
227/**
228 * eic_show() - show Electronic Identification Code in sysfs
229 * @dev: device
230 * @attr: device attribute
231 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
232 *
233 * Will be called on read access to eic sysfs attribute.
234 * Returns number of bytes written into buffer, negative errno on error.
235 */
236static ssize_t eic_show(struct device *dev,
237 struct device_attribute *attr,
238 char *buf)
239{
240 struct sht21 *sht21 = dev_get_drvdata(dev);
241 int ret;
242
243 ret = sizeof(sht21->eic) - 1;
244 mutex_lock(&sht21->lock);
245 if (!sht21->eic[0])
246 ret = eic_read(sht21);
247 if (ret > 0)
248 memcpy(buf, sht21->eic, ret);
249 mutex_unlock(&sht21->lock);
250 return ret;
251}
252
253/* sysfs attributes */
254static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
255 NULL, 0);
256static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
257 NULL, 0);
258static DEVICE_ATTR_RO(eic);
259
260static struct attribute *sht21_attrs[] = {
261 &sensor_dev_attr_temp1_input.dev_attr.attr,
262 &sensor_dev_attr_humidity1_input.dev_attr.attr,
263 &dev_attr_eic.attr,
264 NULL
265};
266
267ATTRIBUTE_GROUPS(sht21);
268
269static int sht21_probe(struct i2c_client *client,
270 const struct i2c_device_id *id)
271{
272 struct device *dev = &client->dev;
273 struct device *hwmon_dev;
274 struct sht21 *sht21;
275
276 if (!i2c_check_functionality(client->adapter,
277 I2C_FUNC_SMBUS_WORD_DATA)) {
278 dev_err(&client->dev,
279 "adapter does not support SMBus word transactions\n");
280 return -ENODEV;
281 }
282
283 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
284 if (!sht21)
285 return -ENOMEM;
286
287 sht21->client = client;
288
289 mutex_init(&sht21->lock);
290
291 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
292 sht21, sht21_groups);
293 return PTR_ERR_OR_ZERO(hwmon_dev);
294}
295
296/* Device ID table */
297static const struct i2c_device_id sht21_id[] = {
298 { "sht21", 0 },
299 { }
300};
301MODULE_DEVICE_TABLE(i2c, sht21_id);
302
303static struct i2c_driver sht21_driver = {
304 .driver.name = "sht21",
305 .probe = sht21_probe,
306 .id_table = sht21_id,
307};
308
309module_i2c_driver(sht21_driver);
310
311MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
312MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
313MODULE_LICENSE("GPL");