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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 | */ | |
46 | struct 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 | */ | |
60 | static 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 | */ | |
75 | static 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 | */ | |
92 | static 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 | */ | |
110 | static 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 | } | |
134 | out: | |
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 | */ | |
149 | static 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 | */ | |
170 | static 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 */ | |
183 | static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, | |
184 | NULL, 0); | |
185 | static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, | |
186 | NULL, 0); | |
187 | ||
188 | static 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 | ||
194 | static 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 | */ | |
207 | static 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 | ||
245 | fail_remove_sysfs: | |
246 | sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); | |
247 | fail_free: | |
248 | kfree(sht21); | |
249 | ||
250 | return err; | |
251 | } | |
252 | ||
253 | /** | |
254 | * sht21_remove() - remove device | |
255 | * @client: I2C client device | |
256 | */ | |
257 | static 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 */ | |
269 | static const struct i2c_device_id sht21_id[] = { | |
270 | { "sht21", 0 }, | |
271 | { } | |
272 | }; | |
273 | MODULE_DEVICE_TABLE(i2c, sht21_id); | |
274 | ||
275 | static 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 | */ | |
288 | static int __init sht21_init(void) | |
289 | { | |
290 | return i2c_add_driver(&sht21_driver); | |
291 | } | |
292 | module_init(sht21_init); | |
293 | ||
294 | /** | |
295 | * sht21_init() - clean up driver | |
296 | * | |
297 | * Called when module is removed. | |
298 | */ | |
299 | static void __exit sht21_exit(void) | |
300 | { | |
301 | i2c_del_driver(&sht21_driver); | |
302 | } | |
303 | module_exit(sht21_exit); | |
304 | ||
305 | MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); | |
306 | MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); | |
307 | MODULE_LICENSE("GPL"); |