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Urs Fleisch430400b2011-01-07 07:15:39 +00001/* 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>
Jean Delvaredcd8f392012-10-10 15:25:56 +020032#include <linux/jiffies.h>
Urs Fleisch430400b2011-01-07 07:15:39 +000033
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 device *hwmon_dev;
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/**
Urs Fleisch430400b2011-01-07 07:15:39 +000087 * sht21_update_measurements() - get updated measurements from device
88 * @client: I2C client device
89 *
90 * Returns 0 on success, else negative errno.
91 */
92static int sht21_update_measurements(struct i2c_client *client)
93{
94 int ret = 0;
95 struct sht21 *sht21 = i2c_get_clientdata(client);
96
97 mutex_lock(&sht21->lock);
98 /*
99 * Data sheet 2.4:
100 * SHT2x should not be active for more than 10% of the time - e.g.
101 * maximum two measurements per second at 12bit accuracy shall be made.
102 */
103 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
Jean Delvare90f41022011-11-04 12:00:47 +0100104 ret = i2c_smbus_read_word_swapped(client,
105 SHT21_TRIG_T_MEASUREMENT_HM);
Urs Fleisch430400b2011-01-07 07:15:39 +0000106 if (ret < 0)
107 goto out;
108 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
Jean Delvare90f41022011-11-04 12:00:47 +0100109 ret = i2c_smbus_read_word_swapped(client,
110 SHT21_TRIG_RH_MEASUREMENT_HM);
Urs Fleisch430400b2011-01-07 07:15:39 +0000111 if (ret < 0)
112 goto out;
113 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
114 sht21->last_update = jiffies;
115 sht21->valid = 1;
116 }
117out:
118 mutex_unlock(&sht21->lock);
119
120 return ret >= 0 ? 0 : ret;
121}
122
123/**
124 * sht21_show_temperature() - show temperature measurement value in sysfs
125 * @dev: device
126 * @attr: device attribute
127 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
128 *
129 * Will be called on read access to temp1_input sysfs attribute.
130 * Returns number of bytes written into buffer, negative errno on error.
131 */
132static ssize_t sht21_show_temperature(struct device *dev,
133 struct device_attribute *attr,
134 char *buf)
135{
136 struct i2c_client *client = to_i2c_client(dev);
137 struct sht21 *sht21 = i2c_get_clientdata(client);
138 int ret = sht21_update_measurements(client);
139 if (ret < 0)
140 return ret;
141 return sprintf(buf, "%d\n", sht21->temperature);
142}
143
144/**
145 * sht21_show_humidity() - show humidity measurement value in sysfs
146 * @dev: device
147 * @attr: device attribute
148 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
149 *
150 * Will be called on read access to humidity1_input sysfs attribute.
151 * Returns number of bytes written into buffer, negative errno on error.
152 */
153static ssize_t sht21_show_humidity(struct device *dev,
154 struct device_attribute *attr,
155 char *buf)
156{
157 struct i2c_client *client = to_i2c_client(dev);
158 struct sht21 *sht21 = i2c_get_clientdata(client);
159 int ret = sht21_update_measurements(client);
160 if (ret < 0)
161 return ret;
162 return sprintf(buf, "%d\n", sht21->humidity);
163}
164
165/* sysfs attributes */
166static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
167 NULL, 0);
168static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
169 NULL, 0);
170
171static struct attribute *sht21_attributes[] = {
172 &sensor_dev_attr_temp1_input.dev_attr.attr,
173 &sensor_dev_attr_humidity1_input.dev_attr.attr,
174 NULL
175};
176
177static const struct attribute_group sht21_attr_group = {
178 .attrs = sht21_attributes,
179};
180
181/**
182 * sht21_probe() - probe device
183 * @client: I2C client device
184 * @id: device ID
185 *
186 * Called by the I2C core when an entry in the ID table matches a
187 * device's name.
188 * Returns 0 on success.
189 */
Bill Pemberton6c931ae2012-11-19 13:22:35 -0500190static int sht21_probe(struct i2c_client *client,
Urs Fleisch430400b2011-01-07 07:15:39 +0000191 const struct i2c_device_id *id)
192{
193 struct sht21 *sht21;
194 int err;
195
196 if (!i2c_check_functionality(client->adapter,
197 I2C_FUNC_SMBUS_WORD_DATA)) {
198 dev_err(&client->dev,
199 "adapter does not support SMBus word transactions\n");
200 return -ENODEV;
201 }
202
Guenter Roecka844af192012-06-02 11:20:22 -0700203 sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL);
204 if (!sht21)
Urs Fleisch430400b2011-01-07 07:15:39 +0000205 return -ENOMEM;
Guenter Roecka844af192012-06-02 11:20:22 -0700206
Urs Fleisch430400b2011-01-07 07:15:39 +0000207 i2c_set_clientdata(client, sht21);
208
209 mutex_init(&sht21->lock);
210
211 err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
212 if (err) {
213 dev_dbg(&client->dev, "could not create sysfs files\n");
Guenter Roecka844af192012-06-02 11:20:22 -0700214 return err;
Urs Fleisch430400b2011-01-07 07:15:39 +0000215 }
216 sht21->hwmon_dev = hwmon_device_register(&client->dev);
217 if (IS_ERR(sht21->hwmon_dev)) {
218 dev_dbg(&client->dev, "unable to register hwmon device\n");
219 err = PTR_ERR(sht21->hwmon_dev);
220 goto fail_remove_sysfs;
221 }
222
223 dev_info(&client->dev, "initialized\n");
224
225 return 0;
226
227fail_remove_sysfs:
228 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
Urs Fleisch430400b2011-01-07 07:15:39 +0000229 return err;
230}
231
232/**
233 * sht21_remove() - remove device
234 * @client: I2C client device
235 */
Bill Pemberton281dfd02012-11-19 13:25:51 -0500236static int sht21_remove(struct i2c_client *client)
Urs Fleisch430400b2011-01-07 07:15:39 +0000237{
238 struct sht21 *sht21 = i2c_get_clientdata(client);
239
240 hwmon_device_unregister(sht21->hwmon_dev);
241 sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
Urs Fleisch430400b2011-01-07 07:15:39 +0000242
243 return 0;
244}
245
246/* Device ID table */
247static const struct i2c_device_id sht21_id[] = {
248 { "sht21", 0 },
249 { }
250};
251MODULE_DEVICE_TABLE(i2c, sht21_id);
252
253static struct i2c_driver sht21_driver = {
254 .driver.name = "sht21",
255 .probe = sht21_probe,
Bill Pemberton9e5e9b72012-11-19 13:21:20 -0500256 .remove = sht21_remove,
Urs Fleisch430400b2011-01-07 07:15:39 +0000257 .id_table = sht21_id,
258};
259
Axel Linf0967ee2012-01-20 15:38:18 +0800260module_i2c_driver(sht21_driver);
Urs Fleisch430400b2011-01-07 07:15:39 +0000261
262MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
263MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
264MODULE_LICENSE("GPL");