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 */
47 struct 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 */
sht21_temp_ticks_to_millicelsius(int ticks)61 static 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 */
sht21_rh_ticks_to_per_cent_mille(int ticks)76 static 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 */
sht21_update_measurements(struct device * dev)92 static 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 }
118 out:
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 */
sht21_show_temperature(struct device * dev,struct device_attribute * attr,char * buf)133 static 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 */
sht21_show_humidity(struct device * dev,struct device_attribute * attr,char * buf)155 static 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 */
169 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
170 NULL, 0);
171 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
172 NULL, 0);
173
174 static 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
180 ATTRIBUTE_GROUPS(sht21);
181
sht21_probe(struct i2c_client * client,const struct i2c_device_id * id)182 static 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 */
210 static const struct i2c_device_id sht21_id[] = {
211 { "sht21", 0 },
212 { }
213 };
214 MODULE_DEVICE_TABLE(i2c, sht21_id);
215
216 static struct i2c_driver sht21_driver = {
217 .driver.name = "sht21",
218 .probe = sht21_probe,
219 .id_table = sht21_id,
220 };
221
222 module_i2c_driver(sht21_driver);
223
224 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
225 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
226 MODULE_LICENSE("GPL");
227