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430400b8 UF |
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> | |
dcd8f392 | 32 | #include <linux/jiffies.h> |
430400b8 UF |
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 { | |
b8d56898 | 48 | struct i2c_client *client; |
430400b8 UF |
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 | */ | |
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 | */ | |
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 | ||
430400b8 UF |
86 | /** |
87 | * sht21_update_measurements() - get updated measurements from device | |
b8d56898 | 88 | * @dev: device |
430400b8 UF |
89 | * |
90 | * Returns 0 on success, else negative errno. | |
91 | */ | |
b8d56898 | 92 | static int sht21_update_measurements(struct device *dev) |
430400b8 UF |
93 | { |
94 | int ret = 0; | |
b8d56898 AL |
95 | struct sht21 *sht21 = dev_get_drvdata(dev); |
96 | struct i2c_client *client = sht21->client; | |
430400b8 UF |
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) { | |
90f4102c JD |
105 | ret = i2c_smbus_read_word_swapped(client, |
106 | SHT21_TRIG_T_MEASUREMENT_HM); | |
430400b8 UF |
107 | if (ret < 0) |
108 | goto out; | |
109 | sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); | |
90f4102c JD |
110 | ret = i2c_smbus_read_word_swapped(client, |
111 | SHT21_TRIG_RH_MEASUREMENT_HM); | |
430400b8 UF |
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 | */ | |
133 | static ssize_t sht21_show_temperature(struct device *dev, | |
134 | struct device_attribute *attr, | |
135 | char *buf) | |
136 | { | |
b8d56898 AL |
137 | struct sht21 *sht21 = dev_get_drvdata(dev); |
138 | int ret; | |
139 | ||
140 | ret = sht21_update_measurements(dev); | |
430400b8 UF |
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 | */ | |
155 | static ssize_t sht21_show_humidity(struct device *dev, | |
156 | struct device_attribute *attr, | |
157 | char *buf) | |
158 | { | |
b8d56898 AL |
159 | struct sht21 *sht21 = dev_get_drvdata(dev); |
160 | int ret; | |
161 | ||
162 | ret = sht21_update_measurements(dev); | |
430400b8 UF |
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 | ||
b8d56898 | 174 | static struct attribute *sht21_attrs[] = { |
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175 | &sensor_dev_attr_temp1_input.dev_attr.attr, |
176 | &sensor_dev_attr_humidity1_input.dev_attr.attr, | |
177 | NULL | |
178 | }; | |
179 | ||
b8d56898 | 180 | ATTRIBUTE_GROUPS(sht21); |
430400b8 | 181 | |
6c931ae1 | 182 | static int sht21_probe(struct i2c_client *client, |
430400b8 UF |
183 | const struct i2c_device_id *id) |
184 | { | |
b8d56898 AL |
185 | struct device *dev = &client->dev; |
186 | struct device *hwmon_dev; | |
430400b8 | 187 | struct sht21 *sht21; |
430400b8 UF |
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 | ||
b8d56898 | 196 | sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL); |
a844af19 | 197 | if (!sht21) |
430400b8 | 198 | return -ENOMEM; |
a844af19 | 199 | |
b8d56898 | 200 | sht21->client = client; |
430400b8 UF |
201 | |
202 | mutex_init(&sht21->lock); | |
203 | ||
b8d56898 AL |
204 | hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name, |
205 | sht21, sht21_groups); | |
206 | return PTR_ERR_OR_ZERO(hwmon_dev); | |
430400b8 UF |
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, | |
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219 | .id_table = sht21_id, |
220 | }; | |
221 | ||
f0967eea | 222 | module_i2c_driver(sht21_driver); |
430400b8 UF |
223 | |
224 | MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); | |
225 | MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); | |
226 | MODULE_LICENSE("GPL"); |