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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 | #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 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 | */ |
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 | |
86 | /** |
87 | * sht21_update_measurements() - get updated measurements from device |
88 | * @client: I2C client device |
89 | * |
90 | * Returns 0 on success, else negative errno. |
91 | */ |
92 | static 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) { |
104 | ret = i2c_smbus_read_word_swapped(client, |
105 | SHT21_TRIG_T_MEASUREMENT_HM); |
106 | if (ret < 0) |
107 | goto out; |
108 | sht21->temperature = sht21_temp_ticks_to_millicelsius(ret); |
109 | ret = i2c_smbus_read_word_swapped(client, |
110 | SHT21_TRIG_RH_MEASUREMENT_HM); |
111 | 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 | } |
117 | out: |
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 | */ |
132 | static 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 | */ |
153 | static 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 */ |
166 | static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature, |
167 | NULL, 0); |
168 | static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity, |
169 | NULL, 0); |
170 | |
171 | static 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 | |
177 | static 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 | */ |
190 | static int sht21_probe(struct i2c_client *client, |
191 | 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 | |
203 | sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL); |
204 | if (!sht21) |
205 | return -ENOMEM; |
206 | |
207 | 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"); |
214 | return err; |
215 | } |
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 | |
227 | fail_remove_sysfs: |
228 | sysfs_remove_group(&client->dev.kobj, &sht21_attr_group); |
229 | return err; |
230 | } |
231 | |
232 | /** |
233 | * sht21_remove() - remove device |
234 | * @client: I2C client device |
235 | */ |
236 | static int sht21_remove(struct i2c_client *client) |
237 | { |
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); |
242 | |
243 | return 0; |
244 | } |
245 | |
246 | /* Device ID table */ |
247 | static const struct i2c_device_id sht21_id[] = { |
248 | { "sht21", 0 }, |
249 | { } |
250 | }; |
251 | MODULE_DEVICE_TABLE(i2c, sht21_id); |
252 | |
253 | static struct i2c_driver sht21_driver = { |
254 | .driver.name = "sht21", |
255 | .probe = sht21_probe, |
256 | .remove = sht21_remove, |
257 | .id_table = sht21_id, |
258 | }; |
259 | |
260 | module_i2c_driver(sht21_driver); |
261 | |
262 | MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>"); |
263 | MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver"); |
264 | MODULE_LICENSE("GPL"); |
265 |
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