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 at http://www.sensirion.com/file/datasheet_sht21
20 */
21
22#include <linux/module.h>
23#include <linux/init.h>
24#include <linux/slab.h>
25#include <linux/i2c.h>
26#include <linux/hwmon.h>
27#include <linux/hwmon-sysfs.h>
28#include <linux/err.h>
29#include <linux/mutex.h>
30#include <linux/device.h>
31#include <linux/jiffies.h>
32
33/* I2C command bytes */
34#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
35#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
36#define SHT21_READ_SNB_CMD1 0xFA
37#define SHT21_READ_SNB_CMD2 0x0F
38#define SHT21_READ_SNAC_CMD1 0xFC
39#define SHT21_READ_SNAC_CMD2 0xC9
40
41/**
42 * struct sht21 - SHT21 device specific data
43 * @client: I2C client device
44 * @lock: mutex to protect measurement values
45 * @last_update: time of last update (jiffies)
46 * @temperature: cached temperature measurement value
47 * @humidity: cached humidity measurement value
48 * @valid: only 0 before first measurement is taken
49 * @eic: cached electronic identification code text
50 */
51struct sht21 {
52 struct i2c_client *client;
53 struct mutex lock;
54 unsigned long last_update;
55 int temperature;
56 int humidity;
57 char valid;
58 char eic[18];
59};
60
61/**
62 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
63 * milli celsius
64 * @ticks: temperature ticks value received from sensor
65 */
66static inline int sht21_temp_ticks_to_millicelsius(int ticks)
67{
68 ticks &= ~0x0003; /* clear status bits */
69 /*
70 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
71 * optimized for integer fixed point (3 digits) arithmetic
72 */
73 return ((21965 * ticks) >> 13) - 46850;
74}
75
76/**
77 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
78 * one-thousandths of a percent relative humidity
79 * @ticks: humidity ticks value received from sensor
80 */
81static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
82{
83 ticks &= ~0x0003; /* clear status bits */
84 /*
85 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
86 * optimized for integer fixed point (3 digits) arithmetic
87 */
88 return ((15625 * ticks) >> 13) - 6000;
89}
90
91/**
92 * sht21_update_measurements() - get updated measurements from device
93 * @dev: device
94 *
95 * Returns 0 on success, else negative errno.
96 */
97static int sht21_update_measurements(struct device *dev)
98{
99 int ret = 0;
100 struct sht21 *sht21 = dev_get_drvdata(dev);
101 struct i2c_client *client = sht21->client;
102
103 mutex_lock(&sht21->lock);
104 /*
105 * Data sheet 2.4:
106 * SHT2x should not be active for more than 10% of the time - e.g.
107 * maximum two measurements per second at 12bit accuracy shall be made.
108 */
109 if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
110 ret = i2c_smbus_read_word_swapped(client,
111 SHT21_TRIG_T_MEASUREMENT_HM);
112 if (ret < 0)
113 goto out;
114 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
115 ret = i2c_smbus_read_word_swapped(client,
116 SHT21_TRIG_RH_MEASUREMENT_HM);
117 if (ret < 0)
118 goto out;
119 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
120 sht21->last_update = jiffies;
121 sht21->valid = 1;
122 }
123out:
124 mutex_unlock(&sht21->lock);
125
126 return ret >= 0 ? 0 : ret;
127}
128
129/**
130 * sht21_show_temperature() - show temperature measurement value in sysfs
131 * @dev: device
132 * @attr: device attribute
133 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
134 *
135 * Will be called on read access to temp1_input sysfs attribute.
136 * Returns number of bytes written into buffer, negative errno on error.
137 */
138static ssize_t sht21_temperature_show(struct device *dev,
139 struct device_attribute *attr,
140 char *buf)
141{
142 struct sht21 *sht21 = dev_get_drvdata(dev);
143 int ret;
144
145 ret = sht21_update_measurements(dev);
146 if (ret < 0)
147 return ret;
148 return sprintf(buf, "%d\n", sht21->temperature);
149}
150
151/**
152 * sht21_show_humidity() - show humidity measurement value in sysfs
153 * @dev: device
154 * @attr: device attribute
155 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
156 *
157 * Will be called on read access to humidity1_input sysfs attribute.
158 * Returns number of bytes written into buffer, negative errno on error.
159 */
160static ssize_t sht21_humidity_show(struct device *dev,
161 struct device_attribute *attr, char *buf)
162{
163 struct sht21 *sht21 = dev_get_drvdata(dev);
164 int ret;
165
166 ret = sht21_update_measurements(dev);
167 if (ret < 0)
168 return ret;
169 return sprintf(buf, "%d\n", sht21->humidity);
170}
171
172static ssize_t eic_read(struct sht21 *sht21)
173{
174 struct i2c_client *client = sht21->client;
175 u8 tx[2];
176 u8 rx[8];
177 u8 eic[8];
178 struct i2c_msg msgs[2] = {
179 {
180 .addr = client->addr,
181 .flags = 0,
182 .len = 2,
183 .buf = tx,
184 },
185 {
186 .addr = client->addr,
187 .flags = I2C_M_RD,
188 .len = 8,
189 .buf = rx,
190 },
191 };
192 int ret;
193
194 tx[0] = SHT21_READ_SNB_CMD1;
195 tx[1] = SHT21_READ_SNB_CMD2;
196 ret = i2c_transfer(client->adapter, msgs, 2);
197 if (ret < 0)
198 goto out;
199 eic[2] = rx[0];
200 eic[3] = rx[2];
201 eic[4] = rx[4];
202 eic[5] = rx[6];
203
204 tx[0] = SHT21_READ_SNAC_CMD1;
205 tx[1] = SHT21_READ_SNAC_CMD2;
206 msgs[1].len = 6;
207 ret = i2c_transfer(client->adapter, msgs, 2);
208 if (ret < 0)
209 goto out;
210 eic[0] = rx[3];
211 eic[1] = rx[4];
212 eic[6] = rx[0];
213 eic[7] = rx[1];
214
215 ret = snprintf(sht21->eic, sizeof(sht21->eic),
216 "%02x%02x%02x%02x%02x%02x%02x%02x\n",
217 eic[0], eic[1], eic[2], eic[3],
218 eic[4], eic[5], eic[6], eic[7]);
219out:
220 if (ret < 0)
221 sht21->eic[0] = 0;
222
223 return ret;
224}
225
226/**
227 * eic_show() - show Electronic Identification Code in sysfs
228 * @dev: device
229 * @attr: device attribute
230 * @buf: sysfs buffer (PAGE_SIZE) where EIC is written
231 *
232 * Will be called on read access to eic sysfs attribute.
233 * Returns number of bytes written into buffer, negative errno on error.
234 */
235static ssize_t eic_show(struct device *dev,
236 struct device_attribute *attr,
237 char *buf)
238{
239 struct sht21 *sht21 = dev_get_drvdata(dev);
240 int ret;
241
242 ret = sizeof(sht21->eic) - 1;
243 mutex_lock(&sht21->lock);
244 if (!sht21->eic[0])
245 ret = eic_read(sht21);
246 if (ret > 0)
247 memcpy(buf, sht21->eic, ret);
248 mutex_unlock(&sht21->lock);
249 return ret;
250}
251
252/* sysfs attributes */
253static SENSOR_DEVICE_ATTR_RO(temp1_input, sht21_temperature, 0);
254static SENSOR_DEVICE_ATTR_RO(humidity1_input, sht21_humidity, 0);
255static DEVICE_ATTR_RO(eic);
256
257static struct attribute *sht21_attrs[] = {
258 &sensor_dev_attr_temp1_input.dev_attr.attr,
259 &sensor_dev_attr_humidity1_input.dev_attr.attr,
260 &dev_attr_eic.attr,
261 NULL
262};
263
264ATTRIBUTE_GROUPS(sht21);
265
266static int sht21_probe(struct i2c_client *client,
267 const struct i2c_device_id *id)
268{
269 struct device *dev = &client->dev;
270 struct device *hwmon_dev;
271 struct sht21 *sht21;
272
273 if (!i2c_check_functionality(client->adapter,
274 I2C_FUNC_SMBUS_WORD_DATA)) {
275 dev_err(&client->dev,
276 "adapter does not support SMBus word transactions\n");
277 return -ENODEV;
278 }
279
280 sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
281 if (!sht21)
282 return -ENOMEM;
283
284 sht21->client = client;
285
286 mutex_init(&sht21->lock);
287
288 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
289 sht21, sht21_groups);
290 return PTR_ERR_OR_ZERO(hwmon_dev);
291}
292
293/* Device ID table */
294static const struct i2c_device_id sht21_id[] = {
295 { "sht21", 0 },
296 { }
297};
298MODULE_DEVICE_TABLE(i2c, sht21_id);
299
300static struct i2c_driver sht21_driver = {
301 .driver.name = "sht21",
302 .probe = sht21_probe,
303 .id_table = sht21_id,
304};
305
306module_i2c_driver(sht21_driver);
307
308MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
309MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
310MODULE_LICENSE("GPL");
311