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 */
47struct 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 */
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/**
87 * sht21_update_measurements() - get updated measurements from device
88 * @dev: device
89 *
90 * Returns 0 on success, else negative errno.
91 */
92static 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	}
118out:
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 */
133static 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 */
155static 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 */
169static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
170	NULL, 0);
171static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
172	NULL, 0);
173
174static 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
180ATTRIBUTE_GROUPS(sht21);
181
182static 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 */
210static const struct i2c_device_id sht21_id[] = {
211	{ "sht21", 0 },
212	{ }
213};
214MODULE_DEVICE_TABLE(i2c, sht21_id);
215
216static struct i2c_driver sht21_driver = {
217	.driver.name = "sht21",
218	.probe       = sht21_probe,
219	.id_table    = sht21_id,
220};
221
222module_i2c_driver(sht21_driver);
223
224MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
225MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
226MODULE_LICENSE("GPL");
227