aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/hwmon/sht21.c
blob: 5f67546950b1ebce2c4e59a92acded014445195a (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
/* Sensirion SHT21 humidity and temperature sensor driver
 *
 * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Data sheet available (5/2010) at
 * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/device.h>
#include <linux/jiffies.h>

/* I2C command bytes */
#define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5

/**
 * struct sht21 - SHT21 device specific data
 * @hwmon_dev: device registered with hwmon
 * @lock: mutex to protect measurement values
 * @valid: only 0 before first measurement is taken
 * @last_update: time of last update (jiffies)
 * @temperature: cached temperature measurement value
 * @humidity: cached humidity measurement value
 */
struct sht21 {
	struct device *hwmon_dev;
	struct mutex lock;
	char valid;
	unsigned long last_update;
	int temperature;
	int humidity;
};

/**
 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
 * milli celsius
 * @ticks: temperature ticks value received from sensor
 */
static inline int sht21_temp_ticks_to_millicelsius(int ticks)
{
	ticks &= ~0x0003; /* clear status bits */
	/*
	 * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
	 * optimized for integer fixed point (3 digits) arithmetic
	 */
	return ((21965 * ticks) >> 13) - 46850;
}

/**
 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
 * one-thousandths of a percent relative humidity
 * @ticks: humidity ticks value received from sensor
 */
static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
{
	ticks &= ~0x0003; /* clear status bits */
	/*
	 * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
	 * optimized for integer fixed point (3 digits) arithmetic
	 */
	return ((15625 * ticks) >> 13) - 6000;
}

/**
 * sht21_update_measurements() - get updated measurements from device
 * @client: I2C client device
 *
 * Returns 0 on success, else negative errno.
 */
static int sht21_update_measurements(struct i2c_client *client)
{
	int ret = 0;
	struct sht21 *sht21 = i2c_get_clientdata(client);

	mutex_lock(&sht21->lock);
	/*
	 * Data sheet 2.4:
	 * SHT2x should not be active for more than 10% of the time - e.g.
	 * maximum two measurements per second at 12bit accuracy shall be made.
	 */
	if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
		ret = i2c_smbus_read_word_swapped(client,
						  SHT21_TRIG_T_MEASUREMENT_HM);
		if (ret < 0)
			goto out;
		sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
		ret = i2c_smbus_read_word_swapped(client,
						  SHT21_TRIG_RH_MEASUREMENT_HM);
		if (ret < 0)
			goto out;
		sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
		sht21->last_update = jiffies;
		sht21->valid = 1;
	}
out:
	mutex_unlock(&sht21->lock);

	return ret >= 0 ? 0 : ret;
}

/**
 * sht21_show_temperature() - show temperature measurement value in sysfs
 * @dev: device
 * @attr: device attribute
 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 *
 * Will be called on read access to temp1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht21_show_temperature(struct device *dev,
	struct device_attribute *attr,
	char *buf)
{
	struct i2c_client *client = to_i2c_client(dev);
	struct sht21 *sht21 = i2c_get_clientdata(client);
	int ret = sht21_update_measurements(client);
	if (ret < 0)
		return ret;
	return sprintf(buf, "%d\n", sht21->temperature);
}

/**
 * sht21_show_humidity() - show humidity measurement value in sysfs
 * @dev: device
 * @attr: device attribute
 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 *
 * Will be called on read access to humidity1_input sysfs attribute.
 * Returns number of bytes written into buffer, negative errno on error.
 */
static ssize_t sht21_show_humidity(struct device *dev,
	struct device_attribute *attr,
	char *buf)
{
	struct i2c_client *client = to_i2c_client(dev);
	struct sht21 *sht21 = i2c_get_clientdata(client);
	int ret = sht21_update_measurements(client);
	if (ret < 0)
		return ret;
	return sprintf(buf, "%d\n", sht21->humidity);
}

/* sysfs attributes */
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
	NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
	NULL, 0);

static struct attribute *sht21_attributes[] = {
	&sensor_dev_attr_temp1_input.dev_attr.attr,
	&sensor_dev_attr_humidity1_input.dev_attr.attr,
	NULL
};

static const struct attribute_group sht21_attr_group = {
	.attrs = sht21_attributes,
};

/**
 * sht21_probe() - probe device
 * @client: I2C client device
 * @id: device ID
 *
 * Called by the I2C core when an entry in the ID table matches a
 * device's name.
 * Returns 0 on success.
 */
static int __devinit sht21_probe(struct i2c_client *client,
	const struct i2c_device_id *id)
{
	struct sht21 *sht21;
	int err;

	if (!i2c_check_functionality(client->adapter,
				     I2C_FUNC_SMBUS_WORD_DATA)) {
		dev_err(&client->dev,
			"adapter does not support SMBus word transactions\n");
		return -ENODEV;
	}

	sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL);
	if (!sht21)
		return -ENOMEM;

	i2c_set_clientdata(client, sht21);

	mutex_init(&sht21->lock);

	err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
	if (err) {
		dev_dbg(&client->dev, "could not create sysfs files\n");
		return err;
	}
	sht21->hwmon_dev = hwmon_device_register(&client->dev);
	if (IS_ERR(sht21->hwmon_dev)) {
		dev_dbg(&client->dev, "unable to register hwmon device\n");
		err = PTR_ERR(sht21->hwmon_dev);
		goto fail_remove_sysfs;
	}

	dev_info(&client->dev, "initialized\n");

	return 0;

fail_remove_sysfs:
	sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
	return err;
}

/**
 * sht21_remove() - remove device
 * @client: I2C client device
 */
static int __devexit sht21_remove(struct i2c_client *client)
{
	struct sht21 *sht21 = i2c_get_clientdata(client);

	hwmon_device_unregister(sht21->hwmon_dev);
	sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);

	return 0;
}

/* Device ID table */
static const struct i2c_device_id sht21_id[] = {
	{ "sht21", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, sht21_id);

static struct i2c_driver sht21_driver = {
	.driver.name = "sht21",
	.probe       = sht21_probe,
	.remove      = __devexit_p(sht21_remove),
	.id_table    = sht21_id,
};

module_i2c_driver(sht21_driver);

MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");