1 /*
2 * Measurement Specialties HTU21D humidity and temperature sensor driver
3 *
4 * Copyright (C) 2013 William Markezana <william.markezana@meas-spec.com>
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 */
17
18 #include <linux/module.h>
19 #include <linux/init.h>
20 #include <linux/slab.h>
21 #include <linux/i2c.h>
22 #include <linux/hwmon.h>
23 #include <linux/hwmon-sysfs.h>
24 #include <linux/err.h>
25 #include <linux/mutex.h>
26 #include <linux/device.h>
27 #include <linux/jiffies.h>
28
29 /* HTU21 Commands */
30 #define HTU21_T_MEASUREMENT_HM 0xE3
31 #define HTU21_RH_MEASUREMENT_HM 0xE5
32
33 struct htu21 {
34 struct i2c_client *client;
35 struct mutex lock;
36 bool valid;
37 unsigned long last_update;
38 int temperature;
39 int humidity;
40 };
41
htu21_temp_ticks_to_millicelsius(int ticks)42 static inline int htu21_temp_ticks_to_millicelsius(int ticks)
43 {
44 ticks &= ~0x0003; /* clear status bits */
45 /*
46 * Formula T = -46.85 + 175.72 * ST / 2^16 from datasheet p14,
47 * optimized for integer fixed point (3 digits) arithmetic
48 */
49 return ((21965 * ticks) >> 13) - 46850;
50 }
51
htu21_rh_ticks_to_per_cent_mille(int ticks)52 static inline int htu21_rh_ticks_to_per_cent_mille(int ticks)
53 {
54 ticks &= ~0x0003; /* clear status bits */
55 /*
56 * Formula RH = -6 + 125 * SRH / 2^16 from datasheet p14,
57 * optimized for integer fixed point (3 digits) arithmetic
58 */
59 return ((15625 * ticks) >> 13) - 6000;
60 }
61
htu21_update_measurements(struct device * dev)62 static int htu21_update_measurements(struct device *dev)
63 {
64 struct htu21 *htu21 = dev_get_drvdata(dev);
65 struct i2c_client *client = htu21->client;
66 int ret = 0;
67
68 mutex_lock(&htu21->lock);
69
70 if (time_after(jiffies, htu21->last_update + HZ / 2) ||
71 !htu21->valid) {
72 ret = i2c_smbus_read_word_swapped(client,
73 HTU21_T_MEASUREMENT_HM);
74 if (ret < 0)
75 goto out;
76 htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
77 ret = i2c_smbus_read_word_swapped(client,
78 HTU21_RH_MEASUREMENT_HM);
79 if (ret < 0)
80 goto out;
81 htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
82 htu21->last_update = jiffies;
83 htu21->valid = true;
84 }
85 out:
86 mutex_unlock(&htu21->lock);
87
88 return ret >= 0 ? 0 : ret;
89 }
90
htu21_show_temperature(struct device * dev,struct device_attribute * attr,char * buf)91 static ssize_t htu21_show_temperature(struct device *dev,
92 struct device_attribute *attr, char *buf)
93 {
94 struct htu21 *htu21 = dev_get_drvdata(dev);
95 int ret;
96
97 ret = htu21_update_measurements(dev);
98 if (ret < 0)
99 return ret;
100 return sprintf(buf, "%d\n", htu21->temperature);
101 }
102
htu21_show_humidity(struct device * dev,struct device_attribute * attr,char * buf)103 static ssize_t htu21_show_humidity(struct device *dev,
104 struct device_attribute *attr, char *buf)
105 {
106 struct htu21 *htu21 = dev_get_drvdata(dev);
107 int ret;
108
109 ret = htu21_update_measurements(dev);
110 if (ret < 0)
111 return ret;
112 return sprintf(buf, "%d\n", htu21->humidity);
113 }
114
115 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
116 htu21_show_temperature, NULL, 0);
117 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
118 htu21_show_humidity, NULL, 0);
119
120 static struct attribute *htu21_attrs[] = {
121 &sensor_dev_attr_temp1_input.dev_attr.attr,
122 &sensor_dev_attr_humidity1_input.dev_attr.attr,
123 NULL
124 };
125
126 ATTRIBUTE_GROUPS(htu21);
127
htu21_probe(struct i2c_client * client,const struct i2c_device_id * id)128 static int htu21_probe(struct i2c_client *client,
129 const struct i2c_device_id *id)
130 {
131 struct device *dev = &client->dev;
132 struct htu21 *htu21;
133 struct device *hwmon_dev;
134
135 if (!i2c_check_functionality(client->adapter,
136 I2C_FUNC_SMBUS_READ_WORD_DATA)) {
137 dev_err(&client->dev,
138 "adapter does not support SMBus word transactions\n");
139 return -ENODEV;
140 }
141
142 htu21 = devm_kzalloc(dev, sizeof(*htu21), GFP_KERNEL);
143 if (!htu21)
144 return -ENOMEM;
145
146 htu21->client = client;
147 mutex_init(&htu21->lock);
148
149 hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
150 htu21,
151 htu21_groups);
152 return PTR_ERR_OR_ZERO(hwmon_dev);
153 }
154
155 static const struct i2c_device_id htu21_id[] = {
156 { "htu21", 0 },
157 { }
158 };
159 MODULE_DEVICE_TABLE(i2c, htu21_id);
160
161 static struct i2c_driver htu21_driver = {
162 .class = I2C_CLASS_HWMON,
163 .driver = {
164 .name = "htu21",
165 },
166 .probe = htu21_probe,
167 .id_table = htu21_id,
168 };
169
170 module_i2c_driver(htu21_driver);
171
172 MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
173 MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
174 MODULE_LICENSE("GPL");
175