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
33struct 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
42static 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
52static 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
62static 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	}
85out:
86	mutex_unlock(&htu21->lock);
87
88	return ret >= 0 ? 0 : ret;
89}
90
91static 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
103static 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
115static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
116			  htu21_show_temperature, NULL, 0);
117static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
118			  htu21_show_humidity, NULL, 0);
119
120static 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
126ATTRIBUTE_GROUPS(htu21);
127
128static 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
155static const struct i2c_device_id htu21_id[] = {
156	{ "htu21", 0 },
157	{ }
158};
159MODULE_DEVICE_TABLE(i2c, htu21_id);
160
161static 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
170module_i2c_driver(htu21_driver);
171
172MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
173MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
174MODULE_LICENSE("GPL");
175