linux/drivers/hwmon/htu21.c
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   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 device *hwmon_dev;
  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 i2c_client *client)
  63{
  64        int ret = 0;
  65        struct htu21 *htu21 = i2c_get_clientdata(client);
  66
  67        mutex_lock(&htu21->lock);
  68
  69        if (time_after(jiffies, htu21->last_update + HZ / 2) ||
  70            !htu21->valid) {
  71                ret = i2c_smbus_read_word_swapped(client,
  72                                                  HTU21_T_MEASUREMENT_HM);
  73                if (ret < 0)
  74                        goto out;
  75                htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
  76                ret = i2c_smbus_read_word_swapped(client,
  77                                                  HTU21_RH_MEASUREMENT_HM);
  78                if (ret < 0)
  79                        goto out;
  80                htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
  81                htu21->last_update = jiffies;
  82                htu21->valid = true;
  83        }
  84out:
  85        mutex_unlock(&htu21->lock);
  86
  87        return ret >= 0 ? 0 : ret;
  88}
  89
  90static ssize_t htu21_show_temperature(struct device *dev,
  91                                      struct device_attribute *attr, char *buf)
  92{
  93        struct i2c_client *client = to_i2c_client(dev);
  94        struct htu21 *htu21 = i2c_get_clientdata(client);
  95        int ret = htu21_update_measurements(client);
  96        if (ret < 0)
  97                return ret;
  98        return sprintf(buf, "%d\n", htu21->temperature);
  99}
 100
 101static ssize_t htu21_show_humidity(struct device *dev,
 102                                   struct device_attribute *attr, char *buf)
 103{
 104        struct i2c_client *client = to_i2c_client(dev);
 105        struct htu21 *htu21 = i2c_get_clientdata(client);
 106        int ret = htu21_update_measurements(client);
 107        if (ret < 0)
 108                return ret;
 109        return sprintf(buf, "%d\n", htu21->humidity);
 110}
 111
 112static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
 113                          htu21_show_temperature, NULL, 0);
 114static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
 115                          htu21_show_humidity, NULL, 0);
 116
 117static struct attribute *htu21_attributes[] = {
 118        &sensor_dev_attr_temp1_input.dev_attr.attr,
 119        &sensor_dev_attr_humidity1_input.dev_attr.attr,
 120        NULL
 121};
 122
 123static const struct attribute_group htu21_group = {
 124        .attrs = htu21_attributes,
 125};
 126
 127static int htu21_probe(struct i2c_client *client,
 128                       const struct i2c_device_id *id)
 129{
 130        struct htu21 *htu21;
 131        int err;
 132
 133        if (!i2c_check_functionality(client->adapter,
 134                                     I2C_FUNC_SMBUS_READ_WORD_DATA)) {
 135                dev_err(&client->dev,
 136                        "adapter does not support SMBus word transactions\n");
 137                return -ENODEV;
 138        }
 139
 140        htu21 = devm_kzalloc(&client->dev, sizeof(*htu21), GFP_KERNEL);
 141        if (!htu21)
 142                return -ENOMEM;
 143
 144        i2c_set_clientdata(client, htu21);
 145
 146        mutex_init(&htu21->lock);
 147
 148        err = sysfs_create_group(&client->dev.kobj, &htu21_group);
 149        if (err) {
 150                dev_dbg(&client->dev, "could not create sysfs files\n");
 151                return err;
 152        }
 153        htu21->hwmon_dev = hwmon_device_register(&client->dev);
 154        if (IS_ERR(htu21->hwmon_dev)) {
 155                dev_dbg(&client->dev, "unable to register hwmon device\n");
 156                err = PTR_ERR(htu21->hwmon_dev);
 157                goto error;
 158        }
 159
 160        dev_info(&client->dev, "initialized\n");
 161
 162        return 0;
 163
 164error:
 165        sysfs_remove_group(&client->dev.kobj, &htu21_group);
 166        return err;
 167}
 168
 169static int htu21_remove(struct i2c_client *client)
 170{
 171        struct htu21 *htu21 = i2c_get_clientdata(client);
 172
 173        hwmon_device_unregister(htu21->hwmon_dev);
 174        sysfs_remove_group(&client->dev.kobj, &htu21_group);
 175
 176        return 0;
 177}
 178
 179static const struct i2c_device_id htu21_id[] = {
 180        { "htu21", 0 },
 181        { }
 182};
 183MODULE_DEVICE_TABLE(i2c, htu21_id);
 184
 185static struct i2c_driver htu21_driver = {
 186        .class = I2C_CLASS_HWMON,
 187        .driver = {
 188                .name   = "htu21",
 189        },
 190        .probe       = htu21_probe,
 191        .remove      = htu21_remove,
 192        .id_table    = htu21_id,
 193};
 194
 195module_i2c_driver(htu21_driver);
 196
 197MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
 198MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
 199MODULE_LICENSE("GPL");
 200
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