drivers/hwmon/htu21.c

   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 device *hwmon_dev;
  35         struct mutex lock;
  36         bool valid;
  37         unsigned long last_update;
  38         int temperature;
  39         int humidity;
  40 };
  41
  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
  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
  62 static 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         }
  84 out:
  85         mutex_unlock(&htu21->lock);
  86
  87         return ret >= 0 ? 0 : ret;
  88 }
  89
  90 static 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
 101 static 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
 112 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
 113                           htu21_show_temperature, NULL, 0);
 114 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
 115                           htu21_show_humidity, NULL, 0);
 116
 117 static 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
 123 static const struct attribute_group htu21_group = {
 124         .attrs = htu21_attributes,
 125 };
 126
 127 static 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
 164 error:
 165         sysfs_remove_group(&client->dev.kobj, &htu21_group);
 166         return err;
 167 }
 168
 169 static 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
 179 static const struct i2c_device_id htu21_id[] = {
 180         { "htu21", 0 },
 181         { }
 182 };
 183 MODULE_DEVICE_TABLE(i2c, htu21_id);
 184
 185 static 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
 195 module_i2c_driver(htu21_driver);
 196
 197 MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
 198 MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
 199 MODULE_LICENSE("GPL");