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 i2c_client *client;
  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 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
  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
 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
 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");