drivers/hwmon/sht21.c

   1 /* Sensirion SHT21 humidity and temperature sensor driver
   2  *
   3  * Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
  18  *
  19  * Data sheet available (5/2010) at
  20  * http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/init.h>
  25 #include <linux/slab.h>
  26 #include <linux/i2c.h>
  27 #include <linux/hwmon.h>
  28 #include <linux/hwmon-sysfs.h>
  29 #include <linux/err.h>
  30 #include <linux/mutex.h>
  31 #include <linux/device.h>
  32 #include <linux/jiffies.h>
  33
  34 /* I2C command bytes */
  35 #define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
  36 #define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
  37
  38 /**
  39  * struct sht21 - SHT21 device specific data
  40  * @hwmon_dev: device registered with hwmon
  41  * @lock: mutex to protect measurement values
  42  * @valid: only 0 before first measurement is taken
  43  * @last_update: time of last update (jiffies)
  44  * @temperature: cached temperature measurement value
  45  * @humidity: cached humidity measurement value
  46  */
  47 struct sht21 {
  48         struct i2c_client *client;
  49         struct mutex lock;
  50         char valid;
  51         unsigned long last_update;
  52         int temperature;
  53         int humidity;
  54 };
  55
  56 /**
  57  * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
  58  * milli celsius
  59  * @ticks: temperature ticks value received from sensor
  60  */
  61 static inline int sht21_temp_ticks_to_millicelsius(int ticks)
  62 {
  63         ticks &= ~0x0003; /* clear status bits */
  64         /*
  65          * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
  66          * optimized for integer fixed point (3 digits) arithmetic
  67          */
  68         return ((21965 * ticks) >> 13) - 46850;
  69 }
  70
  71 /**
  72  * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
  73  * one-thousandths of a percent relative humidity
  74  * @ticks: humidity ticks value received from sensor
  75  */
  76 static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
  77 {
  78         ticks &= ~0x0003; /* clear status bits */
  79         /*
  80          * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
  81          * optimized for integer fixed point (3 digits) arithmetic
  82          */
  83         return ((15625 * ticks) >> 13) - 6000;
  84 }
  85
  86 /**
  87  * sht21_update_measurements() - get updated measurements from device
  88  * @dev: device
  89  *
  90  * Returns 0 on success, else negative errno.
  91  */
  92 static int sht21_update_measurements(struct device *dev)
  93 {
  94         int ret = 0;
  95         struct sht21 *sht21 = dev_get_drvdata(dev);
  96         struct i2c_client *client = sht21->client;
  97
  98         mutex_lock(&sht21->lock);
  99         /*
 100          * Data sheet 2.4:
 101          * SHT2x should not be active for more than 10% of the time - e.g.
 102          * maximum two measurements per second at 12bit accuracy shall be made.
 103          */
 104         if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
 105                 ret = i2c_smbus_read_word_swapped(client,
 106                                                   SHT21_TRIG_T_MEASUREMENT_HM);
 107                 if (ret < 0)
 108                         goto out;
 109                 sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 110                 ret = i2c_smbus_read_word_swapped(client,
 111                                                   SHT21_TRIG_RH_MEASUREMENT_HM);
 112                 if (ret < 0)
 113                         goto out;
 114                 sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 115                 sht21->last_update = jiffies;
 116                 sht21->valid = 1;
 117         }
 118 out:
 119         mutex_unlock(&sht21->lock);
 120
 121         return ret >= 0 ? 0 : ret;
 122 }
 123
 124 /**
 125  * sht21_show_temperature() - show temperature measurement value in sysfs
 126  * @dev: device
 127  * @attr: device attribute
 128  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 129  *
 130  * Will be called on read access to temp1_input sysfs attribute.
 131  * Returns number of bytes written into buffer, negative errno on error.
 132  */
 133 static ssize_t sht21_show_temperature(struct device *dev,
 134         struct device_attribute *attr,
 135         char *buf)
 136 {
 137         struct sht21 *sht21 = dev_get_drvdata(dev);
 138         int ret;
 139
 140         ret = sht21_update_measurements(dev);
 141         if (ret < 0)
 142                 return ret;
 143         return sprintf(buf, "%d\n", sht21->temperature);
 144 }
 145
 146 /**
 147  * sht21_show_humidity() - show humidity measurement value in sysfs
 148  * @dev: device
 149  * @attr: device attribute
 150  * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 151  *
 152  * Will be called on read access to humidity1_input sysfs attribute.
 153  * Returns number of bytes written into buffer, negative errno on error.
 154  */
 155 static ssize_t sht21_show_humidity(struct device *dev,
 156         struct device_attribute *attr,
 157         char *buf)
 158 {
 159         struct sht21 *sht21 = dev_get_drvdata(dev);
 160         int ret;
 161
 162         ret = sht21_update_measurements(dev);
 163         if (ret < 0)
 164                 return ret;
 165         return sprintf(buf, "%d\n", sht21->humidity);
 166 }
 167
 168 /* sysfs attributes */
 169 static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
 170         NULL, 0);
 171 static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
 172         NULL, 0);
 173
 174 static struct attribute *sht21_attrs[] = {
 175         &sensor_dev_attr_temp1_input.dev_attr.attr,
 176         &sensor_dev_attr_humidity1_input.dev_attr.attr,
 177         NULL
 178 };
 179
 180 ATTRIBUTE_GROUPS(sht21);
 181
 182 static int sht21_probe(struct i2c_client *client,
 183         const struct i2c_device_id *id)
 184 {
 185         struct device *dev = &client->dev;
 186         struct device *hwmon_dev;
 187         struct sht21 *sht21;
 188
 189         if (!i2c_check_functionality(client->adapter,
 190                                      I2C_FUNC_SMBUS_WORD_DATA)) {
 191                 dev_err(&client->dev,
 192                         "adapter does not support SMBus word transactions\n");
 193                 return -ENODEV;
 194         }
 195
 196         sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
 197         if (!sht21)
 198                 return -ENOMEM;
 199
 200         sht21->client = client;
 201
 202         mutex_init(&sht21->lock);
 203
 204         hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
 205                                                            sht21, sht21_groups);
 206         return PTR_ERR_OR_ZERO(hwmon_dev);
 207 }
 208
 209 /* Device ID table */
 210 static const struct i2c_device_id sht21_id[] = {
 211         { "sht21", 0 },
 212         { }
 213 };
 214 MODULE_DEVICE_TABLE(i2c, sht21_id);
 215
 216 static struct i2c_driver sht21_driver = {
 217         .driver.name = "sht21",
 218         .probe       = sht21_probe,
 219         .id_table    = sht21_id,
 220 };
 221
 222 module_i2c_driver(sht21_driver);
 223
 224 MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 225 MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 226 MODULE_LICENSE("GPL");