linux/drivers/hwmon/sht21.c
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   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 */
  47struct sht21 {
  48        struct device *hwmon_dev;
  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 */
  61static 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 */
  76static 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 * @client: I2C client device
  89 *
  90 * Returns 0 on success, else negative errno.
  91 */
  92static int sht21_update_measurements(struct i2c_client *client)
  93{
  94        int ret = 0;
  95        struct sht21 *sht21 = i2c_get_clientdata(client);
  96
  97        mutex_lock(&sht21->lock);
  98        /*
  99         * Data sheet 2.4:
 100         * SHT2x should not be active for more than 10% of the time - e.g.
 101         * maximum two measurements per second at 12bit accuracy shall be made.
 102         */
 103        if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
 104                ret = i2c_smbus_read_word_swapped(client,
 105                                                  SHT21_TRIG_T_MEASUREMENT_HM);
 106                if (ret < 0)
 107                        goto out;
 108                sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 109                ret = i2c_smbus_read_word_swapped(client,
 110                                                  SHT21_TRIG_RH_MEASUREMENT_HM);
 111                if (ret < 0)
 112                        goto out;
 113                sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 114                sht21->last_update = jiffies;
 115                sht21->valid = 1;
 116        }
 117out:
 118        mutex_unlock(&sht21->lock);
 119
 120        return ret >= 0 ? 0 : ret;
 121}
 122
 123/**
 124 * sht21_show_temperature() - show temperature measurement value in sysfs
 125 * @dev: device
 126 * @attr: device attribute
 127 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 128 *
 129 * Will be called on read access to temp1_input sysfs attribute.
 130 * Returns number of bytes written into buffer, negative errno on error.
 131 */
 132static ssize_t sht21_show_temperature(struct device *dev,
 133        struct device_attribute *attr,
 134        char *buf)
 135{
 136        struct i2c_client *client = to_i2c_client(dev);
 137        struct sht21 *sht21 = i2c_get_clientdata(client);
 138        int ret = sht21_update_measurements(client);
 139        if (ret < 0)
 140                return ret;
 141        return sprintf(buf, "%d\n", sht21->temperature);
 142}
 143
 144/**
 145 * sht21_show_humidity() - show humidity measurement value in sysfs
 146 * @dev: device
 147 * @attr: device attribute
 148 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 149 *
 150 * Will be called on read access to humidity1_input sysfs attribute.
 151 * Returns number of bytes written into buffer, negative errno on error.
 152 */
 153static ssize_t sht21_show_humidity(struct device *dev,
 154        struct device_attribute *attr,
 155        char *buf)
 156{
 157        struct i2c_client *client = to_i2c_client(dev);
 158        struct sht21 *sht21 = i2c_get_clientdata(client);
 159        int ret = sht21_update_measurements(client);
 160        if (ret < 0)
 161                return ret;
 162        return sprintf(buf, "%d\n", sht21->humidity);
 163}
 164
 165/* sysfs attributes */
 166static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
 167        NULL, 0);
 168static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
 169        NULL, 0);
 170
 171static struct attribute *sht21_attributes[] = {
 172        &sensor_dev_attr_temp1_input.dev_attr.attr,
 173        &sensor_dev_attr_humidity1_input.dev_attr.attr,
 174        NULL
 175};
 176
 177static const struct attribute_group sht21_attr_group = {
 178        .attrs = sht21_attributes,
 179};
 180
 181/**
 182 * sht21_probe() - probe device
 183 * @client: I2C client device
 184 * @id: device ID
 185 *
 186 * Called by the I2C core when an entry in the ID table matches a
 187 * device's name.
 188 * Returns 0 on success.
 189 */
 190static int __devinit sht21_probe(struct i2c_client *client,
 191        const struct i2c_device_id *id)
 192{
 193        struct sht21 *sht21;
 194        int err;
 195
 196        if (!i2c_check_functionality(client->adapter,
 197                                     I2C_FUNC_SMBUS_WORD_DATA)) {
 198                dev_err(&client->dev,
 199                        "adapter does not support SMBus word transactions\n");
 200                return -ENODEV;
 201        }
 202
 203        sht21 = devm_kzalloc(&client->dev, sizeof(*sht21), GFP_KERNEL);
 204        if (!sht21)
 205                return -ENOMEM;
 206
 207        i2c_set_clientdata(client, sht21);
 208
 209        mutex_init(&sht21->lock);
 210
 211        err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
 212        if (err) {
 213                dev_dbg(&client->dev, "could not create sysfs files\n");
 214                return err;
 215        }
 216        sht21->hwmon_dev = hwmon_device_register(&client->dev);
 217        if (IS_ERR(sht21->hwmon_dev)) {
 218                dev_dbg(&client->dev, "unable to register hwmon device\n");
 219                err = PTR_ERR(sht21->hwmon_dev);
 220                goto fail_remove_sysfs;
 221        }
 222
 223        dev_info(&client->dev, "initialized\n");
 224
 225        return 0;
 226
 227fail_remove_sysfs:
 228        sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 229        return err;
 230}
 231
 232/**
 233 * sht21_remove() - remove device
 234 * @client: I2C client device
 235 */
 236static int __devexit sht21_remove(struct i2c_client *client)
 237{
 238        struct sht21 *sht21 = i2c_get_clientdata(client);
 239
 240        hwmon_device_unregister(sht21->hwmon_dev);
 241        sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 242
 243        return 0;
 244}
 245
 246/* Device ID table */
 247static const struct i2c_device_id sht21_id[] = {
 248        { "sht21", 0 },
 249        { }
 250};
 251MODULE_DEVICE_TABLE(i2c, sht21_id);
 252
 253static struct i2c_driver sht21_driver = {
 254        .driver.name = "sht21",
 255        .probe       = sht21_probe,
 256        .remove      = __devexit_p(sht21_remove),
 257        .id_table    = sht21_id,
 258};
 259
 260module_i2c_driver(sht21_driver);
 261
 262MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 263MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 264MODULE_LICENSE("GPL");
 265
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