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
  33/* I2C command bytes */
  34#define SHT21_TRIG_T_MEASUREMENT_HM  0xe3
  35#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
  36
  37/**
  38 * struct sht21 - SHT21 device specific data
  39 * @hwmon_dev: device registered with hwmon
  40 * @lock: mutex to protect measurement values
  41 * @valid: only 0 before first measurement is taken
  42 * @last_update: time of last update (jiffies)
  43 * @temperature: cached temperature measurement value
  44 * @humidity: cached humidity measurement value
  45 */
  46struct sht21 {
  47        struct device *hwmon_dev;
  48        struct mutex lock;
  49        char valid;
  50        unsigned long last_update;
  51        int temperature;
  52        int humidity;
  53};
  54
  55/**
  56 * sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
  57 * milli celsius
  58 * @ticks: temperature ticks value received from sensor
  59 */
  60static inline int sht21_temp_ticks_to_millicelsius(int ticks)
  61{
  62        ticks &= ~0x0003; /* clear status bits */
  63        /*
  64         * Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
  65         * optimized for integer fixed point (3 digits) arithmetic
  66         */
  67        return ((21965 * ticks) >> 13) - 46850;
  68}
  69
  70/**
  71 * sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
  72 * one-thousandths of a percent relative humidity
  73 * @ticks: humidity ticks value received from sensor
  74 */
  75static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
  76{
  77        ticks &= ~0x0003; /* clear status bits */
  78        /*
  79         * Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
  80         * optimized for integer fixed point (3 digits) arithmetic
  81         */
  82        return ((15625 * ticks) >> 13) - 6000;
  83}
  84
  85/**
  86 * sht21_update_measurements() - get updated measurements from device
  87 * @client: I2C client device
  88 *
  89 * Returns 0 on success, else negative errno.
  90 */
  91static int sht21_update_measurements(struct i2c_client *client)
  92{
  93        int ret = 0;
  94        struct sht21 *sht21 = i2c_get_clientdata(client);
  95
  96        mutex_lock(&sht21->lock);
  97        /*
  98         * Data sheet 2.4:
  99         * SHT2x should not be active for more than 10% of the time - e.g.
 100         * maximum two measurements per second at 12bit accuracy shall be made.
 101         */
 102        if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
 103                ret = i2c_smbus_read_word_swapped(client,
 104                                                  SHT21_TRIG_T_MEASUREMENT_HM);
 105                if (ret < 0)
 106                        goto out;
 107                sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
 108                ret = i2c_smbus_read_word_swapped(client,
 109                                                  SHT21_TRIG_RH_MEASUREMENT_HM);
 110                if (ret < 0)
 111                        goto out;
 112                sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
 113                sht21->last_update = jiffies;
 114                sht21->valid = 1;
 115        }
 116out:
 117        mutex_unlock(&sht21->lock);
 118
 119        return ret >= 0 ? 0 : ret;
 120}
 121
 122/**
 123 * sht21_show_temperature() - show temperature measurement value in sysfs
 124 * @dev: device
 125 * @attr: device attribute
 126 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 127 *
 128 * Will be called on read access to temp1_input sysfs attribute.
 129 * Returns number of bytes written into buffer, negative errno on error.
 130 */
 131static ssize_t sht21_show_temperature(struct device *dev,
 132        struct device_attribute *attr,
 133        char *buf)
 134{
 135        struct i2c_client *client = to_i2c_client(dev);
 136        struct sht21 *sht21 = i2c_get_clientdata(client);
 137        int ret = sht21_update_measurements(client);
 138        if (ret < 0)
 139                return ret;
 140        return sprintf(buf, "%d\n", sht21->temperature);
 141}
 142
 143/**
 144 * sht21_show_humidity() - show humidity measurement value in sysfs
 145 * @dev: device
 146 * @attr: device attribute
 147 * @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
 148 *
 149 * Will be called on read access to humidity1_input sysfs attribute.
 150 * Returns number of bytes written into buffer, negative errno on error.
 151 */
 152static ssize_t sht21_show_humidity(struct device *dev,
 153        struct device_attribute *attr,
 154        char *buf)
 155{
 156        struct i2c_client *client = to_i2c_client(dev);
 157        struct sht21 *sht21 = i2c_get_clientdata(client);
 158        int ret = sht21_update_measurements(client);
 159        if (ret < 0)
 160                return ret;
 161        return sprintf(buf, "%d\n", sht21->humidity);
 162}
 163
 164/* sysfs attributes */
 165static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
 166        NULL, 0);
 167static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
 168        NULL, 0);
 169
 170static struct attribute *sht21_attributes[] = {
 171        &sensor_dev_attr_temp1_input.dev_attr.attr,
 172        &sensor_dev_attr_humidity1_input.dev_attr.attr,
 173        NULL
 174};
 175
 176static const struct attribute_group sht21_attr_group = {
 177        .attrs = sht21_attributes,
 178};
 179
 180/**
 181 * sht21_probe() - probe device
 182 * @client: I2C client device
 183 * @id: device ID
 184 *
 185 * Called by the I2C core when an entry in the ID table matches a
 186 * device's name.
 187 * Returns 0 on success.
 188 */
 189static int __devinit sht21_probe(struct i2c_client *client,
 190        const struct i2c_device_id *id)
 191{
 192        struct sht21 *sht21;
 193        int err;
 194
 195        if (!i2c_check_functionality(client->adapter,
 196                                     I2C_FUNC_SMBUS_WORD_DATA)) {
 197                dev_err(&client->dev,
 198                        "adapter does not support SMBus word transactions\n");
 199                return -ENODEV;
 200        }
 201
 202        sht21 = kzalloc(sizeof(*sht21), GFP_KERNEL);
 203        if (!sht21) {
 204                dev_dbg(&client->dev, "kzalloc failed\n");
 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                goto fail_free;
 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);
 229fail_free:
 230        kfree(sht21);
 231
 232        return err;
 233}
 234
 235/**
 236 * sht21_remove() - remove device
 237 * @client: I2C client device
 238 */
 239static int __devexit sht21_remove(struct i2c_client *client)
 240{
 241        struct sht21 *sht21 = i2c_get_clientdata(client);
 242
 243        hwmon_device_unregister(sht21->hwmon_dev);
 244        sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
 245        kfree(sht21);
 246
 247        return 0;
 248}
 249
 250/* Device ID table */
 251static const struct i2c_device_id sht21_id[] = {
 252        { "sht21", 0 },
 253        { }
 254};
 255MODULE_DEVICE_TABLE(i2c, sht21_id);
 256
 257static struct i2c_driver sht21_driver = {
 258        .driver.name = "sht21",
 259        .probe       = sht21_probe,
 260        .remove      = __devexit_p(sht21_remove),
 261        .id_table    = sht21_id,
 262};
 263
 264module_i2c_driver(sht21_driver);
 265
 266MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
 267MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
 268MODULE_LICENSE("GPL");
 269
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