226 lines
6.3 KiB
C
226 lines
6.3 KiB
C
/* Sensirion SHT21 humidity and temperature sensor driver
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*
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* Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
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*
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* Data sheet available (5/2010) at
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* http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
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*/
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/slab.h>
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#include <linux/i2c.h>
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#include <linux/hwmon.h>
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#include <linux/hwmon-sysfs.h>
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#include <linux/err.h>
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#include <linux/mutex.h>
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#include <linux/device.h>
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#include <linux/jiffies.h>
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/* I2C command bytes */
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#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
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#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
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/**
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* struct sht21 - SHT21 device specific data
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* @hwmon_dev: device registered with hwmon
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* @lock: mutex to protect measurement values
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* @valid: only 0 before first measurement is taken
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* @last_update: time of last update (jiffies)
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* @temperature: cached temperature measurement value
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* @humidity: cached humidity measurement value
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*/
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struct sht21 {
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struct i2c_client *client;
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struct mutex lock;
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char valid;
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unsigned long last_update;
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int temperature;
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int humidity;
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};
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/**
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* sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
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* milli celsius
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* @ticks: temperature ticks value received from sensor
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*/
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static inline int sht21_temp_ticks_to_millicelsius(int ticks)
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{
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ticks &= ~0x0003; /* clear status bits */
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/*
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* Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
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* optimized for integer fixed point (3 digits) arithmetic
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*/
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return ((21965 * ticks) >> 13) - 46850;
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}
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/**
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* sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
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* one-thousandths of a percent relative humidity
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* @ticks: humidity ticks value received from sensor
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*/
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static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
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{
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ticks &= ~0x0003; /* clear status bits */
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/*
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* Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
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* optimized for integer fixed point (3 digits) arithmetic
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*/
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return ((15625 * ticks) >> 13) - 6000;
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}
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/**
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* sht21_update_measurements() - get updated measurements from device
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* @dev: device
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*
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* Returns 0 on success, else negative errno.
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*/
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static int sht21_update_measurements(struct device *dev)
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{
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int ret = 0;
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struct sht21 *sht21 = dev_get_drvdata(dev);
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struct i2c_client *client = sht21->client;
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mutex_lock(&sht21->lock);
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/*
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* Data sheet 2.4:
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* SHT2x should not be active for more than 10% of the time - e.g.
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* maximum two measurements per second at 12bit accuracy shall be made.
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*/
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if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
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ret = i2c_smbus_read_word_swapped(client,
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SHT21_TRIG_T_MEASUREMENT_HM);
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if (ret < 0)
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goto out;
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sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
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ret = i2c_smbus_read_word_swapped(client,
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SHT21_TRIG_RH_MEASUREMENT_HM);
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if (ret < 0)
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goto out;
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sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
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sht21->last_update = jiffies;
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sht21->valid = 1;
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}
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out:
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mutex_unlock(&sht21->lock);
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return ret >= 0 ? 0 : ret;
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}
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/**
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* sht21_show_temperature() - show temperature measurement value in sysfs
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* @dev: device
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* @attr: device attribute
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* @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
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*
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* Will be called on read access to temp1_input sysfs attribute.
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* Returns number of bytes written into buffer, negative errno on error.
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*/
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static ssize_t sht21_show_temperature(struct device *dev,
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struct device_attribute *attr,
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char *buf)
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{
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struct sht21 *sht21 = dev_get_drvdata(dev);
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int ret;
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ret = sht21_update_measurements(dev);
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if (ret < 0)
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return ret;
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return sprintf(buf, "%d\n", sht21->temperature);
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}
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/**
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* sht21_show_humidity() - show humidity measurement value in sysfs
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* @dev: device
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* @attr: device attribute
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* @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
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*
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* Will be called on read access to humidity1_input sysfs attribute.
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* Returns number of bytes written into buffer, negative errno on error.
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*/
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static ssize_t sht21_show_humidity(struct device *dev,
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struct device_attribute *attr,
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char *buf)
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{
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struct sht21 *sht21 = dev_get_drvdata(dev);
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int ret;
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ret = sht21_update_measurements(dev);
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if (ret < 0)
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return ret;
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return sprintf(buf, "%d\n", sht21->humidity);
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}
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/* sysfs attributes */
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static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
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NULL, 0);
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static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
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NULL, 0);
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static struct attribute *sht21_attrs[] = {
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&sensor_dev_attr_temp1_input.dev_attr.attr,
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&sensor_dev_attr_humidity1_input.dev_attr.attr,
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NULL
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};
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ATTRIBUTE_GROUPS(sht21);
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static int sht21_probe(struct i2c_client *client,
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const struct i2c_device_id *id)
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{
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struct device *dev = &client->dev;
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struct device *hwmon_dev;
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struct sht21 *sht21;
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if (!i2c_check_functionality(client->adapter,
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I2C_FUNC_SMBUS_WORD_DATA)) {
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dev_err(&client->dev,
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"adapter does not support SMBus word transactions\n");
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return -ENODEV;
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}
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sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
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if (!sht21)
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return -ENOMEM;
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sht21->client = client;
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mutex_init(&sht21->lock);
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hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
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sht21, sht21_groups);
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return PTR_ERR_OR_ZERO(hwmon_dev);
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}
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/* Device ID table */
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static const struct i2c_device_id sht21_id[] = {
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{ "sht21", 0 },
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{ }
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};
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MODULE_DEVICE_TABLE(i2c, sht21_id);
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static struct i2c_driver sht21_driver = {
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.driver.name = "sht21",
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.probe = sht21_probe,
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.id_table = sht21_id,
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};
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module_i2c_driver(sht21_driver);
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MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
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MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
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MODULE_LICENSE("GPL");
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