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+/*
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+ * Measurement Specialties HTU21D humidity and temperature sensor driver
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+ *
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+ * Copyright (C) 2013 William Markezana <william.markezana@meas-spec.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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+ */
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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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+
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+/* HTU21 Commands */
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+#define HTU21_T_MEASUREMENT_HM 0xE3
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+#define HTU21_RH_MEASUREMENT_HM 0xE5
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+
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+struct htu21 {
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+ struct device *hwmon_dev;
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+ struct mutex lock;
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+ bool 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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+static inline int htu21_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 datasheet p14,
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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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+static inline int htu21_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 datasheet p14,
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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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+static int htu21_update_measurements(struct i2c_client *client)
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+{
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+ int ret = 0;
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+ struct htu21 *htu21 = i2c_get_clientdata(client);
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+
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+ mutex_lock(&htu21->lock);
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+
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+ if (time_after(jiffies, htu21->last_update + HZ / 2) ||
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+ !htu21->valid) {
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+ ret = i2c_smbus_read_word_swapped(client,
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+ HTU21_T_MEASUREMENT_HM);
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+ if (ret < 0)
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+ goto out;
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+ htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
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+ ret = i2c_smbus_read_word_swapped(client,
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+ HTU21_RH_MEASUREMENT_HM);
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+ if (ret < 0)
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+ goto out;
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+ htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
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+ htu21->last_update = jiffies;
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+ htu21->valid = true;
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+ }
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+out:
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+ mutex_unlock(&htu21->lock);
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+
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+ return ret >= 0 ? 0 : ret;
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+}
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+
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+static ssize_t htu21_show_temperature(struct device *dev,
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+ struct device_attribute *attr, char *buf)
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+{
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+ struct i2c_client *client = to_i2c_client(dev);
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+ struct htu21 *htu21 = i2c_get_clientdata(client);
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+ int ret = htu21_update_measurements(client);
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+ if (ret < 0)
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+ return ret;
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+ return sprintf(buf, "%d\n", htu21->temperature);
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+}
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+
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+static ssize_t htu21_show_humidity(struct device *dev,
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+ struct device_attribute *attr, char *buf)
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+{
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+ struct i2c_client *client = to_i2c_client(dev);
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+ struct htu21 *htu21 = i2c_get_clientdata(client);
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+ int ret = htu21_update_measurements(client);
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+ if (ret < 0)
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+ return ret;
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+ return sprintf(buf, "%d\n", htu21->humidity);
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+}
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+
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+static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
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+ htu21_show_temperature, NULL, 0);
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+static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
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+ htu21_show_humidity, NULL, 0);
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+
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+static struct attribute *htu21_attributes[] = {
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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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+
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+static const struct attribute_group htu21_group = {
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+ .attrs = htu21_attributes,
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+};
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+
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+static int htu21_probe(struct i2c_client *client,
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+ const struct i2c_device_id *id)
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+{
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+ struct htu21 *htu21;
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+ int err;
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+
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+ if (!i2c_check_functionality(client->adapter,
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+ I2C_FUNC_SMBUS_READ_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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+
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+ htu21 = devm_kzalloc(&client->dev, sizeof(*htu21), GFP_KERNEL);
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+ if (!htu21)
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+ return -ENOMEM;
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+
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+ i2c_set_clientdata(client, htu21);
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+
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+ mutex_init(&htu21->lock);
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+
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+ err = sysfs_create_group(&client->dev.kobj, &htu21_group);
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+ if (err) {
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+ dev_dbg(&client->dev, "could not create sysfs files\n");
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+ return err;
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+ }
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+ htu21->hwmon_dev = hwmon_device_register(&client->dev);
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+ if (IS_ERR(htu21->hwmon_dev)) {
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+ dev_dbg(&client->dev, "unable to register hwmon device\n");
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+ err = PTR_ERR(htu21->hwmon_dev);
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+ goto error;
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+ }
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+
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+ dev_info(&client->dev, "initialized\n");
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+
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+ return 0;
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+
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+error:
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+ sysfs_remove_group(&client->dev.kobj, &htu21_group);
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+ return err;
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+}
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+
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+static int htu21_remove(struct i2c_client *client)
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+{
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+ struct htu21 *htu21 = i2c_get_clientdata(client);
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+
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+ hwmon_device_unregister(htu21->hwmon_dev);
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+ sysfs_remove_group(&client->dev.kobj, &htu21_group);
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+
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+ return 0;
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+}
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+
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+static const struct i2c_device_id htu21_id[] = {
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+ { "htu21", 0 },
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+ { }
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+};
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+MODULE_DEVICE_TABLE(i2c, htu21_id);
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+
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+static struct i2c_driver htu21_driver = {
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+ .class = I2C_CLASS_HWMON,
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+ .driver = {
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+ .name = "htu21",
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+ },
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+ .probe = htu21_probe,
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+ .remove = htu21_remove,
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+ .id_table = htu21_id,
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+};
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+
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+module_i2c_driver(htu21_driver);
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+
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+MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
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+MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
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+MODULE_LICENSE("GPL");
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