htu21.c
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/*
* Measurement Specialties HTU21D humidity and temperature sensor driver
*
* Copyright (C) 2013 William Markezana <william.markezana@meas-spec.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/i2c.h>
#include <linux/hwmon.h>
#include <linux/hwmon-sysfs.h>
#include <linux/err.h>
#include <linux/mutex.h>
#include <linux/device.h>
#include <linux/jiffies.h>
/* HTU21 Commands */
#define HTU21_T_MEASUREMENT_HM 0xE3
#define HTU21_RH_MEASUREMENT_HM 0xE5
struct htu21 {
struct i2c_client *client;
struct mutex lock;
bool valid;
unsigned long last_update;
int temperature;
int humidity;
};
static inline int htu21_temp_ticks_to_millicelsius(int ticks)
{
ticks &= ~0x0003; /* clear status bits */
/*
* Formula T = -46.85 + 175.72 * ST / 2^16 from datasheet p14,
* optimized for integer fixed point (3 digits) arithmetic
*/
return ((21965 * ticks) >> 13) - 46850;
}
static inline int htu21_rh_ticks_to_per_cent_mille(int ticks)
{
ticks &= ~0x0003; /* clear status bits */
/*
* Formula RH = -6 + 125 * SRH / 2^16 from datasheet p14,
* optimized for integer fixed point (3 digits) arithmetic
*/
return ((15625 * ticks) >> 13) - 6000;
}
static int htu21_update_measurements(struct device *dev)
{
struct htu21 *htu21 = dev_get_drvdata(dev);
struct i2c_client *client = htu21->client;
int ret = 0;
mutex_lock(&htu21->lock);
if (time_after(jiffies, htu21->last_update + HZ / 2) ||
!htu21->valid) {
ret = i2c_smbus_read_word_swapped(client,
HTU21_T_MEASUREMENT_HM);
if (ret < 0)
goto out;
htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
ret = i2c_smbus_read_word_swapped(client,
HTU21_RH_MEASUREMENT_HM);
if (ret < 0)
goto out;
htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
htu21->last_update = jiffies;
htu21->valid = true;
}
out:
mutex_unlock(&htu21->lock);
return ret >= 0 ? 0 : ret;
}
static ssize_t htu21_show_temperature(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct htu21 *htu21 = dev_get_drvdata(dev);
int ret;
ret = htu21_update_measurements(dev);
if (ret < 0)
return ret;
return sprintf(buf, "%d\n", htu21->temperature);
}
static ssize_t htu21_show_humidity(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct htu21 *htu21 = dev_get_drvdata(dev);
int ret;
ret = htu21_update_measurements(dev);
if (ret < 0)
return ret;
return sprintf(buf, "%d\n", htu21->humidity);
}
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
htu21_show_temperature, NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
htu21_show_humidity, NULL, 0);
static struct attribute *htu21_attrs[] = {
&sensor_dev_attr_temp1_input.dev_attr.attr,
&sensor_dev_attr_humidity1_input.dev_attr.attr,
NULL
};
ATTRIBUTE_GROUPS(htu21);
static int htu21_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct device *dev = &client->dev;
struct htu21 *htu21;
struct device *hwmon_dev;
if (!i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_READ_WORD_DATA)) {
dev_err(&client->dev,
"adapter does not support SMBus word transactions\n");
return -ENODEV;
}
htu21 = devm_kzalloc(dev, sizeof(*htu21), GFP_KERNEL);
if (!htu21)
return -ENOMEM;
htu21->client = client;
mutex_init(&htu21->lock);
hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
htu21,
htu21_groups);
return PTR_ERR_OR_ZERO(hwmon_dev);
}
static const struct i2c_device_id htu21_id[] = {
{ "htu21", 0 },
{ }
};
MODULE_DEVICE_TABLE(i2c, htu21_id);
static struct i2c_driver htu21_driver = {
.class = I2C_CLASS_HWMON,
.driver = {
.name = "htu21",
},
.probe = htu21_probe,
.id_table = htu21_id,
};
module_i2c_driver(htu21_driver);
MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
MODULE_LICENSE("GPL");