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/* Sensirion SHT21 humidity and temperature sensor driver
*
* Copyright (C) 2010 Urs Fleisch <urs.fleisch@sensirion.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.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA
*
* Data sheet available (5/2010) at
* http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
*/
#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>
/* I2C command bytes */
#define SHT21_TRIG_T_MEASUREMENT_HM 0xe3
#define SHT21_TRIG_RH_MEASUREMENT_HM 0xe5
/**
* struct sht21 - SHT21 device specific data
* @hwmon_dev: device registered with hwmon
* @lock: mutex to protect measurement values
* @valid: only 0 before first measurement is taken
* @last_update: time of last update (jiffies)
* @temperature: cached temperature measurement value
* @humidity: cached humidity measurement value
*/
struct sht21 {
struct i2c_client *client;
struct mutex lock;
char valid;
unsigned long last_update;
int temperature;
int humidity;
};
/**
* sht21_temp_ticks_to_millicelsius() - convert raw temperature ticks to
* milli celsius
* @ticks: temperature ticks value received from sensor
*/
static inline int sht21_temp_ticks_to_millicelsius(int ticks)
{
ticks &= ~0x0003; /* clear status bits */
/*
* Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
* optimized for integer fixed point (3 digits) arithmetic
*/
return ((21965 * ticks) >> 13) - 46850;
}
/**
* sht21_rh_ticks_to_per_cent_mille() - convert raw humidity ticks to
* one-thousandths of a percent relative humidity
* @ticks: humidity ticks value received from sensor
*/
static inline int sht21_rh_ticks_to_per_cent_mille(int ticks)
{
ticks &= ~0x0003; /* clear status bits */
/*
* Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
* optimized for integer fixed point (3 digits) arithmetic
*/
return ((15625 * ticks) >> 13) - 6000;
}
/**
* sht21_update_measurements() - get updated measurements from device
* @dev: device
*
* Returns 0 on success, else negative errno.
*/
static int sht21_update_measurements(struct device *dev)
{
int ret = 0;
struct sht21 *sht21 = dev_get_drvdata(dev);
struct i2c_client *client = sht21->client;
mutex_lock(&sht21->lock);
/*
* Data sheet 2.4:
* SHT2x should not be active for more than 10% of the time - e.g.
* maximum two measurements per second at 12bit accuracy shall be made.
*/
if (time_after(jiffies, sht21->last_update + HZ / 2) || !sht21->valid) {
ret = i2c_smbus_read_word_swapped(client,
SHT21_TRIG_T_MEASUREMENT_HM);
if (ret < 0)
goto out;
sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
ret = i2c_smbus_read_word_swapped(client,
SHT21_TRIG_RH_MEASUREMENT_HM);
if (ret < 0)
goto out;
sht21->humidity = sht21_rh_ticks_to_per_cent_mille(ret);
sht21->last_update = jiffies;
sht21->valid = 1;
}
out:
mutex_unlock(&sht21->lock);
return ret >= 0 ? 0 : ret;
}
/**
* sht21_show_temperature() - show temperature measurement value in sysfs
* @dev: device
* @attr: device attribute
* @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
*
* Will be called on read access to temp1_input sysfs attribute.
* Returns number of bytes written into buffer, negative errno on error.
*/
static ssize_t sht21_show_temperature(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct sht21 *sht21 = dev_get_drvdata(dev);
int ret;
ret = sht21_update_measurements(dev);
if (ret < 0)
return ret;
return sprintf(buf, "%d\n", sht21->temperature);
}
/**
* sht21_show_humidity() - show humidity measurement value in sysfs
* @dev: device
* @attr: device attribute
* @buf: sysfs buffer (PAGE_SIZE) where measurement values are written to
*
* Will be called on read access to humidity1_input sysfs attribute.
* Returns number of bytes written into buffer, negative errno on error.
*/
static ssize_t sht21_show_humidity(struct device *dev,
struct device_attribute *attr,
char *buf)
{
struct sht21 *sht21 = dev_get_drvdata(dev);
int ret;
ret = sht21_update_measurements(dev);
if (ret < 0)
return ret;
return sprintf(buf, "%d\n", sht21->humidity);
}
/* sysfs attributes */
static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, sht21_show_temperature,
NULL, 0);
static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, sht21_show_humidity,
NULL, 0);
static struct attribute *sht21_attrs[] = {
&sensor_dev_attr_temp1_input.dev_attr.attr,
&sensor_dev_attr_humidity1_input.dev_attr.attr,
NULL
};
ATTRIBUTE_GROUPS(sht21);
static int sht21_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct device *dev = &client->dev;
struct device *hwmon_dev;
struct sht21 *sht21;
if (!i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_WORD_DATA)) {
dev_err(&client->dev,
"adapter does not support SMBus word transactions\n");
return -ENODEV;
}
sht21 = devm_kzalloc(dev, sizeof(*sht21), GFP_KERNEL);
if (!sht21)
return -ENOMEM;
sht21->client = client;
mutex_init(&sht21->lock);
hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
sht21, sht21_groups);
return PTR_ERR_OR_ZERO(hwmon_dev);
}
/* Device ID table */
static const struct i2c_device_id sht21_id[] = {
{ "sht21", 0 },
{ }
};
MODULE_DEVICE_TABLE(i2c, sht21_id);
static struct i2c_driver sht21_driver = {
.driver.name = "sht21",
.probe = sht21_probe,
.id_table = sht21_id,
};
module_i2c_driver(sht21_driver);
MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");
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