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hwmon: driver for Sensirion SHT21 humidity and temperature sensor 

Signed-off-by: Urs Fleisch <urs.fleisch@sensirion.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
This commit is contained in:
Urs Fleisch 2011-01-07 07:15:39 +00:00 committed by Guenter Roeck
parent c6c2c1636e
commit 430400b863
4 changed files with 367 additions and 0 deletions
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49
Documentation/hwmon/sht21 Normal file
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@ -0,0 +1,49 @@
Kernel driver sht21
===================
Supported chips:
* Sensirion SHT21
Prefix: 'sht21'
Addresses scanned: none
Datasheet: Publicly available at the Sensirion website
http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT21.pdf
* Sensirion SHT25
Prefix: 'sht21'
Addresses scanned: none
Datasheet: Publicly available at the Sensirion website
http://www.sensirion.com/en/pdf/product_information/Datasheet-humidity-sensor-SHT25.pdf
Author:
Urs Fleisch <urs.fleisch@sensirion.com>
Description
-----------
The SHT21 and SHT25 are humidity and temperature sensors in a DFN package of
only 3 x 3 mm footprint and 1.1 mm height. The difference between the two
devices is the higher level of precision of the SHT25 (1.8% relative humidity,
0.2 degree Celsius) compared with the SHT21 (2.0% relative humidity,
0.3 degree Celsius).
The devices communicate with the I2C protocol. All sensors are set to the same
I2C address 0x40, so an entry with I2C_BOARD_INFO("sht21", 0x40) can be used
in the board setup code.
sysfs-Interface
---------------
temp1_input - temperature input
humidity1_input - humidity input
Notes
-----
The driver uses the default resolution settings of 12 bit for humidity and 14
bit for temperature, which results in typical measurement times of 22 ms for
humidity and 66 ms for temperature. To keep self heating below 0.1 degree
Celsius, the device should not be active for more than 10% of the time,
e.g. maximum two measurements per second at the given resolution.
Different resolutions, the on-chip heater, using the CRC checksum and reading
the serial number are not supported yet.

10
drivers/hwmon/Kconfig
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@ -734,6 +734,16 @@ config SENSORS_SHT15
This driver can also be built as a module. If so, the module
will be called sht15.
config SENSORS_SHT21
tristate "Sensiron humidity and temperature sensors. SHT21 and compat."
depends on I2C
help
If you say yes here you get support for the Sensiron SHT21, SHT25
humidity and temperature sensors.
This driver can also be built as a module. If so, the module
will be called sht21.
config SENSORS_S3C
tristate "Samsung built-in ADC"
depends on S3C_ADC

1
drivers/hwmon/Makefile
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@ -90,6 +90,7 @@ obj-$(CONFIG_SENSORS_PC87427) += pc87427.o
obj-$(CONFIG_SENSORS_PCF8591) += pcf8591.o
obj-$(CONFIG_SENSORS_S3C) += s3c-hwmon.o
obj-$(CONFIG_SENSORS_SHT15) += sht15.o
obj-$(CONFIG_SENSORS_SHT21) += sht21.o
obj-$(CONFIG_SENSORS_SIS5595) += sis5595.o
obj-$(CONFIG_SENSORS_SMM665) += smm665.o
obj-$(CONFIG_SENSORS_SMSC47B397)+= smsc47b397.o

307
drivers/hwmon/sht21.c Normal file
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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>
/* 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 device *hwmon_dev;
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_read_word_data() - read word from register
* @client: I2C client device
* @reg: I2C command byte
*
* Returns value, negative errno on error.
*/
static inline int sht21_read_word_data(struct i2c_client *client, u8 reg)
{
int ret = i2c_smbus_read_word_data(client, reg);
if (ret < 0)
return ret;
/*
* SMBus specifies low byte first, but the SHT21 returns MSB
* first, so we have to swab16 the values
*/
return swab16(ret);
}
/**
* sht21_update_measurements() - get updated measurements from device
* @client: I2C client device
*
* Returns 0 on success, else negative errno.
*/
static int sht21_update_measurements(struct i2c_client *client)
{
int ret = 0;
struct sht21 *sht21 = i2c_get_clientdata(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 = sht21_read_word_data(client, SHT21_TRIG_T_MEASUREMENT_HM);
if (ret < 0)
goto out;
sht21->temperature = sht21_temp_ticks_to_millicelsius(ret);
ret = sht21_read_word_data(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 i2c_client *client = to_i2c_client(dev);
struct sht21 *sht21 = i2c_get_clientdata(client);
int ret = sht21_update_measurements(client);
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 i2c_client *client = to_i2c_client(dev);
struct sht21 *sht21 = i2c_get_clientdata(client);
int ret = sht21_update_measurements(client);
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_attributes[] = {
&sensor_dev_attr_temp1_input.dev_attr.attr,
&sensor_dev_attr_humidity1_input.dev_attr.attr,
NULL
};
static const struct attribute_group sht21_attr_group = {
.attrs = sht21_attributes,
};
/**
* sht21_probe() - probe device
* @client: I2C client device
* @id: device ID
*
* Called by the I2C core when an entry in the ID table matches a
* device's name.
* Returns 0 on success.
*/
static int __devinit sht21_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct sht21 *sht21;
int err;
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 = kzalloc(sizeof(*sht21), GFP_KERNEL);
if (!sht21) {
dev_dbg(&client->dev, "kzalloc failed\n");
return -ENOMEM;
}
i2c_set_clientdata(client, sht21);
mutex_init(&sht21->lock);
err = sysfs_create_group(&client->dev.kobj, &sht21_attr_group);
if (err) {
dev_dbg(&client->dev, "could not create sysfs files\n");
goto fail_free;
}
sht21->hwmon_dev = hwmon_device_register(&client->dev);
if (IS_ERR(sht21->hwmon_dev)) {
dev_dbg(&client->dev, "unable to register hwmon device\n");
err = PTR_ERR(sht21->hwmon_dev);
goto fail_remove_sysfs;
}
dev_info(&client->dev, "initialized\n");
return 0;
fail_remove_sysfs:
sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
fail_free:
kfree(sht21);
return err;
}
/**
* sht21_remove() - remove device
* @client: I2C client device
*/
static int __devexit sht21_remove(struct i2c_client *client)
{
struct sht21 *sht21 = i2c_get_clientdata(client);
hwmon_device_unregister(sht21->hwmon_dev);
sysfs_remove_group(&client->dev.kobj, &sht21_attr_group);
kfree(sht21);
return 0;
}
/* 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,
.remove = __devexit_p(sht21_remove),
.id_table = sht21_id,
};
/**
* sht21_init() - initialize driver
*
* Called when kernel is booted or module is inserted.
* Returns 0 on success.
*/
static int __init sht21_init(void)
{
return i2c_add_driver(&sht21_driver);
}
module_init(sht21_init);
/**
* sht21_init() - clean up driver
*
* Called when module is removed.
*/
static void __exit sht21_exit(void)
{
i2c_del_driver(&sht21_driver);
}
module_exit(sht21_exit);
MODULE_AUTHOR("Urs Fleisch <urs.fleisch@sensirion.com>");
MODULE_DESCRIPTION("Sensirion SHT21 humidity and temperature sensor driver");
MODULE_LICENSE("GPL");