diff options
Diffstat (limited to 'drivers/hwmon/sht21.c')
| -rw-r--r-- | drivers/hwmon/sht21.c | 226 |
1 files changed, 226 insertions, 0 deletions
diff --git a/drivers/hwmon/sht21.c b/drivers/hwmon/sht21.c new file mode 100644 index 000000000..84cdb1cf0 --- /dev/null +++ b/drivers/hwmon/sht21.c @@ -0,0 +1,226 @@ +/* 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"); |