/* 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");