/* 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
  ", 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
  ", 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
  ");
  		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");