/* Honeywell HIH-6130/HIH-6131 humidity and temperature sensor driver
   *
   * Copyright (C) 2012 Iain Paton <ipaton0@gmail.com>
   *
   * heavily based on the sht21 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 sheets available (2012-06-22) at
   * http://sensing.honeywell.com/index.php?ci_id=3106&la_id=1&defId=44872
   */
  
  #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/delay.h>
  #include <linux/jiffies.h>
  
  /**
   * struct hih6130 - HIH-6130 device specific data
   * @hwmon_dev: device registered with hwmon
   * @lock: mutex to protect measurement values
   * @valid: only false before first measurement is taken
   * @last_update: time of last update (jiffies)
   * @temperature: cached temperature measurement value
   * @humidity: cached humidity measurement value
   * @write_length: length for I2C measurement request
   */
  struct hih6130 {
  	struct i2c_client *client;
  	struct mutex lock;
  	bool valid;
  	unsigned long last_update;
  	int temperature;
  	int humidity;
  	size_t write_length;
  };
  
  /**
   * hih6130_temp_ticks_to_millicelsius() - convert raw temperature ticks to
   * milli celsius
   * @ticks: temperature ticks value received from sensor
   */
  static inline int hih6130_temp_ticks_to_millicelsius(int ticks)
  {
  	ticks = ticks >> 2;
  	/*
  	 * from data sheet section 5.0
  	 * Formula T = ( ticks / ( 2^14 - 2 ) ) * 165 -40
  	 */
  	return (DIV_ROUND_CLOSEST(ticks * 1650, 16382) - 400) * 100;
  }
  
  /**
   * hih6130_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 hih6130_rh_ticks_to_per_cent_mille(int ticks)
  {
  	ticks &= ~0xC000; /* clear status bits */
  	/*
  	 * from data sheet section 4.0
  	 * Formula RH = ( ticks / ( 2^14 -2 ) ) * 100
  	 */
  	return DIV_ROUND_CLOSEST(ticks * 1000, 16382) * 100;
  }
  
  /**
   * hih6130_update_measurements() - get updated measurements from device
   * @dev: device
   *
   * Returns 0 on success, else negative errno.
   */
  static int hih6130_update_measurements(struct device *dev)
  {
  	struct hih6130 *hih6130 = dev_get_drvdata(dev);
  	struct i2c_client *client = hih6130->client;
  	int ret = 0;
  	int t;
  	unsigned char tmp[4];
  	struct i2c_msg msgs[1] = {
  		{
  			.addr = client->addr,
  			.flags = I2C_M_RD,
  			.len = 4,
  			.buf = tmp,
  		}
  	};
  
  	mutex_lock(&hih6130->lock);
  
  	/*
  	 * While the measurement can be completed in ~40ms the sensor takes
  	 * much longer to react to a change in external conditions. How quickly
  	 * it reacts depends on airflow and other factors outwith our control.
  	 * The datasheet specifies maximum 'Response time' for humidity at 8s
  	 * and temperature at 30s under specified conditions.
  	 * We therefore choose to only read the sensor at most once per second.
  	 * This trades off pointless activity polling the sensor much faster
  	 * than it can react against better response times in conditions more
  	 * favourable than specified in the datasheet.
  	 */
  	if (time_after(jiffies, hih6130->last_update + HZ) || !hih6130->valid) {
  
  		/*
  		 * Write to slave address to request a measurement.
  		 * According with the datasheet it should be with no data, but
  		 * for systems with I2C bus drivers that do not allow zero
  		 * length packets we write one dummy byte to allow sensor
  		 * measurements on them.
  		 */
  		tmp[0] = 0;
  		ret = i2c_master_send(client, tmp, hih6130->write_length);
  		if (ret < 0)
  			goto out;
  
  		/* measurement cycle time is ~36.65msec */
  		msleep(40);
  
  		ret = i2c_transfer(client->adapter, msgs, 1);
  		if (ret < 0)
  			goto out;
  
  		if ((tmp[0] & 0xC0) != 0) {
  			dev_err(&client->dev, "Error while reading measurement result
  ");
  			ret = -EIO;
  			goto out;
  		}
  
  		t = (tmp[0] << 8) + tmp[1];
  		hih6130->humidity = hih6130_rh_ticks_to_per_cent_mille(t);
  
  		t = (tmp[2] << 8) + tmp[3];
  		hih6130->temperature = hih6130_temp_ticks_to_millicelsius(t);
  
  		hih6130->last_update = jiffies;
  		hih6130->valid = true;
  	}
  out:
  	mutex_unlock(&hih6130->lock);
  
  	return ret >= 0 ? 0 : ret;
  }
  
  /**
   * hih6130_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 hih6130_show_temperature(struct device *dev,
  					struct device_attribute *attr,
  					char *buf)
  {
  	struct hih6130 *hih6130 = dev_get_drvdata(dev);
  	int ret;
  
  	ret = hih6130_update_measurements(dev);
  	if (ret < 0)
  		return ret;
  	return sprintf(buf, "%d
  ", hih6130->temperature);
  }
  
  /**
   * hih6130_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 hih6130_show_humidity(struct device *dev,
  				     struct device_attribute *attr, char *buf)
  {
  	struct hih6130 *hih6130 = dev_get_drvdata(dev);
  	int ret;
  
  	ret = hih6130_update_measurements(dev);
  	if (ret < 0)
  		return ret;
  	return sprintf(buf, "%d
  ", hih6130->humidity);
  }
  
  /* sysfs attributes */
  static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO, hih6130_show_temperature,
  	NULL, 0);
  static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO, hih6130_show_humidity,
  	NULL, 0);
  
  static struct attribute *hih6130_attrs[] = {
  	&sensor_dev_attr_temp1_input.dev_attr.attr,
  	&sensor_dev_attr_humidity1_input.dev_attr.attr,
  	NULL
  };
  
  ATTRIBUTE_GROUPS(hih6130);
  
  static int hih6130_probe(struct i2c_client *client,
  				   const struct i2c_device_id *id)
  {
  	struct device *dev = &client->dev;
  	struct hih6130 *hih6130;
  	struct device *hwmon_dev;
  
  	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
  		dev_err(&client->dev, "adapter does not support true I2C
  ");
  		return -ENODEV;
  	}
  
  	hih6130 = devm_kzalloc(dev, sizeof(*hih6130), GFP_KERNEL);
  	if (!hih6130)
  		return -ENOMEM;
  
  	hih6130->client = client;
  	mutex_init(&hih6130->lock);
  
  	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_QUICK))
  		hih6130->write_length = 1;
  
  	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
  							   hih6130,
  							   hih6130_groups);
  	return PTR_ERR_OR_ZERO(hwmon_dev);
  }
  
  /* Device ID table */
  static const struct i2c_device_id hih6130_id[] = {
  	{ "hih6130", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, hih6130_id);
  
  static struct i2c_driver hih6130_driver = {
  	.driver.name = "hih6130",
  	.probe       = hih6130_probe,
  	.id_table    = hih6130_id,
  };
  
  module_i2c_driver(hih6130_driver);
  
  MODULE_AUTHOR("Iain Paton <ipaton0@gmail.com>");
  MODULE_DESCRIPTION("Honeywell HIH-6130 humidity and temperature sensor driver");
  MODULE_LICENSE("GPL");