/*
   * Measurement Specialties HTU21D humidity and temperature sensor driver
   *
   * Copyright (C) 2013 William Markezana <william.markezana@meas-spec.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.
   *
   */
  
  #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>
  
  /* HTU21 Commands */
  #define HTU21_T_MEASUREMENT_HM	0xE3
  #define HTU21_RH_MEASUREMENT_HM	0xE5
  
  struct htu21 {
  	struct device *hwmon_dev;
  	struct mutex lock;
  	bool valid;
  	unsigned long last_update;
  	int temperature;
  	int humidity;
  };
  
  static inline int htu21_temp_ticks_to_millicelsius(int ticks)
  {
  	ticks &= ~0x0003; /* clear status bits */
  	/*
  	 * Formula T = -46.85 + 175.72 * ST / 2^16 from datasheet p14,
  	 * optimized for integer fixed point (3 digits) arithmetic
  	 */
  	return ((21965 * ticks) >> 13) - 46850;
  }
  
  static inline int htu21_rh_ticks_to_per_cent_mille(int ticks)
  {
  	ticks &= ~0x0003; /* clear status bits */
  	/*
  	 * Formula RH = -6 + 125 * SRH / 2^16 from datasheet p14,
  	 * optimized for integer fixed point (3 digits) arithmetic
  	 */
  	return ((15625 * ticks) >> 13) - 6000;
  }
  
  static int htu21_update_measurements(struct i2c_client *client)
  {
  	int ret = 0;
  	struct htu21 *htu21 = i2c_get_clientdata(client);
  
  	mutex_lock(&htu21->lock);
  
  	if (time_after(jiffies, htu21->last_update + HZ / 2) ||
  	    !htu21->valid) {
  		ret = i2c_smbus_read_word_swapped(client,
  						  HTU21_T_MEASUREMENT_HM);
  		if (ret < 0)
  			goto out;
  		htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
  		ret = i2c_smbus_read_word_swapped(client,
  						  HTU21_RH_MEASUREMENT_HM);
  		if (ret < 0)
  			goto out;
  		htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
  		htu21->last_update = jiffies;
  		htu21->valid = true;
  	}
  out:
  	mutex_unlock(&htu21->lock);
  
  	return ret >= 0 ? 0 : ret;
  }
  
  static ssize_t htu21_show_temperature(struct device *dev,
  				      struct device_attribute *attr, char *buf)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	struct htu21 *htu21 = i2c_get_clientdata(client);
  	int ret = htu21_update_measurements(client);
  	if (ret < 0)
  		return ret;
  	return sprintf(buf, "%d
  ", htu21->temperature);
  }
  
  static ssize_t htu21_show_humidity(struct device *dev,
  				   struct device_attribute *attr, char *buf)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	struct htu21 *htu21 = i2c_get_clientdata(client);
  	int ret = htu21_update_measurements(client);
  	if (ret < 0)
  		return ret;
  	return sprintf(buf, "%d
  ", htu21->humidity);
  }
  
  static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
  			  htu21_show_temperature, NULL, 0);
  static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
  			  htu21_show_humidity, NULL, 0);
  
  static struct attribute *htu21_attributes[] = {
  	&sensor_dev_attr_temp1_input.dev_attr.attr,
  	&sensor_dev_attr_humidity1_input.dev_attr.attr,
  	NULL
  };
  
  static const struct attribute_group htu21_group = {
  	.attrs = htu21_attributes,
  };
  
  static int htu21_probe(struct i2c_client *client,
  		       const struct i2c_device_id *id)
  {
  	struct htu21 *htu21;
  	int err;
  
  	if (!i2c_check_functionality(client->adapter,
  				     I2C_FUNC_SMBUS_READ_WORD_DATA)) {
  		dev_err(&client->dev,
  			"adapter does not support SMBus word transactions
  ");
  		return -ENODEV;
  	}
  
  	htu21 = devm_kzalloc(&client->dev, sizeof(*htu21), GFP_KERNEL);
  	if (!htu21)
  		return -ENOMEM;
  
  	i2c_set_clientdata(client, htu21);
  
  	mutex_init(&htu21->lock);
  
  	err = sysfs_create_group(&client->dev.kobj, &htu21_group);
  	if (err) {
  		dev_dbg(&client->dev, "could not create sysfs files
  ");
  		return err;
  	}
  	htu21->hwmon_dev = hwmon_device_register(&client->dev);
  	if (IS_ERR(htu21->hwmon_dev)) {
  		dev_dbg(&client->dev, "unable to register hwmon device
  ");
  		err = PTR_ERR(htu21->hwmon_dev);
  		goto error;
  	}
  
  	dev_info(&client->dev, "initialized
  ");
  
  	return 0;
  
  error:
  	sysfs_remove_group(&client->dev.kobj, &htu21_group);
  	return err;
  }
  
  static int htu21_remove(struct i2c_client *client)
  {
  	struct htu21 *htu21 = i2c_get_clientdata(client);
  
  	hwmon_device_unregister(htu21->hwmon_dev);
  	sysfs_remove_group(&client->dev.kobj, &htu21_group);
  
  	return 0;
  }
  
  static const struct i2c_device_id htu21_id[] = {
  	{ "htu21", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, htu21_id);
  
  static struct i2c_driver htu21_driver = {
  	.class = I2C_CLASS_HWMON,
  	.driver = {
  		.name	= "htu21",
  	},
  	.probe       = htu21_probe,
  	.remove      = htu21_remove,
  	.id_table    = htu21_id,
  };
  
  module_i2c_driver(htu21_driver);
  
  MODULE_AUTHOR("William Markezana <william.markezana@meas-spec.com>");
  MODULE_DESCRIPTION("MEAS HTU21D humidity and temperature sensor driver");
  MODULE_LICENSE("GPL");