/* Sensirion SHTC1 humidity and temperature sensor driver
   *
   * Copyright (C) 2014 Sensirion AG, Switzerland
   * Author: Johannes Winkelmann <johannes.winkelmann@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.
   *
   */
  
  #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/delay.h>
  #include <linux/platform_data/shtc1.h>
  
  /* commands (high precision mode) */
  static const unsigned char shtc1_cmd_measure_blocking_hpm[]    = { 0x7C, 0xA2 };
  static const unsigned char shtc1_cmd_measure_nonblocking_hpm[] = { 0x78, 0x66 };
  
  /* commands (low precision mode) */
  static const unsigned char shtc1_cmd_measure_blocking_lpm[]    = { 0x64, 0x58 };
  static const unsigned char shtc1_cmd_measure_nonblocking_lpm[] = { 0x60, 0x9c };
  
  /* command for reading the ID register */
  static const unsigned char shtc1_cmd_read_id_reg[]	       = { 0xef, 0xc8 };
  
  /* constants for reading the ID register */
  #define SHTC1_ID	  0x07
  #define SHTC1_ID_REG_MASK 0x1f
  
  /* delays for non-blocking i2c commands, both in us */
  #define SHTC1_NONBLOCKING_WAIT_TIME_HPM  14400
  #define SHTC1_NONBLOCKING_WAIT_TIME_LPM   1000
  
  #define SHTC1_CMD_LENGTH      2
  #define SHTC1_RESPONSE_LENGTH 6
  
  struct shtc1_data {
  	struct i2c_client *client;
  	struct mutex update_lock;
  	bool valid;
  	unsigned long last_updated; /* in jiffies */
  
  	const unsigned char *command;
  	unsigned int nonblocking_wait_time; /* in us */
  
  	struct shtc1_platform_data setup;
  
  	int temperature; /* 1000 * temperature in dgr C */
  	int humidity; /* 1000 * relative humidity in %RH */
  };
  
  static int shtc1_update_values(struct i2c_client *client,
  			       struct shtc1_data *data,
  			       char *buf, int bufsize)
  {
  	int ret = i2c_master_send(client, data->command, SHTC1_CMD_LENGTH);
  	if (ret != SHTC1_CMD_LENGTH) {
  		dev_err(&client->dev, "failed to send command: %d
  ", ret);
  		return ret < 0 ? ret : -EIO;
  	}
  
  	/*
  	 * In blocking mode (clock stretching mode) the I2C bus
  	 * is blocked for other traffic, thus the call to i2c_master_recv()
  	 * will wait until the data is ready. For non blocking mode, we
  	 * have to wait ourselves.
  	 */
  	if (!data->setup.blocking_io)
  		usleep_range(data->nonblocking_wait_time,
  			     data->nonblocking_wait_time + 1000);
  
  	ret = i2c_master_recv(client, buf, bufsize);
  	if (ret != bufsize) {
  		dev_err(&client->dev, "failed to read values: %d
  ", ret);
  		return ret < 0 ? ret : -EIO;
  	}
  
  	return 0;
  }
  
  /* sysfs attributes */
  static struct shtc1_data *shtc1_update_client(struct device *dev)
  {
  	struct shtc1_data *data = dev_get_drvdata(dev);
  	struct i2c_client *client = data->client;
  	unsigned char buf[SHTC1_RESPONSE_LENGTH];
  	int val;
  	int ret = 0;
  
  	mutex_lock(&data->update_lock);
  
  	if (time_after(jiffies, data->last_updated + HZ / 10) || !data->valid) {
  		ret = shtc1_update_values(client, data, buf, sizeof(buf));
  		if (ret)
  			goto out;
  
  		/*
  		 * From datasheet:
  		 * T = -45 + 175 * ST / 2^16
  		 * RH = 100 * SRH / 2^16
  		 *
  		 * Adapted for integer fixed point (3 digit) arithmetic.
  		 */
  		val = be16_to_cpup((__be16 *)buf);
  		data->temperature = ((21875 * val) >> 13) - 45000;
  		val = be16_to_cpup((__be16 *)(buf + 3));
  		data->humidity = ((12500 * val) >> 13);
  
  		data->last_updated = jiffies;
  		data->valid = true;
  	}
  
  out:
  	mutex_unlock(&data->update_lock);
  
  	return ret == 0 ? data : ERR_PTR(ret);
  }
  
  static ssize_t temp1_input_show(struct device *dev,
  				struct device_attribute *attr,
  				char *buf)
  {
  	struct shtc1_data *data = shtc1_update_client(dev);
  	if (IS_ERR(data))
  		return PTR_ERR(data);
  
  	return sprintf(buf, "%d
  ", data->temperature);
  }
  
  static ssize_t humidity1_input_show(struct device *dev,
  				    struct device_attribute *attr, char *buf)
  {
  	struct shtc1_data *data = shtc1_update_client(dev);
  	if (IS_ERR(data))
  		return PTR_ERR(data);
  
  	return sprintf(buf, "%d
  ", data->humidity);
  }
  
  static DEVICE_ATTR_RO(temp1_input);
  static DEVICE_ATTR_RO(humidity1_input);
  
  static struct attribute *shtc1_attrs[] = {
  	&dev_attr_temp1_input.attr,
  	&dev_attr_humidity1_input.attr,
  	NULL
  };
  
  ATTRIBUTE_GROUPS(shtc1);
  
  static void shtc1_select_command(struct shtc1_data *data)
  {
  	if (data->setup.high_precision) {
  		data->command = data->setup.blocking_io ?
  				shtc1_cmd_measure_blocking_hpm :
  				shtc1_cmd_measure_nonblocking_hpm;
  		data->nonblocking_wait_time = SHTC1_NONBLOCKING_WAIT_TIME_HPM;
  
  	} else {
  		data->command = data->setup.blocking_io ?
  				shtc1_cmd_measure_blocking_lpm :
  				shtc1_cmd_measure_nonblocking_lpm;
  		data->nonblocking_wait_time = SHTC1_NONBLOCKING_WAIT_TIME_LPM;
  	}
  }
  
  static int shtc1_probe(struct i2c_client *client,
  		       const struct i2c_device_id *id)
  {
  	int ret;
  	char id_reg[2];
  	struct shtc1_data *data;
  	struct device *hwmon_dev;
  	struct i2c_adapter *adap = client->adapter;
  	struct device *dev = &client->dev;
  
  	if (!i2c_check_functionality(adap, I2C_FUNC_I2C)) {
  		dev_err(dev, "plain i2c transactions not supported
  ");
  		return -ENODEV;
  	}
  
  	ret = i2c_master_send(client, shtc1_cmd_read_id_reg, SHTC1_CMD_LENGTH);
  	if (ret != SHTC1_CMD_LENGTH) {
  		dev_err(dev, "could not send read_id_reg command: %d
  ", ret);
  		return ret < 0 ? ret : -ENODEV;
  	}
  	ret = i2c_master_recv(client, id_reg, sizeof(id_reg));
  	if (ret != sizeof(id_reg)) {
  		dev_err(dev, "could not read ID register: %d
  ", ret);
  		return -ENODEV;
  	}
  	if ((id_reg[1] & SHTC1_ID_REG_MASK) != SHTC1_ID) {
  		dev_err(dev, "ID register doesn't match
  ");
  		return -ENODEV;
  	}
  
  	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  
  	data->setup.blocking_io = false;
  	data->setup.high_precision = true;
  	data->client = client;
  
  	if (client->dev.platform_data)
  		data->setup = *(struct shtc1_platform_data *)dev->platform_data;
  	shtc1_select_command(data);
  	mutex_init(&data->update_lock);
  
  	hwmon_dev = devm_hwmon_device_register_with_groups(dev,
  							   client->name,
  							   data,
  							   shtc1_groups);
  	if (IS_ERR(hwmon_dev))
  		dev_dbg(dev, "unable to register hwmon device
  ");
  
  	return PTR_ERR_OR_ZERO(hwmon_dev);
  }
  
  /* device ID table */
  static const struct i2c_device_id shtc1_id[] = {
  	{ "shtc1", 0 },
  	{ "shtw1", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, shtc1_id);
  
  static struct i2c_driver shtc1_i2c_driver = {
  	.driver.name  = "shtc1",
  	.probe        = shtc1_probe,
  	.id_table     = shtc1_id,
  };
  
  module_i2c_driver(shtc1_i2c_driver);
  
  MODULE_AUTHOR("Johannes Winkelmann <johannes.winkelmann@sensirion.com>");
  MODULE_DESCRIPTION("Sensirion SHTC1 humidity and temperature sensor driver");
  MODULE_LICENSE("GPL");