/*
   * sht15.c - support for the SHT15 Temperature and Humidity Sensor
   *

   * Portions Copyright (c) 2010-2011 Savoir-faire Linux Inc.

   *          Jerome Oufella <jerome.oufella@savoirfairelinux.com>

   *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>
   *

   * Copyright (c) 2009 Jonathan Cameron
   *
   * Copyright (c) 2007 Wouter Horre
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *

   * For further information, see the Documentation/hwmon/sht15 file.

   */
  
  #include <linux/interrupt.h>
  #include <linux/irq.h>
  #include <linux/gpio.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/hwmon.h>
  #include <linux/hwmon-sysfs.h>
  #include <linux/mutex.h>
  #include <linux/platform_device.h>

  #include <linux/sched.h>

  #include <linux/delay.h>
  #include <linux/jiffies.h>
  #include <linux/err.h>
  #include <linux/sht15.h>
  #include <linux/regulator/consumer.h>

  #include <linux/slab.h>

  #include <linux/atomic.h>

  /* Commands */
  #define SHT15_MEASURE_TEMP		0x03
  #define SHT15_MEASURE_RH		0x05

  #define SHT15_WRITE_STATUS		0x06
  #define SHT15_READ_STATUS		0x07

  #define SHT15_SOFT_RESET		0x1E

  /* Min timings */
  #define SHT15_TSCKL			100	/* (nsecs) clock low */
  #define SHT15_TSCKH			100	/* (nsecs) clock high */
  #define SHT15_TSU			150	/* (nsecs) data setup time */

  #define SHT15_TSRST			11	/* (msecs) soft reset time */

  /* Status Register Bits */
  #define SHT15_STATUS_LOW_RESOLUTION	0x01
  #define SHT15_STATUS_NO_OTP_RELOAD	0x02
  #define SHT15_STATUS_HEATER		0x04
  #define SHT15_STATUS_LOW_BATTERY	0x40

  /* Actions the driver may be doing */
  enum sht15_state {
  	SHT15_READING_NOTHING,
  	SHT15_READING_TEMP,
  	SHT15_READING_HUMID
  };

  
  /**

   * struct sht15_temppair - elements of voltage dependent temp calc

   * @vdd:	supply voltage in microvolts
   * @d1:		see data sheet
   */
  struct sht15_temppair {
  	int vdd; /* microvolts */
  	int d1;
  };

  /* Table 9 from datasheet - relates temperature calculation to supply voltage */

  static const struct sht15_temppair temppoints[] = {
  	{ 2500000, -39400 },
  	{ 3000000, -39600 },
  	{ 3500000, -39700 },
  	{ 4000000, -39800 },
  	{ 5000000, -40100 },
  };

  /* Table from CRC datasheet, section 2.4 */
  static const u8 sht15_crc8_table[] = {
  	0,	49,	98,	83,	196,	245,	166,	151,
  	185,	136,	219,	234,	125,	76,	31,	46,
  	67,	114,	33,	16,	135,	182,	229,	212,
  	250,	203,	152,	169,	62,	15,	92,	109,
  	134,	183,	228,	213,	66,	115,	32,	17,
  	63,	14,	93,	108,	251,	202,	153,	168,
  	197,	244,	167,	150,	1,	48,	99,	82,
  	124,	77,	30,	47,	184,	137,	218,	235,
  	61,	12,	95,	110,	249,	200,	155,	170,
  	132,	181,	230,	215,	64,	113,	34,	19,
  	126,	79,	28,	45,	186,	139,	216,	233,
  	199,	246,	165,	148,	3,	50,	97,	80,
  	187,	138,	217,	232,	127,	78,	29,	44,
  	2,	51,	96,	81,	198,	247,	164,	149,
  	248,	201,	154,	171,	60,	13,	94,	111,
  	65,	112,	35,	18,	133,	180,	231,	214,
  	122,	75,	24,	41,	190,	143,	220,	237,
  	195,	242,	161,	144,	7,	54,	101,	84,
  	57,	8,	91,	106,	253,	204,	159,	174,
  	128,	177,	226,	211,	68,	117,	38,	23,
  	252,	205,	158,	175,	56,	9,	90,	107,
  	69,	116,	39,	22,	129,	176,	227,	210,
  	191,	142,	221,	236,	123,	74,	25,	40,
  	6,	55,	100,	85,	194,	243,	160,	145,
  	71,	118,	37,	20,	131,	178,	225,	208,
  	254,	207,	156,	173,	58,	11,	88,	105,
  	4,	53,	102,	87,	192,	241,	162,	147,
  	189,	140,	223,	238,	121,	72,	27,	42,
  	193,	240,	163,	146,	5,	52,	103,	86,
  	120,	73,	26,	43,	188,	141,	222,	239,
  	130,	179,	224,	209,	70,	119,	36,	21,
  	59,	10,	89,	104,	255,	206,	157,	172
  };

  /**
   * struct sht15_data - device instance specific data

   * @pdata:		platform data (gpio's etc).
   * @read_work:		bh of interrupt handler.
   * @wait_queue:		wait queue for getting values from device.
   * @val_temp:		last temperature value read from device.
   * @val_humid:		last humidity value read from device.

   * @val_status:		last status register value read from device.

   * @checksum_ok:	last value read from the device passed CRC validation.
   * @checksumming:	flag used to enable the data validation with CRC.

   * @state:		state identifying the action the driver is doing.
   * @measurements_valid:	are the current stored measures valid (start condition).

   * @status_valid:	is the current stored status valid (start condition).

   * @last_measurement:	time of last measure.

   * @last_status:	time of last status reading.

   * @read_lock:		mutex to ensure only one read in progress at a time.
   * @dev:		associate device structure.
   * @hwmon_dev:		device associated with hwmon subsystem.
   * @reg:		associated regulator (if specified).
   * @nb:			notifier block to handle notifications of voltage
   *                      changes.
   * @supply_uV:		local copy of supply voltage used to allow use of
   *                      regulator consumer if available.
   * @supply_uV_valid:	indicates that an updated value has not yet been
   *			obtained from the regulator and so any calculations
   *			based upon it will be invalid.
   * @update_supply_work:	work struct that is used to update the supply_uV.
   * @interrupt_handled:	flag used to indicate a handler has been scheduled.

   */
  struct sht15_data {
  	struct sht15_platform_data	*pdata;
  	struct work_struct		read_work;
  	wait_queue_head_t		wait_queue;
  	uint16_t			val_temp;
  	uint16_t			val_humid;

  	u8				val_status;

  	bool				checksum_ok;
  	bool				checksumming;

  	enum sht15_state		state;
  	bool				measurements_valid;

  	bool				status_valid;

  	unsigned long			last_measurement;

  	unsigned long			last_status;

  	struct mutex			read_lock;
  	struct device			*dev;
  	struct device			*hwmon_dev;
  	struct regulator		*reg;
  	struct notifier_block		nb;
  	int				supply_uV;

  	bool				supply_uV_valid;

  	struct work_struct		update_supply_work;
  	atomic_t			interrupt_handled;
  };
  
  /**

   * sht15_reverse() - reverse a byte
   * @byte:    byte to reverse.
   */
  static u8 sht15_reverse(u8 byte)
  {
  	u8 i, c;
  
  	for (c = 0, i = 0; i < 8; i++)
  		c |= (!!(byte & (1 << i))) << (7 - i);
  	return c;
  }
  
  /**
   * sht15_crc8() - compute crc8
   * @data:	sht15 specific data.
   * @value:	sht15 retrieved data.
   *
   * This implements section 2 of the CRC datasheet.
   */
  static u8 sht15_crc8(struct sht15_data *data,
  		const u8 *value,
  		int len)
  {
  	u8 crc = sht15_reverse(data->val_status & 0x0F);
  
  	while (len--) {
  		crc = sht15_crc8_table[*value ^ crc];
  		value++;
  	}
  
  	return crc;
  }
  
  /**

   * sht15_connection_reset() - reset the comms interface
   * @data:	sht15 specific data
   *
   * This implements section 3.4 of the data sheet
   */
  static void sht15_connection_reset(struct sht15_data *data)
  {
  	int i;

  	gpio_direction_output(data->pdata->gpio_data, 1);
  	ndelay(SHT15_TSCKL);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  	for (i = 0; i < 9; ++i) {
  		gpio_set_value(data->pdata->gpio_sck, 1);
  		ndelay(SHT15_TSCKH);
  		gpio_set_value(data->pdata->gpio_sck, 0);
  		ndelay(SHT15_TSCKL);
  	}
  }

  /**
   * sht15_send_bit() - send an individual bit to the device
   * @data:	device state data
   * @val:	value of bit to be sent

   */

  static inline void sht15_send_bit(struct sht15_data *data, int val)
  {

  	gpio_set_value(data->pdata->gpio_data, val);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSCKH);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL); /* clock low time */
  }
  
  /**
   * sht15_transmission_start() - specific sequence for new transmission

   * @data:	device state data

   *

   * Timings for this are not documented on the data sheet, so very
   * conservative ones used in implementation. This implements
   * figure 12 on the data sheet.

   */

  static void sht15_transmission_start(struct sht15_data *data)
  {
  	/* ensure data is high and output */
  	gpio_direction_output(data->pdata->gpio_data, 1);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSCKH);
  	gpio_set_value(data->pdata->gpio_data, 0);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSCKH);
  	gpio_set_value(data->pdata->gpio_data, 1);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  }

  /**
   * sht15_send_byte() - send a single byte to the device
   * @data:	device state
   * @byte:	value to be sent

   */

  static void sht15_send_byte(struct sht15_data *data, u8 byte)
  {
  	int i;

  	for (i = 0; i < 8; i++) {
  		sht15_send_bit(data, !!(byte & 0x80));
  		byte <<= 1;
  	}
  }

  /**
   * sht15_wait_for_response() - checks for ack from device
   * @data:	device state

   */

  static int sht15_wait_for_response(struct sht15_data *data)
  {
  	gpio_direction_input(data->pdata->gpio_data);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSCKH);
  	if (gpio_get_value(data->pdata->gpio_data)) {
  		gpio_set_value(data->pdata->gpio_sck, 0);
  		dev_err(data->dev, "Command not acknowledged
  ");
  		sht15_connection_reset(data);
  		return -EIO;
  	}
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  	return 0;
  }
  
  /**
   * sht15_send_cmd() - Sends a command to the device.
   * @data:	device state
   * @cmd:	command byte to be sent
   *
   * On entry, sck is output low, data is output pull high
   * and the interrupt disabled.

   */

  static int sht15_send_cmd(struct sht15_data *data, u8 cmd)
  {
  	int ret = 0;

  	sht15_transmission_start(data);
  	sht15_send_byte(data, cmd);
  	ret = sht15_wait_for_response(data);
  	return ret;
  }

  /**

   * sht15_soft_reset() - send a soft reset command
   * @data:	sht15 specific data.
   *
   * As described in section 3.2 of the datasheet.
   */
  static int sht15_soft_reset(struct sht15_data *data)
  {
  	int ret;
  
  	ret = sht15_send_cmd(data, SHT15_SOFT_RESET);
  	if (ret)
  		return ret;
  	msleep(SHT15_TSRST);

  	/* device resets default hardware status register value */
  	data->val_status = 0;
  
  	return ret;
  }
  
  /**

   * sht15_ack() - send a ack
   * @data:	sht15 specific data.
   *
   * Each byte of data is acknowledged by pulling the data line
   * low for one clock pulse.
   */
  static void sht15_ack(struct sht15_data *data)
  {
  	gpio_direction_output(data->pdata->gpio_data, 0);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_data, 1);
  
  	gpio_direction_input(data->pdata->gpio_data);
  }
  
  /**

   * sht15_end_transmission() - notify device of end of transmission
   * @data:	device state.
   *
   * This is basically a NAK (single clock pulse, data high).
   */
  static void sht15_end_transmission(struct sht15_data *data)
  {
  	gpio_direction_output(data->pdata->gpio_data, 1);
  	ndelay(SHT15_TSU);
  	gpio_set_value(data->pdata->gpio_sck, 1);
  	ndelay(SHT15_TSCKH);
  	gpio_set_value(data->pdata->gpio_sck, 0);
  	ndelay(SHT15_TSCKL);
  }
  
  /**
   * sht15_read_byte() - Read a byte back from the device
   * @data:	device state.
   */
  static u8 sht15_read_byte(struct sht15_data *data)
  {
  	int i;
  	u8 byte = 0;
  
  	for (i = 0; i < 8; ++i) {
  		byte <<= 1;
  		gpio_set_value(data->pdata->gpio_sck, 1);
  		ndelay(SHT15_TSCKH);
  		byte |= !!gpio_get_value(data->pdata->gpio_data);
  		gpio_set_value(data->pdata->gpio_sck, 0);
  		ndelay(SHT15_TSCKL);
  	}
  	return byte;
  }
  
  /**
   * sht15_send_status() - write the status register byte
   * @data:	sht15 specific data.
   * @status:	the byte to set the status register with.
   *
   * As described in figure 14 and table 5 of the datasheet.
   */
  static int sht15_send_status(struct sht15_data *data, u8 status)
  {
  	int ret;
  
  	ret = sht15_send_cmd(data, SHT15_WRITE_STATUS);
  	if (ret)
  		return ret;
  	gpio_direction_output(data->pdata->gpio_data, 1);
  	ndelay(SHT15_TSU);
  	sht15_send_byte(data, status);
  	ret = sht15_wait_for_response(data);
  	if (ret)
  		return ret;

  	data->val_status = status;

  	return 0;
  }
  
  /**

   * sht15_update_status() - get updated status register from device if too old
   * @data:	device instance specific data.
   *
   * As described in figure 15 and table 5 of the datasheet.
   */
  static int sht15_update_status(struct sht15_data *data)
  {
  	int ret = 0;
  	u8 status;

  	u8 previous_config;
  	u8 dev_checksum = 0;
  	u8 checksum_vals[2];

  	int timeout = HZ;
  
  	mutex_lock(&data->read_lock);
  	if (time_after(jiffies, data->last_status + timeout)
  			|| !data->status_valid) {
  		ret = sht15_send_cmd(data, SHT15_READ_STATUS);
  		if (ret)
  			goto error_ret;
  		status = sht15_read_byte(data);

  		if (data->checksumming) {
  			sht15_ack(data);
  			dev_checksum = sht15_reverse(sht15_read_byte(data));
  			checksum_vals[0] = SHT15_READ_STATUS;
  			checksum_vals[1] = status;
  			data->checksum_ok = (sht15_crc8(data, checksum_vals, 2)
  					== dev_checksum);
  		}

  		sht15_end_transmission(data);

  		/*
  		 * Perform checksum validation on the received data.
  		 * Specification mentions that in case a checksum verification
  		 * fails, a soft reset command must be sent to the device.
  		 */
  		if (data->checksumming && !data->checksum_ok) {
  			previous_config = data->val_status & 0x07;
  			ret = sht15_soft_reset(data);
  			if (ret)
  				goto error_ret;
  			if (previous_config) {
  				ret = sht15_send_status(data, previous_config);
  				if (ret) {
  					dev_err(data->dev,
  						"CRC validation failed, unable "
  						"to restore device settings
  ");
  					goto error_ret;
  				}
  			}
  			ret = -EAGAIN;
  			goto error_ret;
  		}

  		data->val_status = status;
  		data->status_valid = true;
  		data->last_status = jiffies;
  	}
  error_ret:
  	mutex_unlock(&data->read_lock);
  
  	return ret;
  }
  
  /**

   * sht15_measurement() - get a new value from device

   * @data:		device instance specific data
   * @command:		command sent to request value
   * @timeout_msecs:	timeout after which comms are assumed
   *			to have failed are reset.

   */
  static int sht15_measurement(struct sht15_data *data,
  			     int command,
  			     int timeout_msecs)

  {
  	int ret;

  	u8 previous_config;

  	ret = sht15_send_cmd(data, command);
  	if (ret)
  		return ret;
  
  	gpio_direction_input(data->pdata->gpio_data);
  	atomic_set(&data->interrupt_handled, 0);
  
  	enable_irq(gpio_to_irq(data->pdata->gpio_data));
  	if (gpio_get_value(data->pdata->gpio_data) == 0) {
  		disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));

  		/* Only relevant if the interrupt hasn't occurred. */

  		if (!atomic_read(&data->interrupt_handled))
  			schedule_work(&data->read_work);
  	}
  	ret = wait_event_timeout(data->wait_queue,

  				 (data->state == SHT15_READING_NOTHING),

  				 msecs_to_jiffies(timeout_msecs));
  	if (ret == 0) {/* timeout occurred */

  		disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));

  		sht15_connection_reset(data);
  		return -ETIME;
  	}

  
  	/*
  	 *  Perform checksum validation on the received data.
  	 *  Specification mentions that in case a checksum verification fails,
  	 *  a soft reset command must be sent to the device.
  	 */
  	if (data->checksumming && !data->checksum_ok) {
  		previous_config = data->val_status & 0x07;
  		ret = sht15_soft_reset(data);
  		if (ret)
  			return ret;
  		if (previous_config) {
  			ret = sht15_send_status(data, previous_config);
  			if (ret) {
  				dev_err(data->dev,
  					"CRC validation failed, unable "
  					"to restore device settings
  ");
  				return ret;
  			}
  		}
  		return -EAGAIN;
  	}

  	return 0;
  }
  
  /**

   * sht15_update_measurements() - get updated measures from device if too old

   * @data:	device state

   */
  static int sht15_update_measurements(struct sht15_data *data)

  {
  	int ret = 0;
  	int timeout = HZ;
  
  	mutex_lock(&data->read_lock);

  	if (time_after(jiffies, data->last_measurement + timeout)
  	    || !data->measurements_valid) {
  		data->state = SHT15_READING_HUMID;
  		ret = sht15_measurement(data, SHT15_MEASURE_RH, 160);

  		if (ret)
  			goto error_ret;

  		data->state = SHT15_READING_TEMP;
  		ret = sht15_measurement(data, SHT15_MEASURE_TEMP, 400);

  		if (ret)
  			goto error_ret;

  		data->measurements_valid = true;
  		data->last_measurement = jiffies;

  	}
  error_ret:
  	mutex_unlock(&data->read_lock);
  
  	return ret;
  }
  
  /**
   * sht15_calc_temp() - convert the raw reading to a temperature
   * @data:	device state
   *
   * As per section 4.3 of the data sheet.

   */

  static inline int sht15_calc_temp(struct sht15_data *data)
  {

  	int d1 = temppoints[0].d1;

  	int d2 = (data->val_status & SHT15_STATUS_LOW_RESOLUTION) ? 40 : 10;

  	int i;

  	for (i = ARRAY_SIZE(temppoints) - 1; i > 0; i--)

  		/* Find pointer to interpolate */
  		if (data->supply_uV > temppoints[i - 1].vdd) {

  			d1 = (data->supply_uV - temppoints[i - 1].vdd)

  				* (temppoints[i].d1 - temppoints[i - 1].d1)
  				/ (temppoints[i].vdd - temppoints[i - 1].vdd)
  				+ temppoints[i - 1].d1;
  			break;
  		}

  	return data->val_temp * d2 + d1;

  }
  
  /**
   * sht15_calc_humid() - using last temperature convert raw to humid
   * @data:	device state
   *
   * This is the temperature compensated version as per section 4.2 of
   * the data sheet.

   *
   * The sensor is assumed to be V3, which is compatible with V4.
   * Humidity conversion coefficients are shown in table 7 of the datasheet.
   */

  static inline int sht15_calc_humid(struct sht15_data *data)
  {

  	int rh_linear; /* milli percent */

  	int temp = sht15_calc_temp(data);

  	int c2, c3;
  	int t2;

  	const int c1 = -4;

  
  	if (data->val_status & SHT15_STATUS_LOW_RESOLUTION) {
  		c2 = 648000; /* x 10 ^ -6 */
  		c3 = -7200;  /* x 10 ^ -7 */
  		t2 = 1280;
  	} else {
  		c2 = 40500;  /* x 10 ^ -6 */
  		c3 = -28;    /* x 10 ^ -7 */
  		t2 = 80;
  	}

  	rh_linear = c1 * 1000
  		+ c2 * data->val_humid / 1000

  		+ (data->val_humid * data->val_humid * c3) / 10000;

  	return (temp - 25000) * (10000 + t2 * data->val_humid)

  		/ 1000000 + rh_linear;

  }

  /**

   * sht15_show_status() - show status information in sysfs
   * @dev:	device.
   * @attr:	device attribute.
   * @buf:	sysfs buffer where information is written to.
   *
   * Will be called on read access to temp1_fault, humidity1_fault
   * and heater_enable sysfs attributes.
   * Returns number of bytes written into buffer, negative errno on error.
   */
  static ssize_t sht15_show_status(struct device *dev,
  				 struct device_attribute *attr,
  				 char *buf)
  {
  	int ret;
  	struct sht15_data *data = dev_get_drvdata(dev);
  	u8 bit = to_sensor_dev_attr(attr)->index;
  
  	ret = sht15_update_status(data);
  
  	return ret ? ret : sprintf(buf, "%d
  ", !!(data->val_status & bit));
  }
  
  /**
   * sht15_store_heater() - change heater state via sysfs
   * @dev:	device.
   * @attr:	device attribute.
   * @buf:	sysfs buffer to read the new heater state from.
   * @count:	length of the data.
   *

   * Will be called on write access to heater_enable sysfs attribute.

   * Returns number of bytes actually decoded, negative errno on error.
   */
  static ssize_t sht15_store_heater(struct device *dev,
  				  struct device_attribute *attr,
  				  const char *buf, size_t count)
  {
  	int ret;
  	struct sht15_data *data = dev_get_drvdata(dev);
  	long value;
  	u8 status;

  	if (kstrtol(buf, 10, &value))

  		return -EINVAL;
  
  	mutex_lock(&data->read_lock);
  	status = data->val_status & 0x07;
  	if (!!value)
  		status |= SHT15_STATUS_HEATER;
  	else
  		status &= ~SHT15_STATUS_HEATER;
  
  	ret = sht15_send_status(data, status);
  	mutex_unlock(&data->read_lock);
  
  	return ret ? ret : count;
  }
  
  /**

   * sht15_show_temp() - show temperature measurement value in sysfs
   * @dev:	device.
   * @attr:	device attribute.
   * @buf:	sysfs buffer 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 sht15_show_temp(struct device *dev,
  			       struct device_attribute *attr,
  			       char *buf)
  {
  	int ret;
  	struct sht15_data *data = dev_get_drvdata(dev);
  
  	/* Technically no need to read humidity as well */

  	ret = sht15_update_measurements(data);

  
  	return ret ? ret : sprintf(buf, "%d
  ",
  				   sht15_calc_temp(data));
  }

  /**
   * sht15_show_humidity() - show humidity measurement value in sysfs
   * @dev:	device.
   * @attr:	device attribute.
   * @buf:	sysfs buffer 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 sht15_show_humidity(struct device *dev,
  				   struct device_attribute *attr,
  				   char *buf)
  {
  	int ret;
  	struct sht15_data *data = dev_get_drvdata(dev);

  	ret = sht15_update_measurements(data);

  
  	return ret ? ret : sprintf(buf, "%d
  ", sht15_calc_humid(data));

  }

  static ssize_t show_name(struct device *dev,
  			 struct device_attribute *attr,
  			 char *buf)
  {
  	struct platform_device *pdev = to_platform_device(dev);
  	return sprintf(buf, "%s
  ", pdev->name);
  }

  static SENSOR_DEVICE_ATTR(temp1_input, S_IRUGO,
  			  sht15_show_temp, NULL, 0);
  static SENSOR_DEVICE_ATTR(humidity1_input, S_IRUGO,
  			  sht15_show_humidity, NULL, 0);

  static SENSOR_DEVICE_ATTR(temp1_fault, S_IRUGO, sht15_show_status, NULL,
  			  SHT15_STATUS_LOW_BATTERY);
  static SENSOR_DEVICE_ATTR(humidity1_fault, S_IRUGO, sht15_show_status, NULL,
  			  SHT15_STATUS_LOW_BATTERY);
  static SENSOR_DEVICE_ATTR(heater_enable, S_IRUGO | S_IWUSR, sht15_show_status,
  			  sht15_store_heater, SHT15_STATUS_HEATER);

  static DEVICE_ATTR(name, S_IRUGO, show_name, NULL);
  static struct attribute *sht15_attrs[] = {
  	&sensor_dev_attr_temp1_input.dev_attr.attr,
  	&sensor_dev_attr_humidity1_input.dev_attr.attr,

  	&sensor_dev_attr_temp1_fault.dev_attr.attr,
  	&sensor_dev_attr_humidity1_fault.dev_attr.attr,
  	&sensor_dev_attr_heater_enable.dev_attr.attr,

  	&dev_attr_name.attr,
  	NULL,
  };
  
  static const struct attribute_group sht15_attr_group = {
  	.attrs = sht15_attrs,
  };
  
  static irqreturn_t sht15_interrupt_fired(int irq, void *d)
  {
  	struct sht15_data *data = d;

  	/* First disable the interrupt */
  	disable_irq_nosync(irq);
  	atomic_inc(&data->interrupt_handled);
  	/* Then schedule a reading work struct */

  	if (data->state != SHT15_READING_NOTHING)

  		schedule_work(&data->read_work);
  	return IRQ_HANDLED;
  }

  static void sht15_bh_read_data(struct work_struct *work_s)
  {

  	uint16_t val = 0;

  	u8 dev_checksum = 0;
  	u8 checksum_vals[3];

  	struct sht15_data *data
  		= container_of(work_s, struct sht15_data,
  			       read_work);

  	/* Firstly, verify the line is low */
  	if (gpio_get_value(data->pdata->gpio_data)) {

  		/*
  		 * If not, then start the interrupt again - care here as could
  		 * have gone low in meantime so verify it hasn't!
  		 */

  		atomic_set(&data->interrupt_handled, 0);
  		enable_irq(gpio_to_irq(data->pdata->gpio_data));

  		/* If still not occurred or another handler has been scheduled */

  		if (gpio_get_value(data->pdata->gpio_data)
  		    || atomic_read(&data->interrupt_handled))
  			return;
  	}

  	/* Read the data back from the device */

  	val = sht15_read_byte(data);
  	val <<= 8;
  	sht15_ack(data);
  	val |= sht15_read_byte(data);

  	if (data->checksumming) {
  		/*
  		 * Ask the device for a checksum and read it back.
  		 * Note: the device sends the checksum byte reversed.
  		 */
  		sht15_ack(data);
  		dev_checksum = sht15_reverse(sht15_read_byte(data));
  		checksum_vals[0] = (data->state == SHT15_READING_TEMP) ?
  			SHT15_MEASURE_TEMP : SHT15_MEASURE_RH;
  		checksum_vals[1] = (u8) (val >> 8);
  		checksum_vals[2] = (u8) val;
  		data->checksum_ok
  			= (sht15_crc8(data, checksum_vals, 3) == dev_checksum);
  	}

  	/* Tell the device we are done */
  	sht15_end_transmission(data);

  	switch (data->state) {

  	case SHT15_READING_TEMP:
  		data->val_temp = val;
  		break;
  	case SHT15_READING_HUMID:
  		data->val_humid = val;
  		break;

  	default:
  		break;

  	}

  	data->state = SHT15_READING_NOTHING;

  	wake_up(&data->wait_queue);
  }
  
  static void sht15_update_voltage(struct work_struct *work_s)
  {
  	struct sht15_data *data
  		= container_of(work_s, struct sht15_data,
  			       update_supply_work);
  	data->supply_uV = regulator_get_voltage(data->reg);
  }
  
  /**
   * sht15_invalidate_voltage() - mark supply voltage invalid when notified by reg
   * @nb:		associated notification structure
   * @event:	voltage regulator state change event code
   * @ignored:	function parameter - ignored here
   *
   * Note that as the notification code holds the regulator lock, we have
   * to schedule an update of the supply voltage rather than getting it directly.

   */

  static int sht15_invalidate_voltage(struct notifier_block *nb,

  				    unsigned long event,
  				    void *ignored)

  {
  	struct sht15_data *data = container_of(nb, struct sht15_data, nb);
  
  	if (event == REGULATOR_EVENT_VOLTAGE_CHANGE)
  		data->supply_uV_valid = false;
  	schedule_work(&data->update_supply_work);
  
  	return NOTIFY_OK;
  }
  
  static int __devinit sht15_probe(struct platform_device *pdev)
  {
  	int ret = 0;
  	struct sht15_data *data = kzalloc(sizeof(*data), GFP_KERNEL);

  	u8 status = 0;

  
  	if (!data) {
  		ret = -ENOMEM;

  		dev_err(&pdev->dev, "kzalloc failed
  ");

  		goto error_ret;
  	}
  
  	INIT_WORK(&data->read_work, sht15_bh_read_data);
  	INIT_WORK(&data->update_supply_work, sht15_update_voltage);
  	platform_set_drvdata(pdev, data);
  	mutex_init(&data->read_lock);
  	data->dev = &pdev->dev;
  	init_waitqueue_head(&data->wait_queue);
  
  	if (pdev->dev.platform_data == NULL) {

  		dev_err(&pdev->dev, "no platform data supplied
  ");

  		goto err_free_data;
  	}
  	data->pdata = pdev->dev.platform_data;

  	data->supply_uV = data->pdata->supply_mv * 1000;

  	if (data->pdata->checksum)
  		data->checksumming = true;

  	if (data->pdata->no_otp_reload)
  		status |= SHT15_STATUS_NO_OTP_RELOAD;
  	if (data->pdata->low_resolution)
  		status |= SHT15_STATUS_LOW_RESOLUTION;

  	/*
  	 * If a regulator is available,
  	 * query what the supply voltage actually is!
  	 */

  	data->reg = regulator_get(data->dev, "vcc");
  	if (!IS_ERR(data->reg)) {

  		int voltage;
  
  		voltage = regulator_get_voltage(data->reg);
  		if (voltage)
  			data->supply_uV = voltage;

  		regulator_enable(data->reg);

  		/*
  		 * Setup a notifier block to update this if another device
  		 * causes the voltage to change
  		 */

  		data->nb.notifier_call = &sht15_invalidate_voltage;
  		ret = regulator_register_notifier(data->reg, &data->nb);

  		if (ret) {
  			dev_err(&pdev->dev,
  				"regulator notifier request failed
  ");
  			regulator_disable(data->reg);
  			regulator_put(data->reg);
  			goto err_free_data;
  		}

  	}

  
  	/* Try requesting the GPIOs */

  	ret = gpio_request(data->pdata->gpio_sck, "SHT15 sck");
  	if (ret) {

  		dev_err(&pdev->dev, "gpio request failed
  ");

  		goto err_release_reg;

  	}
  	gpio_direction_output(data->pdata->gpio_sck, 0);

  	ret = gpio_request(data->pdata->gpio_data, "SHT15 data");
  	if (ret) {

  		dev_err(&pdev->dev, "gpio request failed
  ");

  		goto err_release_gpio_sck;
  	}

  
  	ret = request_irq(gpio_to_irq(data->pdata->gpio_data),
  			  sht15_interrupt_fired,
  			  IRQF_TRIGGER_FALLING,
  			  "sht15 data",
  			  data);
  	if (ret) {

  		dev_err(&pdev->dev, "failed to get irq for data line
  ");

  		goto err_release_gpio_data;
  	}
  	disable_irq_nosync(gpio_to_irq(data->pdata->gpio_data));
  	sht15_connection_reset(data);

  	ret = sht15_soft_reset(data);
  	if (ret)
  		goto err_release_irq;

  	/* write status with platform data options */
  	if (status) {
  		ret = sht15_send_status(data, status);
  		if (ret)
  			goto err_release_irq;
  	}

  	ret = sysfs_create_group(&pdev->dev.kobj, &sht15_attr_group);
  	if (ret) {
  		dev_err(&pdev->dev, "sysfs create failed
  ");
  		goto err_release_irq;
  	}

  
  	data->hwmon_dev = hwmon_device_register(data->dev);
  	if (IS_ERR(data->hwmon_dev)) {
  		ret = PTR_ERR(data->hwmon_dev);

  		goto err_release_sysfs_group;

  	}

  	return 0;

  err_release_sysfs_group:
  	sysfs_remove_group(&pdev->dev.kobj, &sht15_attr_group);

  err_release_irq:
  	free_irq(gpio_to_irq(data->pdata->gpio_data), data);

  err_release_gpio_data:
  	gpio_free(data->pdata->gpio_data);
  err_release_gpio_sck:
  	gpio_free(data->pdata->gpio_sck);

  err_release_reg:
  	if (!IS_ERR(data->reg)) {
  		regulator_unregister_notifier(data->reg, &data->nb);
  		regulator_disable(data->reg);
  		regulator_put(data->reg);
  	}

  err_free_data:
  	kfree(data);
  error_ret:

  	return ret;
  }
  
  static int __devexit sht15_remove(struct platform_device *pdev)
  {
  	struct sht15_data *data = platform_get_drvdata(pdev);

  	/*
  	 * Make sure any reads from the device are done and
  	 * prevent new ones beginning
  	 */

  	mutex_lock(&data->read_lock);

  	if (sht15_soft_reset(data)) {
  		mutex_unlock(&data->read_lock);
  		return -EFAULT;
  	}

  	hwmon_device_unregister(data->hwmon_dev);
  	sysfs_remove_group(&pdev->dev.kobj, &sht15_attr_group);
  	if (!IS_ERR(data->reg)) {
  		regulator_unregister_notifier(data->reg, &data->nb);
  		regulator_disable(data->reg);
  		regulator_put(data->reg);
  	}
  
  	free_irq(gpio_to_irq(data->pdata->gpio_data), data);
  	gpio_free(data->pdata->gpio_data);
  	gpio_free(data->pdata->gpio_sck);
  	mutex_unlock(&data->read_lock);
  	kfree(data);

  	return 0;
  }

  /*
   * sht_drivers simultaneously refers to __devinit and __devexit function
   * which causes spurious section mismatch warning. So use __refdata to
   * get rid from this.
   */
  static struct platform_driver __refdata sht_drivers[] = {

  	{
  		.driver = {
  			.name = "sht10",
  			.owner = THIS_MODULE,
  		},
  		.probe = sht15_probe,

  		.remove = __devexit_p(sht15_remove),

  	}, {
  		.driver = {
  			.name = "sht11",
  			.owner = THIS_MODULE,
  		},
  		.probe = sht15_probe,

  		.remove = __devexit_p(sht15_remove),

  	}, {
  		.driver = {
  			.name = "sht15",
  			.owner = THIS_MODULE,
  		},
  		.probe = sht15_probe,

  		.remove = __devexit_p(sht15_remove),

  	}, {
  		.driver = {
  			.name = "sht71",
  			.owner = THIS_MODULE,
  		},
  		.probe = sht15_probe,

  		.remove = __devexit_p(sht15_remove),

  	}, {
  		.driver = {
  			.name = "sht75",
  			.owner = THIS_MODULE,
  		},
  		.probe = sht15_probe,

  		.remove = __devexit_p(sht15_remove),

  	},
  };

  static int __init sht15_init(void)
  {
  	int ret;
  	int i;
  
  	for (i = 0; i < ARRAY_SIZE(sht_drivers); i++) {
  		ret = platform_driver_register(&sht_drivers[i]);
  		if (ret)
  			goto error_unreg;
  	}
  
  	return 0;
  
  error_unreg:
  	while (--i >= 0)
  		platform_driver_unregister(&sht_drivers[i]);
  
  	return ret;
  }
  module_init(sht15_init);
  
  static void __exit sht15_exit(void)
  {
  	int i;
  	for (i = ARRAY_SIZE(sht_drivers) - 1; i >= 0; i--)
  		platform_driver_unregister(&sht_drivers[i]);
  }
  module_exit(sht15_exit);
  
  MODULE_LICENSE("GPL");