Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1076 insertions, 0 deletions

diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c
new file mode 100644
index 000000000..2be77752c
--- /dev/null
+++ b/drivers/hwmon/sht15.c
@@ -0,0 +1,1076 @@
+/*
+ * sht15.c - support for the SHT15 Temperature and Humidity Sensor
+ *
+ * Portions Copyright (c) 2010-2012 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/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/regulator/consumer.h>
+#include <linux/slab.h>
+#include <linux/atomic.h>
+#include <linux/bitrev.h>
+#include <linux/gpio/consumer.h>
+#include <linux/of.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
+
+/* List of supported chips */
+enum sht15_chips { sht10, sht11, sht15, sht71, sht75 };
+
+/* 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
+ * @sck:		clock GPIO line
+ * @data:		data GPIO line
+ * @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 gpio_desc		*sck;
+	struct gpio_desc		*data;
+	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_crc8() - compute crc8
+ * @data:	sht15 specific data.
+ * @value:	sht15 retrieved data.
+ * @len:	Length of 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 = bitrev8(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 int sht15_connection_reset(struct sht15_data *data)
+{
+	int i, err;
+
+	err = gpiod_direction_output(data->data, 1);
+	if (err)
+		return err;
+	ndelay(SHT15_TSCKL);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSCKL);
+	for (i = 0; i < 9; ++i) {
+		gpiod_set_value(data->sck, 1);
+		ndelay(SHT15_TSCKH);
+		gpiod_set_value(data->sck, 0);
+		ndelay(SHT15_TSCKL);
+	}
+	return 0;
+}
+
+/**
+ * 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)
+{
+	gpiod_set_value(data->data, val);
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSCKH);
+	gpiod_set_value(data->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 int sht15_transmission_start(struct sht15_data *data)
+{
+	int err;
+
+	/* ensure data is high and output */
+	err = gpiod_direction_output(data->data, 1);
+	if (err)
+		return err;
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSCKL);
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSCKH);
+	gpiod_set_value(data->data, 0);
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSCKL);
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSCKH);
+	gpiod_set_value(data->data, 1);
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSCKL);
+	return 0;
+}
+
+/**
+ * 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)
+{
+	int err;
+
+	err = gpiod_direction_input(data->data);
+	if (err)
+		return err;
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSCKH);
+	if (gpiod_get_value(data->data)) {
+		gpiod_set_value(data->sck, 0);
+		dev_err(data->dev, "Command not acknowledged\n");
+		err = sht15_connection_reset(data);
+		if (err)
+			return err;
+		return -EIO;
+	}
+	gpiod_set_value(data->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 err;
+
+	err = sht15_transmission_start(data);
+	if (err)
+		return err;
+	sht15_send_byte(data, cmd);
+	return sht15_wait_for_response(data);
+}
+
+/**
+ * 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 int sht15_ack(struct sht15_data *data)
+{
+	int err;
+
+	err = gpiod_direction_output(data->data, 0);
+	if (err)
+		return err;
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->data, 1);
+
+	return gpiod_direction_input(data->data);
+}
+
+/**
+ * sht15_end_transmission() - notify device of end of transmission
+ * @data:	device state.
+ *
+ * This is basically a NAK (single clock pulse, data high).
+ */
+static int sht15_end_transmission(struct sht15_data *data)
+{
+	int err;
+
+	err = gpiod_direction_output(data->data, 1);
+	if (err)
+		return err;
+	ndelay(SHT15_TSU);
+	gpiod_set_value(data->sck, 1);
+	ndelay(SHT15_TSCKH);
+	gpiod_set_value(data->sck, 0);
+	ndelay(SHT15_TSCKL);
+	return 0;
+}
+
+/**
+ * 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;
+		gpiod_set_value(data->sck, 1);
+		ndelay(SHT15_TSCKH);
+		byte |= !!gpiod_get_value(data->data);
+		gpiod_set_value(data->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 err;
+
+	err = sht15_send_cmd(data, SHT15_WRITE_STATUS);
+	if (err)
+		return err;
+	err = gpiod_direction_output(data->data, 1);
+	if (err)
+		return err;
+	ndelay(SHT15_TSU);
+	sht15_send_byte(data, status);
+	err = sht15_wait_for_response(data);
+	if (err)
+		return err;
+
+	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 unlock;
+		status = sht15_read_byte(data);
+
+		if (data->checksumming) {
+			sht15_ack(data);
+			dev_checksum = bitrev8(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);
+		}
+
+		ret = sht15_end_transmission(data);
+		if (ret)
+			goto unlock;
+
+		/*
+		 * 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 unlock;
+			if (previous_config) {
+				ret = sht15_send_status(data, previous_config);
+				if (ret) {
+					dev_err(data->dev,
+						"CRC validation failed, unable "
+						"to restore device settings\n");
+					goto unlock;
+				}
+			}
+			ret = -EAGAIN;
+			goto unlock;
+		}
+
+		data->val_status = status;
+		data->status_valid = true;
+		data->last_status = jiffies;
+	}
+
+unlock:
+	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;
+
+	ret = gpiod_direction_input(data->data);
+	if (ret)
+		return ret;
+	atomic_set(&data->interrupt_handled, 0);
+
+	enable_irq(gpiod_to_irq(data->data));
+	if (gpiod_get_value(data->data) == 0) {
+		disable_irq_nosync(gpiod_to_irq(data->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 (data->state != SHT15_READING_NOTHING) { /* I/O error occurred */
+		data->state = SHT15_READING_NOTHING;
+		return -EIO;
+	} else if (ret == 0) { /* timeout occurred */
+		disable_irq_nosync(gpiod_to_irq(data->data));
+		ret = sht15_connection_reset(data);
+		if (ret)
+			return ret;
+		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\n");
+				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 unlock;
+		data->state = SHT15_READING_TEMP;
+		ret = sht15_measurement(data, SHT15_MEASURE_TEMP, 400);
+		if (ret)
+			goto unlock;
+		data->measurements_valid = true;
+		data->last_measurement = jiffies;
+	}
+
+unlock:
+	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\n", !!(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\n",
+				   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\n", sht15_calc_humid(data));
+}
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr,
+			 char *buf)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	return sprintf(buf, "%s\n", 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_RO(name);
+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 (gpiod_get_value(data->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(gpiod_to_irq(data->data));
+		/* If still not occurred or another handler was scheduled */
+		if (gpiod_get_value(data->data)
+		    || atomic_read(&data->interrupt_handled))
+			return;
+	}
+
+	/* Read the data back from the device */
+	val = sht15_read_byte(data);
+	val <<= 8;
+	if (sht15_ack(data))
+		goto wakeup;
+	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.
+		 */
+		if (sht15_ack(data))
+			goto wakeup;
+		dev_checksum = bitrev8(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 */
+	if (sht15_end_transmission(data))
+		goto wakeup;
+
+	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;
+wakeup:
+	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;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id sht15_dt_match[] = {
+	{ .compatible = "sensirion,sht15" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, sht15_dt_match);
+#endif
+
+static int sht15_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct sht15_data *data;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	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 a regulator is available,
+	 * query what the supply voltage actually is!
+	 */
+	data->reg = devm_regulator_get_optional(data->dev, "vcc");
+	if (!IS_ERR(data->reg)) {
+		int voltage;
+
+		voltage = regulator_get_voltage(data->reg);
+		if (voltage)
+			data->supply_uv = voltage;
+
+		ret = regulator_enable(data->reg);
+		if (ret != 0) {
+			dev_err(&pdev->dev,
+				"failed to enable regulator: %d\n", ret);
+			return ret;
+		}
+
+		/*
+		 * 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\n");
+			regulator_disable(data->reg);
+			return ret;
+		}
+	}
+
+	/* Try requesting the GPIOs */
+	data->sck = devm_gpiod_get(&pdev->dev, "clk", GPIOD_OUT_LOW);
+	if (IS_ERR(data->sck)) {
+		ret = PTR_ERR(data->sck);
+		dev_err(&pdev->dev, "clock line GPIO request failed\n");
+		goto err_release_reg;
+	}
+	data->data = devm_gpiod_get(&pdev->dev, "data", GPIOD_IN);
+	if (IS_ERR(data->data)) {
+		ret = PTR_ERR(data->data);
+		dev_err(&pdev->dev, "data line GPIO request failed\n");
+		goto err_release_reg;
+	}
+
+	ret = devm_request_irq(&pdev->dev, gpiod_to_irq(data->data),
+			       sht15_interrupt_fired,
+			       IRQF_TRIGGER_FALLING,
+			       "sht15 data",
+			       data);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to get irq for data line\n");
+		goto err_release_reg;
+	}
+	disable_irq_nosync(gpiod_to_irq(data->data));
+	ret = sht15_connection_reset(data);
+	if (ret)
+		goto err_release_reg;
+	ret = sht15_soft_reset(data);
+	if (ret)
+		goto err_release_reg;
+
+	ret = sysfs_create_group(&pdev->dev.kobj, &sht15_attr_group);
+	if (ret) {
+		dev_err(&pdev->dev, "sysfs create failed\n");
+		goto err_release_reg;
+	}
+
+	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_reg:
+	if (!IS_ERR(data->reg)) {
+		regulator_unregister_notifier(data->reg, &data->nb);
+		regulator_disable(data->reg);
+	}
+	return ret;
+}
+
+static int 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);
+	}
+
+	mutex_unlock(&data->read_lock);
+
+	return 0;
+}
+
+static const struct platform_device_id sht15_device_ids[] = {
+	{ "sht10", sht10 },
+	{ "sht11", sht11 },
+	{ "sht15", sht15 },
+	{ "sht71", sht71 },
+	{ "sht75", sht75 },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, sht15_device_ids);
+
+static struct platform_driver sht15_driver = {
+	.driver = {
+		.name = "sht15",
+		.of_match_table = of_match_ptr(sht15_dt_match),
+	},
+	.probe = sht15_probe,
+	.remove = sht15_remove,
+	.id_table = sht15_device_ids,
+};
+module_platform_driver(sht15_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Sensirion SHT15 temperature and humidity sensor driver");