drivers/iio/humidity/dht11.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * DHT11/DHT22 bit banging GPIO driver
  *
  * Copyright (c) Harald Geyer <harald@ccbib.org>
  */

 #include <linux/err.h>
 #include <linux/interrupt.h>
 #include <linux/device.h>
 #include <linux/kernel.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/sysfs.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/wait.h>
 #include <linux/bitops.h>
 #include <linux/completion.h>
 #include <linux/mutex.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>
 #include <linux/timekeeping.h>

 #include <linux/iio/iio.h>

 #define DRIVER_NAME	"dht11"

 #define DHT11_DATA_VALID_TIME	2000000000  /* 2s in ns */

 #define DHT11_EDGES_PREAMBLE 2
 #define DHT11_BITS_PER_READ 40
 /*
  * Note that when reading the sensor actually 84 edges are detected, but
  * since the last edge is not significant, we only store 83:
  */
 #define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
 			      DHT11_EDGES_PREAMBLE + 1)

 /*
  * Data transmission timing:
  * Data bits are encoded as pulse length (high time) on the data line.
  * 0-bit: 22-30uS -- typically 26uS (AM2302)
  * 1-bit: 68-75uS -- typically 70uS (AM2302)
  * The acutal timings also depend on the properties of the cable, with
  * longer cables typically making pulses shorter.
  *
  * Our decoding depends on the time resolution of the system:
  * timeres > 34uS ... don't know what a 1-tick pulse is
  * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
  * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
  * timeres < 23uS ... no problem
  *
  * Luckily clocks in the 33-44kHz range are quite uncommon, so we can
  * support most systems if the threshold for decoding a pulse as 1-bit
  * is chosen carefully. If somebody really wants to support clocks around
  * 40kHz, where this driver is most unreliable, there are two options.
  * a) select an implementation using busy loop polling on those systems
  * b) use the checksum to do some probabilistic decoding
  */
 #define DHT11_START_TRANSMISSION_MIN	18000  /* us */
 #define DHT11_START_TRANSMISSION_MAX	20000  /* us */
 #define DHT11_MIN_TIMERES	34000  /* ns */
 #define DHT11_THRESHOLD		49000  /* ns */
 #define DHT11_AMBIG_LOW		23000  /* ns */
 #define DHT11_AMBIG_HIGH	30000  /* ns */

 struct dht11 {
 	struct device			*dev;

 	struct gpio_desc		*gpiod;
 	int				irq;

 	struct completion		completion;
 	/* The iio sysfs interface doesn't prevent concurrent reads: */
 	struct mutex			lock;

 	s64				timestamp;
 	int				temperature;
 	int				humidity;

 	/* num_edges: -1 means "no transmission in progress" */
 	int				num_edges;
 	struct {s64 ts; int value; }	edges[DHT11_EDGES_PER_READ];
 };

 #ifdef CONFIG_DYNAMIC_DEBUG
 /*
  * dht11_edges_print: show the data as actually received by the
  *                    driver.
  */
 static void dht11_edges_print(struct dht11 *dht11)
 {
 	int i;

 	dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
 	for (i = 1; i < dht11->num_edges; ++i) {
 		dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
 			dht11->edges[i].ts - dht11->edges[i - 1].ts,
 			dht11->edges[i - 1].value ? "high" : "low");
 	}
 }
 #endif /* CONFIG_DYNAMIC_DEBUG */

 static unsigned char dht11_decode_byte(char *bits)
 {
 	unsigned char ret = 0;
 	int i;

 	for (i = 0; i < 8; ++i) {
 		ret <<= 1;
 		if (bits[i])
 			++ret;
 	}

 	return ret;
 }

 static int dht11_decode(struct dht11 *dht11, int offset)
 {
 	int i, t;
 	char bits[DHT11_BITS_PER_READ];
 	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;

 	for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 		t = dht11->edges[offset + 2 * i + 2].ts -
 			dht11->edges[offset + 2 * i + 1].ts;
 		if (!dht11->edges[offset + 2 * i + 1].value) {
 			dev_dbg(dht11->dev,
 				"lost synchronisation at edge %d\n",
 				offset + 2 * i + 1);
 			return -EIO;
 		}
 		bits[i] = t > DHT11_THRESHOLD;
 	}

 	hum_int = dht11_decode_byte(bits);
 	hum_dec = dht11_decode_byte(&bits[8]);
 	temp_int = dht11_decode_byte(&bits[16]);
 	temp_dec = dht11_decode_byte(&bits[24]);
 	checksum = dht11_decode_byte(&bits[32]);

 	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
 		dev_dbg(dht11->dev, "invalid checksum\n");
 		return -EIO;
 	}

 	dht11->timestamp = ktime_get_boottime_ns();
 	if (hum_int < 4) {  /* DHT22: 100000 = (3*256+232)*100 */
 		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
 					((temp_int & 0x80) ? -100 : 100);
 		dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
 	} else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
 		dht11->temperature = temp_int * 1000;
 		dht11->humidity = hum_int * 1000;
 	} else {
 		dev_err(dht11->dev,
 			"Don't know how to decode data: %d %d %d %d\n",
 			hum_int, hum_dec, temp_int, temp_dec);
 		return -EIO;
 	}

 	return 0;
 }

 /*
  * IRQ handler called on GPIO edges
  */
 static irqreturn_t dht11_handle_irq(int irq, void *data)
 {
 	struct iio_dev *iio = data;
 	struct dht11 *dht11 = iio_priv(iio);

 	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
 		dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
 		dht11->edges[dht11->num_edges++].value =
 						gpiod_get_value(dht11->gpiod);

 		if (dht11->num_edges >= DHT11_EDGES_PER_READ)
 			complete(&dht11->completion);
 	}

 	return IRQ_HANDLED;
 }

 static int dht11_read_raw(struct iio_dev *iio_dev,
 			  const struct iio_chan_spec *chan,
 			int *val, int *val2, long m)
 {
 	struct dht11 *dht11 = iio_priv(iio_dev);
 	int ret, timeres, offset;

 	mutex_lock(&dht11->lock);
 	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
 		timeres = ktime_get_resolution_ns();
 		dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
 		if (timeres > DHT11_MIN_TIMERES) {
 			dev_err(dht11->dev, "timeresolution %dns too low\n",
 				timeres);
 			/* In theory a better clock could become available
 			 * at some point ... and there is no error code
 			 * that really fits better.
 			 */
 			ret = -EAGAIN;
 			goto err;
 		}
 		if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
 			dev_warn(dht11->dev,
 				 "timeresolution: %dns - decoding ambiguous\n",
 				 timeres);

 		reinit_completion(&dht11->completion);

 		dht11->num_edges = 0;
 		ret = gpiod_direction_output(dht11->gpiod, 0);
 		if (ret)
 			goto err;
 		usleep_range(DHT11_START_TRANSMISSION_MIN,
 			     DHT11_START_TRANSMISSION_MAX);
 		ret = gpiod_direction_input(dht11->gpiod);
 		if (ret)
 			goto err;

 		ret = request_irq(dht11->irq, dht11_handle_irq,
 				  IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 				  iio_dev->name, iio_dev);
 		if (ret)
 			goto err;

 		ret = wait_for_completion_killable_timeout(&dht11->completion,
 							   HZ);

 		free_irq(dht11->irq, iio_dev);

 #ifdef CONFIG_DYNAMIC_DEBUG
 		dht11_edges_print(dht11);
 #endif

 		if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
 			dev_err(dht11->dev, "Only %d signal edges detected\n",
 				dht11->num_edges);
 			ret = -ETIMEDOUT;
 		}
 		if (ret < 0)
 			goto err;

 		offset = DHT11_EDGES_PREAMBLE +
 				dht11->num_edges - DHT11_EDGES_PER_READ;
 		for (; offset >= 0; --offset) {
 			ret = dht11_decode(dht11, offset);
 			if (!ret)
 				break;
 		}

 		if (ret)
 			goto err;
 	}

 	ret = IIO_VAL_INT;
 	if (chan->type == IIO_TEMP)
 		*val = dht11->temperature;
 	else if (chan->type == IIO_HUMIDITYRELATIVE)
 		*val = dht11->humidity;
 	else
 		ret = -EINVAL;
 err:
 	dht11->num_edges = -1;
 	mutex_unlock(&dht11->lock);
 	return ret;
 }

 static const struct iio_info dht11_iio_info = {
 	.read_raw		= dht11_read_raw,
 };

 static const struct iio_chan_spec dht11_chan_spec[] = {
 	{ .type = IIO_TEMP,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
 	{ .type = IIO_HUMIDITYRELATIVE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
 };

 static const struct of_device_id dht11_dt_ids[] = {
 	{ .compatible = "dht11", },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, dht11_dt_ids);

 static int dht11_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct dht11 *dht11;
 	struct iio_dev *iio;

 	iio = devm_iio_device_alloc(dev, sizeof(*dht11));
 	if (!iio) {
 		dev_err(dev, "Failed to allocate IIO device\n");
 		return -ENOMEM;
 	}

 	dht11 = iio_priv(iio);
 	dht11->dev = dev;
 	dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
 	if (IS_ERR(dht11->gpiod))
 		return PTR_ERR(dht11->gpiod);

 	dht11->irq = gpiod_to_irq(dht11->gpiod);
 	if (dht11->irq < 0) {
 		dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
 		return -EINVAL;
 	}

 	dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
 	dht11->num_edges = -1;

 	platform_set_drvdata(pdev, iio);

 	init_completion(&dht11->completion);
 	mutex_init(&dht11->lock);
 	iio->name = pdev->name;
 	iio->info = &dht11_iio_info;
 	iio->modes = INDIO_DIRECT_MODE;
 	iio->channels = dht11_chan_spec;
 	iio->num_channels = ARRAY_SIZE(dht11_chan_spec);

 	return devm_iio_device_register(dev, iio);
 }

 static struct platform_driver dht11_driver = {
 	.driver = {
 		.name	= DRIVER_NAME,
 		.of_match_table = dht11_dt_ids,
 	},
 	.probe  = dht11_probe,
 };

 module_platform_driver(dht11_driver);

 MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
 MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* DHT11/DHT22 bit banging GPIO driver
	*
	* Copyright (c) Harald Geyer <harald@ccbib.org>
	*/

	#include <linux/err.h>
	#include <linux/interrupt.h>
	#include <linux/device.h>
	#include <linux/kernel.h>
	#include <linux/printk.h>
	#include <linux/slab.h>
	#include <linux/of.h>
	#include <linux/of_device.h>
	#include <linux/sysfs.h>
	#include <linux/io.h>
	#include <linux/module.h>
	#include <linux/platform_device.h>
	#include <linux/wait.h>
	#include <linux/bitops.h>
	#include <linux/completion.h>
	#include <linux/mutex.h>
	#include <linux/delay.h>
	#include <linux/gpio/consumer.h>
	#include <linux/timekeeping.h>

	#include <linux/iio/iio.h>

	#define DRIVER_NAME "dht11"

	#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */

	#define DHT11_EDGES_PREAMBLE 2
	#define DHT11_BITS_PER_READ 40
	/*
	* Note that when reading the sensor actually 84 edges are detected, but
	* since the last edge is not significant, we only store 83:
	*/
	#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
	DHT11_EDGES_PREAMBLE + 1)

	/*
	* Data transmission timing:
	* Data bits are encoded as pulse length (high time) on the data line.
	* 0-bit: 22-30uS -- typically 26uS (AM2302)
	* 1-bit: 68-75uS -- typically 70uS (AM2302)
	* The acutal timings also depend on the properties of the cable, with
	* longer cables typically making pulses shorter.
	*
	* Our decoding depends on the time resolution of the system:
	* timeres > 34uS ... don't know what a 1-tick pulse is
	* 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
	* 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
	* timeres < 23uS ... no problem
	*
	* Luckily clocks in the 33-44kHz range are quite uncommon, so we can
	* support most systems if the threshold for decoding a pulse as 1-bit
	* is chosen carefully. If somebody really wants to support clocks around
	* 40kHz, where this driver is most unreliable, there are two options.
	* a) select an implementation using busy loop polling on those systems
	* b) use the checksum to do some probabilistic decoding
	*/
	#define DHT11_START_TRANSMISSION_MIN 18000 /* us */
	#define DHT11_START_TRANSMISSION_MAX 20000 /* us */
	#define DHT11_MIN_TIMERES 34000 /* ns */
	#define DHT11_THRESHOLD 49000 /* ns */
	#define DHT11_AMBIG_LOW 23000 /* ns */
	#define DHT11_AMBIG_HIGH 30000 /* ns */

	struct dht11 {
	struct device *dev;

	struct gpio_desc *gpiod;
	int irq;

	struct completion completion;
	/* The iio sysfs interface doesn't prevent concurrent reads: */
	struct mutex lock;

	s64 timestamp;
	int temperature;
	int humidity;

	/* num_edges: -1 means "no transmission in progress" */
	int num_edges;
	struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
	};

	#ifdef CONFIG_DYNAMIC_DEBUG
	/*
	* dht11_edges_print: show the data as actually received by the
	* driver.
	*/
	static void dht11_edges_print(struct dht11 *dht11)
	{
	int i;

	dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
	for (i = 1; i < dht11->num_edges; ++i) {
	dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
	dht11->edges[i].ts - dht11->edges[i - 1].ts,
	dht11->edges[i - 1].value ? "high" : "low");
	}
	}
	#endif /* CONFIG_DYNAMIC_DEBUG */

	static unsigned char dht11_decode_byte(char *bits)
	{
	unsigned char ret = 0;
	int i;

	for (i = 0; i < 8; ++i) {
	ret <<= 1;
	if (bits[i])
	++ret;
	}

	return ret;
	}

	static int dht11_decode(struct dht11 *dht11, int offset)
	{
	int i, t;
	char bits[DHT11_BITS_PER_READ];
	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;

	for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
	t = dht11->edges[offset + 2 * i + 2].ts -
	dht11->edges[offset + 2 * i + 1].ts;
	if (!dht11->edges[offset + 2 * i + 1].value) {
	dev_dbg(dht11->dev,
	"lost synchronisation at edge %d\n",
	offset + 2 * i + 1);
	return -EIO;
	}
	bits[i] = t > DHT11_THRESHOLD;
	}

	hum_int = dht11_decode_byte(bits);
	hum_dec = dht11_decode_byte(&bits[8]);
	temp_int = dht11_decode_byte(&bits[16]);
	temp_dec = dht11_decode_byte(&bits[24]);
	checksum = dht11_decode_byte(&bits[32]);

	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
	dev_dbg(dht11->dev, "invalid checksum\n");
	return -EIO;
	}

	dht11->timestamp = ktime_get_boottime_ns();
	if (hum_int < 4) { /* DHT22: 100000 = (3256+232)100 */
	dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
	((temp_int & 0x80) ? -100 : 100);
	dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
	} else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */
	dht11->temperature = temp_int * 1000;
	dht11->humidity = hum_int * 1000;
	} else {
	dev_err(dht11->dev,
	"Don't know how to decode data: %d %d %d %d\n",
	hum_int, hum_dec, temp_int, temp_dec);
	return -EIO;
	}

	return 0;
	}

	/*
	* IRQ handler called on GPIO edges
	*/
	static irqreturn_t dht11_handle_irq(int irq, void *data)
	{
	struct iio_dev *iio = data;
	struct dht11 *dht11 = iio_priv(iio);

	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
	dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
	dht11->edges[dht11->num_edges++].value =
	gpiod_get_value(dht11->gpiod);

	if (dht11->num_edges >= DHT11_EDGES_PER_READ)
	complete(&dht11->completion);
	}

	return IRQ_HANDLED;
	}

	static int dht11_read_raw(struct iio_dev *iio_dev,
	const struct iio_chan_spec *chan,
	int val, int val2, long m)
	{
	struct dht11 *dht11 = iio_priv(iio_dev);
	int ret, timeres, offset;

	mutex_lock(&dht11->lock);
	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
	timeres = ktime_get_resolution_ns();
	dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
	if (timeres > DHT11_MIN_TIMERES) {
	dev_err(dht11->dev, "timeresolution %dns too low\n",
	timeres);
	/* In theory a better clock could become available
	* at some point ... and there is no error code
	* that really fits better.
	*/
	ret = -EAGAIN;
	goto err;
	}
	if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
	dev_warn(dht11->dev,
	"timeresolution: %dns - decoding ambiguous\n",
	timeres);

	reinit_completion(&dht11->completion);

	dht11->num_edges = 0;
	ret = gpiod_direction_output(dht11->gpiod, 0);
	if (ret)
	goto err;
	usleep_range(DHT11_START_TRANSMISSION_MIN,
	DHT11_START_TRANSMISSION_MAX);
	ret = gpiod_direction_input(dht11->gpiod);
	if (ret)
	goto err;

	ret = request_irq(dht11->irq, dht11_handle_irq,
	IRQF_TRIGGER_RISING \| IRQF_TRIGGER_FALLING,
	iio_dev->name, iio_dev);
	if (ret)
	goto err;

	ret = wait_for_completion_killable_timeout(&dht11->completion,
	HZ);

	free_irq(dht11->irq, iio_dev);

	#ifdef CONFIG_DYNAMIC_DEBUG
	dht11_edges_print(dht11);
	#endif

	if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
	dev_err(dht11->dev, "Only %d signal edges detected\n",
	dht11->num_edges);
	ret = -ETIMEDOUT;
	}
	if (ret < 0)
	goto err;

	offset = DHT11_EDGES_PREAMBLE +
	dht11->num_edges - DHT11_EDGES_PER_READ;
	for (; offset >= 0; --offset) {
	ret = dht11_decode(dht11, offset);
	if (!ret)
	break;
	}

	if (ret)
	goto err;
	}

	ret = IIO_VAL_INT;
	if (chan->type == IIO_TEMP)
	*val = dht11->temperature;
	else if (chan->type == IIO_HUMIDITYRELATIVE)
	*val = dht11->humidity;
	else
	ret = -EINVAL;
	err:
	dht11->num_edges = -1;
	mutex_unlock(&dht11->lock);
	return ret;
	}

	static const struct iio_info dht11_iio_info = {
	.read_raw = dht11_read_raw,
	};

	static const struct iio_chan_spec dht11_chan_spec[] = {
	{ .type = IIO_TEMP,
	.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
	{ .type = IIO_HUMIDITYRELATIVE,
	.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
	};

	static const struct of_device_id dht11_dt_ids[] = {
	{ .compatible = "dht11", },
	{ }
	};
	MODULE_DEVICE_TABLE(of, dht11_dt_ids);

	static int dht11_probe(struct platform_device *pdev)
	{
	struct device *dev = &pdev->dev;
	struct dht11 *dht11;
	struct iio_dev *iio;

	iio = devm_iio_device_alloc(dev, sizeof(*dht11));
	if (!iio) {
	dev_err(dev, "Failed to allocate IIO device\n");
	return -ENOMEM;
	}

	dht11 = iio_priv(iio);
	dht11->dev = dev;
	dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
	if (IS_ERR(dht11->gpiod))
	return PTR_ERR(dht11->gpiod);

	dht11->irq = gpiod_to_irq(dht11->gpiod);
	if (dht11->irq < 0) {
	dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
	return -EINVAL;
	}

	dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
	dht11->num_edges = -1;

	platform_set_drvdata(pdev, iio);

	init_completion(&dht11->completion);
	mutex_init(&dht11->lock);
	iio->name = pdev->name;
	iio->info = &dht11_iio_info;
	iio->modes = INDIO_DIRECT_MODE;
	iio->channels = dht11_chan_spec;
	iio->num_channels = ARRAY_SIZE(dht11_chan_spec);

	return devm_iio_device_register(dev, iio);
	}

	static struct platform_driver dht11_driver = {
	.driver = {
	.name = DRIVER_NAME,
	.of_match_table = dht11_dt_ids,
	},
	.probe = dht11_probe,
	};

	module_platform_driver(dht11_driver);

	MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
	MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
	MODULE_LICENSE("GPL v2");