drivers/iio/proximity/srf04.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * SRF04: ultrasonic sensor for distance measuring by using GPIOs
  *
  * Copyright (c) 2017 Andreas Klinger <ak@it-klinger.de>
  *
  * For details about the device see:
  * https://www.robot-electronics.co.uk/htm/srf04tech.htm
  *
  * the measurement cycle as timing diagram looks like:
  *
  *          +---+
  * GPIO     |   |
  * trig:  --+   +------------------------------------------------------
  *          ^   ^
  *          |<->|
  *         udelay(trigger_pulse_us)
  *
  * ultra           +-+ +-+ +-+
  * sonic           | | | | | |
  * burst: ---------+ +-+ +-+ +-----------------------------------------
  *                           .
  * ultra                     .              +-+ +-+ +-+
  * sonic                     .              | | | | | |
  * echo:  ----------------------------------+ +-+ +-+ +----------------
  *                           .                        .
  *                           +------------------------+
  * GPIO                      |                        |
  * echo:  -------------------+                        +---------------
  *                           ^                        ^
  *                           interrupt                interrupt
  *                           (ts_rising)              (ts_falling)
  *                           |<---------------------->|
  *                              pulse time measured
  *                              --> one round trip of ultra sonic waves
  */
 #include <linux/err.h>
 #include <linux/gpio/consumer.h>
 #include <linux/kernel.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
 #include <linux/sched.h>
 #include <linux/interrupt.h>
 #include <linux/delay.h>
 #include <linux/pm_runtime.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>

 struct srf04_cfg {
 	unsigned long trigger_pulse_us;
 };

 struct srf04_data {
 	struct device		*dev;
 	struct gpio_desc	*gpiod_trig;
 	struct gpio_desc	*gpiod_echo;
 	struct gpio_desc	*gpiod_power;
 	struct mutex		lock;
 	int			irqnr;
 	ktime_t			ts_rising;
 	ktime_t			ts_falling;
 	struct completion	rising;
 	struct completion	falling;
 	const struct srf04_cfg	*cfg;
 	int			startup_time_ms;
 };

 static const struct srf04_cfg srf04_cfg = {
 	.trigger_pulse_us = 10,
 };

 static const struct srf04_cfg mb_lv_cfg = {
 	.trigger_pulse_us = 20,
 };

 static irqreturn_t srf04_handle_irq(int irq, void *dev_id)
 {
 	struct iio_dev *indio_dev = dev_id;
 	struct srf04_data *data = iio_priv(indio_dev);
 	ktime_t now = ktime_get();

 	if (gpiod_get_value(data->gpiod_echo)) {
 		data->ts_rising = now;
 		complete(&data->rising);
 	} else {
 		data->ts_falling = now;
 		complete(&data->falling);
 	}

 	return IRQ_HANDLED;
 }

 static int srf04_read(struct srf04_data *data)
 {
 	int ret;
 	ktime_t ktime_dt;
 	u64 dt_ns;
 	u32 time_ns, distance_mm;

 	if (data->gpiod_power) {
 		ret = pm_runtime_resume_and_get(data->dev);
 		if (ret < 0)
 			return ret;
 	}
 	/*
 	 * just one read-echo-cycle can take place at a time
 	 * ==> lock against concurrent reading calls
 	 */
 	mutex_lock(&data->lock);

 	reinit_completion(&data->rising);
 	reinit_completion(&data->falling);

 	gpiod_set_value(data->gpiod_trig, 1);
 	udelay(data->cfg->trigger_pulse_us);
 	gpiod_set_value(data->gpiod_trig, 0);

 	if (data->gpiod_power) {
 		pm_runtime_mark_last_busy(data->dev);
 		pm_runtime_put_autosuspend(data->dev);
 	}

 	/* it should not take more than 20 ms until echo is rising */
 	ret = wait_for_completion_killable_timeout(&data->rising, HZ/50);
 	if (ret < 0) {
 		mutex_unlock(&data->lock);
 		return ret;
 	} else if (ret == 0) {
 		mutex_unlock(&data->lock);
 		return -ETIMEDOUT;
 	}

 	/* it cannot take more than 50 ms until echo is falling */
 	ret = wait_for_completion_killable_timeout(&data->falling, HZ/20);
 	if (ret < 0) {
 		mutex_unlock(&data->lock);
 		return ret;
 	} else if (ret == 0) {
 		mutex_unlock(&data->lock);
 		return -ETIMEDOUT;
 	}

 	ktime_dt = ktime_sub(data->ts_falling, data->ts_rising);

 	mutex_unlock(&data->lock);

 	dt_ns = ktime_to_ns(ktime_dt);
 	/*
 	 * measuring more than 6,45 meters is beyond the capabilities of
 	 * the supported sensors
 	 * ==> filter out invalid results for not measuring echos of
 	 *     another us sensor
 	 *
 	 * formula:
 	 *         distance     6,45 * 2 m
 	 * time = ---------- = ------------ = 40438871 ns
 	 *          speed         319 m/s
 	 *
 	 * using a minimum speed at -20 °C of 319 m/s
 	 */
 	if (dt_ns > 40438871)
 		return -EIO;

 	time_ns = dt_ns;

 	/*
 	 * the speed as function of the temperature is approximately:
 	 *
 	 * speed = 331,5 + 0,6 * Temp
 	 *   with Temp in °C
 	 *   and speed in m/s
 	 *
 	 * use 343,5 m/s as ultrasonic speed at 20 °C here in absence of the
 	 * temperature
 	 *
 	 * therefore:
 	 *             time     343,5     time * 106
 	 * distance = ------ * ------- = ------------
 	 *             10^6         2         617176
 	 *   with time in ns
 	 *   and distance in mm (one way)
 	 *
 	 * because we limit to 6,45 meters the multiplication with 106 just
 	 * fits into 32 bit
 	 */
 	distance_mm = time_ns * 106 / 617176;

 	return distance_mm;
 }

 static int srf04_read_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *channel, int *val,
 			    int *val2, long info)
 {
 	struct srf04_data *data = iio_priv(indio_dev);
 	int ret;

 	if (channel->type != IIO_DISTANCE)
 		return -EINVAL;

 	switch (info) {
 	case IIO_CHAN_INFO_RAW:
 		ret = srf04_read(data);
 		if (ret < 0)
 			return ret;
 		*val = ret;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		/*
 		 * theoretical maximum resolution is 3 mm
 		 * 1 LSB is 1 mm
 		 */
 		*val = 0;
 		*val2 = 1000;
 		return IIO_VAL_INT_PLUS_MICRO;
 	default:
 		return -EINVAL;
 	}
 }

 static const struct iio_info srf04_iio_info = {
 	.read_raw		= srf04_read_raw,
 };

 static const struct iio_chan_spec srf04_chan_spec[] = {
 	{
 		.type = IIO_DISTANCE,
 		.info_mask_separate =
 				BIT(IIO_CHAN_INFO_RAW) |
 				BIT(IIO_CHAN_INFO_SCALE),
 	},
 };

 static const struct of_device_id of_srf04_match[] = {
 	{ .compatible = "devantech,srf04", .data = &srf04_cfg },
 	{ .compatible = "maxbotix,mb1000", .data = &mb_lv_cfg },
 	{ .compatible = "maxbotix,mb1010", .data = &mb_lv_cfg },
 	{ .compatible = "maxbotix,mb1020", .data = &mb_lv_cfg },
 	{ .compatible = "maxbotix,mb1030", .data = &mb_lv_cfg },
 	{ .compatible = "maxbotix,mb1040", .data = &mb_lv_cfg },
 	{},
 };

 MODULE_DEVICE_TABLE(of, of_srf04_match);

 static int srf04_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct srf04_data *data;
 	struct iio_dev *indio_dev;
 	int ret;

 	indio_dev = devm_iio_device_alloc(dev, sizeof(struct srf04_data));
 	if (!indio_dev) {
 		dev_err(dev, "failed to allocate IIO device\n");
 		return -ENOMEM;
 	}

 	data = iio_priv(indio_dev);
 	data->dev = dev;
 	data->cfg = device_get_match_data(dev);

 	mutex_init(&data->lock);
 	init_completion(&data->rising);
 	init_completion(&data->falling);

 	data->gpiod_trig = devm_gpiod_get(dev, "trig", GPIOD_OUT_LOW);
 	if (IS_ERR(data->gpiod_trig)) {
 		dev_err(dev, "failed to get trig-gpios: err=%ld\n",
 					PTR_ERR(data->gpiod_trig));
 		return PTR_ERR(data->gpiod_trig);
 	}

 	data->gpiod_echo = devm_gpiod_get(dev, "echo", GPIOD_IN);
 	if (IS_ERR(data->gpiod_echo)) {
 		dev_err(dev, "failed to get echo-gpios: err=%ld\n",
 					PTR_ERR(data->gpiod_echo));
 		return PTR_ERR(data->gpiod_echo);
 	}

 	data->gpiod_power = devm_gpiod_get_optional(dev, "power",
 								GPIOD_OUT_LOW);
 	if (IS_ERR(data->gpiod_power)) {
 		dev_err(dev, "failed to get power-gpios: err=%ld\n",
 						PTR_ERR(data->gpiod_power));
 		return PTR_ERR(data->gpiod_power);
 	}
 	if (data->gpiod_power) {
 		data->startup_time_ms = 100;
 		device_property_read_u32(dev, "startup-time-ms", &data->startup_time_ms);
 		dev_dbg(dev, "using power gpio: startup-time-ms=%d\n",
 							data->startup_time_ms);
 	}

 	if (gpiod_cansleep(data->gpiod_echo)) {
 		dev_err(data->dev, "cansleep-GPIOs not supported\n");
 		return -ENODEV;
 	}

 	data->irqnr = gpiod_to_irq(data->gpiod_echo);
 	if (data->irqnr < 0) {
 		dev_err(data->dev, "gpiod_to_irq: %d\n", data->irqnr);
 		return data->irqnr;
 	}

 	ret = devm_request_irq(dev, data->irqnr, srf04_handle_irq,
 			IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
 			pdev->name, indio_dev);
 	if (ret < 0) {
 		dev_err(data->dev, "request_irq: %d\n", ret);
 		return ret;
 	}

 	platform_set_drvdata(pdev, indio_dev);

 	indio_dev->name = "srf04";
 	indio_dev->info = &srf04_iio_info;
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->channels = srf04_chan_spec;
 	indio_dev->num_channels = ARRAY_SIZE(srf04_chan_spec);

 	ret = iio_device_register(indio_dev);
 	if (ret < 0) {
 		dev_err(data->dev, "iio_device_register: %d\n", ret);
 		return ret;
 	}

 	if (data->gpiod_power) {
 		pm_runtime_set_autosuspend_delay(data->dev, 1000);
 		pm_runtime_use_autosuspend(data->dev);

 		ret = pm_runtime_set_active(data->dev);
 		if (ret) {
 			dev_err(data->dev, "pm_runtime_set_active: %d\n", ret);
 			iio_device_unregister(indio_dev);
 		}

 		pm_runtime_enable(data->dev);
 		pm_runtime_idle(data->dev);
 	}

 	return ret;
 }

 static int srf04_remove(struct platform_device *pdev)
 {
 	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
 	struct srf04_data *data = iio_priv(indio_dev);

 	iio_device_unregister(indio_dev);

 	if (data->gpiod_power) {
 		pm_runtime_disable(data->dev);
 		pm_runtime_set_suspended(data->dev);
 	}

 	return 0;
 }

 static int  srf04_pm_runtime_suspend(struct device *dev)
 {
 	struct platform_device *pdev = container_of(dev,
 						struct platform_device, dev);
 	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
 	struct srf04_data *data = iio_priv(indio_dev);

 	gpiod_set_value(data->gpiod_power, 0);

 	return 0;
 }

 static int srf04_pm_runtime_resume(struct device *dev)
 {
 	struct platform_device *pdev = container_of(dev,
 						struct platform_device, dev);
 	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
 	struct srf04_data *data = iio_priv(indio_dev);

 	gpiod_set_value(data->gpiod_power, 1);
 	msleep(data->startup_time_ms);

 	return 0;
 }

 static const struct dev_pm_ops srf04_pm_ops = {
 	RUNTIME_PM_OPS(srf04_pm_runtime_suspend,
 		       srf04_pm_runtime_resume, NULL)
 };

 static struct platform_driver srf04_driver = {
 	.probe		= srf04_probe,
 	.remove		= srf04_remove,
 	.driver		= {
 		.name		= "srf04-gpio",
 		.of_match_table	= of_srf04_match,
 		.pm		= pm_ptr(&srf04_pm_ops),
 	},
 };

 module_platform_driver(srf04_driver);

 MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
 MODULE_DESCRIPTION("SRF04 ultrasonic sensor for distance measuring using GPIOs");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("platform:srf04");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* SRF04: ultrasonic sensor for distance measuring by using GPIOs
	*
	* Copyright (c) 2017 Andreas Klinger <ak@it-klinger.de>
	*
	* For details about the device see:
	* https://www.robot-electronics.co.uk/htm/srf04tech.htm
	*
	* the measurement cycle as timing diagram looks like:
	*
	* +---+
	* GPIO \| \|
	* trig: --+ +------------------------------------------------------
	* ^ ^
	* \|<->\|
	* udelay(trigger_pulse_us)
	*
	* ultra +-+ +-+ +-+
	* sonic \| \| \| \| \| \|
	* burst: ---------+ +-+ +-+ +-----------------------------------------
	* .
	* ultra . +-+ +-+ +-+
	* sonic . \| \| \| \| \| \|
	* echo: ----------------------------------+ +-+ +-+ +----------------
	* . .
	* +------------------------+
	* GPIO \| \|
	* echo: -------------------+ +---------------
	* ^ ^
	* interrupt interrupt
	* (ts_rising) (ts_falling)
	* \|<---------------------->\|
	* pulse time measured
	* --> one round trip of ultra sonic waves
	*/
	#include <linux/err.h>
	#include <linux/gpio/consumer.h>
	#include <linux/kernel.h>
	#include <linux/mod_devicetable.h>
	#include <linux/module.h>
	#include <linux/platform_device.h>
	#include <linux/property.h>
	#include <linux/sched.h>
	#include <linux/interrupt.h>
	#include <linux/delay.h>
	#include <linux/pm_runtime.h>
	#include <linux/iio/iio.h>
	#include <linux/iio/sysfs.h>

	struct srf04_cfg {
	unsigned long trigger_pulse_us;
	};

	struct srf04_data {
	struct device *dev;
	struct gpio_desc *gpiod_trig;
	struct gpio_desc *gpiod_echo;
	struct gpio_desc *gpiod_power;
	struct mutex lock;
	int irqnr;
	ktime_t ts_rising;
	ktime_t ts_falling;
	struct completion rising;
	struct completion falling;
	const struct srf04_cfg *cfg;
	int startup_time_ms;
	};

	static const struct srf04_cfg srf04_cfg = {
	.trigger_pulse_us = 10,
	};

	static const struct srf04_cfg mb_lv_cfg = {
	.trigger_pulse_us = 20,
	};

	static irqreturn_t srf04_handle_irq(int irq, void *dev_id)
	{
	struct iio_dev *indio_dev = dev_id;
	struct srf04_data *data = iio_priv(indio_dev);
	ktime_t now = ktime_get();

	if (gpiod_get_value(data->gpiod_echo)) {
	data->ts_rising = now;
	complete(&data->rising);
	} else {
	data->ts_falling = now;
	complete(&data->falling);
	}

	return IRQ_HANDLED;
	}

	static int srf04_read(struct srf04_data *data)
	{
	int ret;
	ktime_t ktime_dt;
	u64 dt_ns;
	u32 time_ns, distance_mm;

	if (data->gpiod_power) {
	ret = pm_runtime_resume_and_get(data->dev);
	if (ret < 0)
	return ret;
	}
	/*
	* just one read-echo-cycle can take place at a time
	* ==> lock against concurrent reading calls
	*/
	mutex_lock(&data->lock);

	reinit_completion(&data->rising);
	reinit_completion(&data->falling);

	gpiod_set_value(data->gpiod_trig, 1);
	udelay(data->cfg->trigger_pulse_us);
	gpiod_set_value(data->gpiod_trig, 0);

	if (data->gpiod_power) {
	pm_runtime_mark_last_busy(data->dev);
	pm_runtime_put_autosuspend(data->dev);
	}

	/* it should not take more than 20 ms until echo is rising */
	ret = wait_for_completion_killable_timeout(&data->rising, HZ/50);
	if (ret < 0) {
	mutex_unlock(&data->lock);
	return ret;
	} else if (ret == 0) {
	mutex_unlock(&data->lock);
	return -ETIMEDOUT;
	}

	/* it cannot take more than 50 ms until echo is falling */
	ret = wait_for_completion_killable_timeout(&data->falling, HZ/20);
	if (ret < 0) {
	mutex_unlock(&data->lock);
	return ret;
	} else if (ret == 0) {
	mutex_unlock(&data->lock);
	return -ETIMEDOUT;
	}

	ktime_dt = ktime_sub(data->ts_falling, data->ts_rising);

	mutex_unlock(&data->lock);

	dt_ns = ktime_to_ns(ktime_dt);
	/*
	* measuring more than 6,45 meters is beyond the capabilities of
	* the supported sensors
	* ==> filter out invalid results for not measuring echos of
	* another us sensor
	*
	* formula:
	* distance 6,45 * 2 m
	* time = ---------- = ------------ = 40438871 ns
	* speed 319 m/s
	*
	* using a minimum speed at -20 °C of 319 m/s
	*/
	if (dt_ns > 40438871)
	return -EIO;

	time_ns = dt_ns;

	/*
	* the speed as function of the temperature is approximately:
	*
	* speed = 331,5 + 0,6 * Temp
	* with Temp in °C
	* and speed in m/s
	*
	* use 343,5 m/s as ultrasonic speed at 20 °C here in absence of the
	* temperature
	*
	* therefore:
	* time 343,5 time * 106
	* distance = ------ * ------- = ------------
	* 10^6 2 617176
	* with time in ns
	* and distance in mm (one way)
	*
	* because we limit to 6,45 meters the multiplication with 106 just
	* fits into 32 bit
	*/
	distance_mm = time_ns * 106 / 617176;

	return distance_mm;
	}

	static int srf04_read_raw(struct iio_dev *indio_dev,
	struct iio_chan_spec const channel, int val,
	int *val2, long info)
	{
	struct srf04_data *data = iio_priv(indio_dev);
	int ret;

	if (channel->type != IIO_DISTANCE)
	return -EINVAL;

	switch (info) {
	case IIO_CHAN_INFO_RAW:
	ret = srf04_read(data);
	if (ret < 0)
	return ret;
	*val = ret;
	return IIO_VAL_INT;
	case IIO_CHAN_INFO_SCALE:
	/*
	* theoretical maximum resolution is 3 mm
	* 1 LSB is 1 mm
	*/
	*val = 0;
	*val2 = 1000;
	return IIO_VAL_INT_PLUS_MICRO;
	default:
	return -EINVAL;
	}
	}

	static const struct iio_info srf04_iio_info = {
	.read_raw = srf04_read_raw,
	};

	static const struct iio_chan_spec srf04_chan_spec[] = {
	{
	.type = IIO_DISTANCE,
	.info_mask_separate =
	BIT(IIO_CHAN_INFO_RAW) \|
	BIT(IIO_CHAN_INFO_SCALE),
	},
	};

	static const struct of_device_id of_srf04_match[] = {
	{ .compatible = "devantech,srf04", .data = &srf04_cfg },
	{ .compatible = "maxbotix,mb1000", .data = &mb_lv_cfg },
	{ .compatible = "maxbotix,mb1010", .data = &mb_lv_cfg },
	{ .compatible = "maxbotix,mb1020", .data = &mb_lv_cfg },
	{ .compatible = "maxbotix,mb1030", .data = &mb_lv_cfg },
	{ .compatible = "maxbotix,mb1040", .data = &mb_lv_cfg },
	{},
	};

	MODULE_DEVICE_TABLE(of, of_srf04_match);

	static int srf04_probe(struct platform_device *pdev)
	{
	struct device *dev = &pdev->dev;
	struct srf04_data *data;
	struct iio_dev *indio_dev;
	int ret;

	indio_dev = devm_iio_device_alloc(dev, sizeof(struct srf04_data));
	if (!indio_dev) {
	dev_err(dev, "failed to allocate IIO device\n");
	return -ENOMEM;
	}

	data = iio_priv(indio_dev);
	data->dev = dev;
	data->cfg = device_get_match_data(dev);

	mutex_init(&data->lock);
	init_completion(&data->rising);
	init_completion(&data->falling);

	data->gpiod_trig = devm_gpiod_get(dev, "trig", GPIOD_OUT_LOW);
	if (IS_ERR(data->gpiod_trig)) {
	dev_err(dev, "failed to get trig-gpios: err=%ld\n",
	PTR_ERR(data->gpiod_trig));
	return PTR_ERR(data->gpiod_trig);
	}

	data->gpiod_echo = devm_gpiod_get(dev, "echo", GPIOD_IN);
	if (IS_ERR(data->gpiod_echo)) {
	dev_err(dev, "failed to get echo-gpios: err=%ld\n",
	PTR_ERR(data->gpiod_echo));
	return PTR_ERR(data->gpiod_echo);
	}

	data->gpiod_power = devm_gpiod_get_optional(dev, "power",
	GPIOD_OUT_LOW);
	if (IS_ERR(data->gpiod_power)) {
	dev_err(dev, "failed to get power-gpios: err=%ld\n",
	PTR_ERR(data->gpiod_power));
	return PTR_ERR(data->gpiod_power);
	}
	if (data->gpiod_power) {
	data->startup_time_ms = 100;
	device_property_read_u32(dev, "startup-time-ms", &data->startup_time_ms);
	dev_dbg(dev, "using power gpio: startup-time-ms=%d\n",
	data->startup_time_ms);
	}

	if (gpiod_cansleep(data->gpiod_echo)) {
	dev_err(data->dev, "cansleep-GPIOs not supported\n");
	return -ENODEV;
	}

	data->irqnr = gpiod_to_irq(data->gpiod_echo);
	if (data->irqnr < 0) {
	dev_err(data->dev, "gpiod_to_irq: %d\n", data->irqnr);
	return data->irqnr;
	}

	ret = devm_request_irq(dev, data->irqnr, srf04_handle_irq,
	IRQF_TRIGGER_RISING \| IRQF_TRIGGER_FALLING,
	pdev->name, indio_dev);
	if (ret < 0) {
	dev_err(data->dev, "request_irq: %d\n", ret);
	return ret;
	}

	platform_set_drvdata(pdev, indio_dev);

	indio_dev->name = "srf04";
	indio_dev->info = &srf04_iio_info;
	indio_dev->modes = INDIO_DIRECT_MODE;
	indio_dev->channels = srf04_chan_spec;
	indio_dev->num_channels = ARRAY_SIZE(srf04_chan_spec);

	ret = iio_device_register(indio_dev);
	if (ret < 0) {
	dev_err(data->dev, "iio_device_register: %d\n", ret);
	return ret;
	}

	if (data->gpiod_power) {
	pm_runtime_set_autosuspend_delay(data->dev, 1000);
	pm_runtime_use_autosuspend(data->dev);

	ret = pm_runtime_set_active(data->dev);
	if (ret) {
	dev_err(data->dev, "pm_runtime_set_active: %d\n", ret);
	iio_device_unregister(indio_dev);
	}

	pm_runtime_enable(data->dev);
	pm_runtime_idle(data->dev);
	}

	return ret;
	}

	static int srf04_remove(struct platform_device *pdev)
	{
	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
	struct srf04_data *data = iio_priv(indio_dev);

	iio_device_unregister(indio_dev);

	if (data->gpiod_power) {
	pm_runtime_disable(data->dev);
	pm_runtime_set_suspended(data->dev);
	}

	return 0;
	}

	static int srf04_pm_runtime_suspend(struct device *dev)
	{
	struct platform_device *pdev = container_of(dev,
	struct platform_device, dev);
	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
	struct srf04_data *data = iio_priv(indio_dev);

	gpiod_set_value(data->gpiod_power, 0);

	return 0;
	}

	static int srf04_pm_runtime_resume(struct device *dev)
	{
	struct platform_device *pdev = container_of(dev,
	struct platform_device, dev);
	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
	struct srf04_data *data = iio_priv(indio_dev);

	gpiod_set_value(data->gpiod_power, 1);
	msleep(data->startup_time_ms);

	return 0;
	}

	static const struct dev_pm_ops srf04_pm_ops = {
	RUNTIME_PM_OPS(srf04_pm_runtime_suspend,
	srf04_pm_runtime_resume, NULL)
	};

	static struct platform_driver srf04_driver = {
	.probe = srf04_probe,
	.remove = srf04_remove,
	.driver = {
	.name = "srf04-gpio",
	.of_match_table = of_srf04_match,
	.pm = pm_ptr(&srf04_pm_ops),
	},
	};

	module_platform_driver(srf04_driver);

	MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
	MODULE_DESCRIPTION("SRF04 ultrasonic sensor for distance measuring using GPIOs");
	MODULE_LICENSE("GPL");
	MODULE_ALIAS("platform:srf04");