iio: distance: add devantech us ranger srf04

This patch adds support for the ultrasonic ranger srf04 of devantech.

This device is measuring the distance of objects in a range between 1 cm
and 3 meters and a theoretical resolution of 3 mm.

There are two GPIOs used:
  - trigger: set as output to the device when the measurement should start
  - echo: set by the device when the ultrasonic wave is sent out and reset
    when the echo is recognized; this needs to be an interrupt input

The time between setting and resetting the echo pin is the time the
waveform needed for one round trip. This time is recorded in the interrupt
handler.

The distance is calculated in the read function by using the ultrasonic
speed at 20 degrees celsius which is about 343 m/s.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

MAINTAINERS

@@ -3790,6 +3790,12 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git
 S:	Maintained
 F:	drivers/usb/dwc3/
 
+DEVANTECH SRF ULTRASONIC RANGER IIO DRIVER
+M:	Andreas Klinger <ak@it-klinger.de>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	drivers/iio/proximity/srf*.c
+
 DEVICE COREDUMP (DEV_COREDUMP)
 M:	Johannes Berg <johannes@sipsolutions.net>
 L:	linux-kernel@vger.kernel.org

drivers/iio/proximity/Kconfig

@@ -32,6 +32,17 @@ config LIDAR_LITE_V2
 	  To compile this driver as a module, choose M here: the
 	  module will be called pulsedlight-lite-v2
 
+config SRF04
+	tristate "Devantech SRF04 ultrasonic ranger sensor"
+	depends on GPIOLIB
+	help
+	  Say Y here to build a driver for Devantech SRF04 ultrasonic
+	  ranger sensor. This driver can be used to measure the distance
+	  of objects. It is using two GPIOs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called srf04.
+
 config SX9500
 	tristate "SX9500 Semtech proximity sensor"
 	select IIO_BUFFER

drivers/iio/proximity/Makefile

@@ -5,5 +5,6 @@
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AS3935)		+= as3935.o
 obj-$(CONFIG_LIDAR_LITE_V2)	+= pulsedlight-lidar-lite-v2.o
+obj-$(CONFIG_SRF04)		+= srf04.o
 obj-$(CONFIG_SRF08)		+= srf08.o
 obj-$(CONFIG_SX9500)		+= sx9500.o

drivers/iio/proximity/srf04.c

@@ -0,0 +1,304 @@
+/*
+ * SRF04: ultrasonic sensor for distance measuring by using GPIOs
+ *
+ * Copyright (c) 2017 Andreas Klinger <ak@it-klinger.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * For details about the device see:
+ * http://www.robot-electronics.co.uk/htm/srf04tech.htm
+ *
+ * the measurement cycle as timing diagram looks like:
+ *
+ *          +---+
+ * GPIO     |   |
+ * trig:  --+   +------------------------------------------------------
+ *          ^   ^
+ *          |<->|
+ *         udelay(10)
+ *
+ * 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/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/sched.h>
+#include <linux/interrupt.h>
+#include <linux/delay.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+
+struct srf04_data {
+	struct device		*dev;
+	struct gpio_desc	*gpiod_trig;
+	struct gpio_desc	*gpiod_echo;
+	struct mutex		lock;
+	int			irqnr;
+	ktime_t			ts_rising;
+	ktime_t			ts_falling;
+	struct completion	rising;
+	struct completion	falling;
+};
+
+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;
+
+	/*
+	 * 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(10);
+	gpiod_set_value(data->gpiod_trig, 0);
+
+	/* it cannot take more than 20 ms */
+	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;
+	}
+
+	ret = wait_for_completion_killable_timeout(&data->falling, HZ/50);
+	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 3 meters is beyond the capabilities of
+	 * the sensor
+	 * ==> filter out invalid results for not measuring echos of
+	 *     another us sensor
+	 *
+	 * formula:
+	 *         distance       3 m
+	 * time = ---------- = --------- = 9404389 ns
+	 *          speed       319 m/s
+	 *
+	 * using a minimum speed at -20 °C of 319 m/s
+	 */
+	if (dt_ns > 9404389)
+		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 m/s as ultrasonic speed at 20 °C here in absence of the
+	 * temperature
+	 *
+	 * therefore:
+	 *             time     343
+	 * distance = ------ * -----
+	 *             10^6       2
+	 *   with time in ns
+	 *   and distance in mm (one way)
+	 *
+	 * because we limit to 3 meters the multiplication with 343 just
+	 * fits into 32 bit
+	 */
+	distance_mm = time_ns * 343 / 2000000;
+
+	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 = {
+	.driver_module		= THIS_MODULE,
+	.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 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;
+
+	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);
+	}
+
+	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->dev.parent = &pdev->dev;
+	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);
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id of_srf04_match[] = {
+	{ .compatible = "devantech,srf04", },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, of_srf04_match);
+
+static struct platform_driver srf04_driver = {
+	.probe		= srf04_probe,
+	.driver		= {
+		.name		= "srf04-gpio",
+		.of_match_table	= of_srf04_match,
+	},
+};
+
+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");