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Date:   Sun, 29 Jan 2017 10:11:43 +0100 (CET)
From:   Peter Meerwald-Stadler <pmeerw@...erw.net>
To:     Andreas Klinger <ak@...klinger.de>
cc:     jic23@...nel.org, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: distance: add devantech us ranger srf04


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

comments below
 
> 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 when the measurement should start
>   - echo: set when the ultrasonic wave is sent out and reset when the echo
>     is recognized; 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@...klinger.de>
> ---
>  MAINTAINERS                    |   6 +
>  drivers/iio/proximity/Kconfig  |  11 ++
>  drivers/iio/proximity/Makefile |   1 +
>  drivers/iio/proximity/srf04.c  | 269 +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 287 insertions(+)
>  create mode 100644 drivers/iio/proximity/srf04.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fa6af014fd72..ba979cc48fd8 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3469,6 +3469,12 @@ 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@...klinger.de>
> +L:	linux-iio@...r.kernel.org
> +S:	Maintained
> +F:	drivers/iio/proximity/srf*.c
> +
>  DEVICE COREDUMP (DEV_COREDUMP)
>  M:	Johannes Berg <johannes@...solutions.net>
>  L:	linux-kernel@...r.kernel.org
> diff --git a/drivers/iio/proximity/Kconfig b/drivers/iio/proximity/Kconfig
> index ef4c73db5b53..0bcbc66eae6e 100644
> --- a/drivers/iio/proximity/Kconfig
> +++ b/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
> diff --git a/drivers/iio/proximity/Makefile b/drivers/iio/proximity/Makefile
> index 9aadd9a8ee99..97c046c1dfc5 100644
> --- a/drivers/iio/proximity/Makefile
> +++ b/drivers/iio/proximity/Makefile
> @@ -5,4 +5,5 @@
>  # 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_SX9500)		+= sx9500.o
> diff --git a/drivers/iio/proximity/srf04.c b/drivers/iio/proximity/srf04.c
> new file mode 100644
> index 000000000000..f458c3d9084b
> --- /dev/null
> +++ b/drivers/iio/proximity/srf04.c
> @@ -0,0 +1,269 @@
> +/*
> + * SRF04: ultrasonic sensor for distance measuring by using GPIOs
> + *
> + * Copyright (c) 2017 Andreas Klinger <ak@...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
> + */
> +#include <linux/err.h>
> +#include <linux/gpio.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/bitops.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);
> +
> +	if (gpiod_get_value(data->gpiod_echo)) {
> +		data->ts_rising = ktime_get();
> +		complete(&data->rising);
> +	} else {
> +		data->ts_falling = ktime_get();
> +		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;
> +	u32 distance_mm;
> +
> +	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);
> +
> +	mutex_unlock(&data->lock);
> +
> +	/* it cannot take more than 20 ms */
> +	ret = wait_for_completion_killable_timeout(&data->rising, HZ/50);
> +	if (ret < 0)
> +		return -ETIMEDOUT;
> +
> +	ret = wait_for_completion_killable_timeout(&data->falling, HZ/50);
> +	if (ret < 0)
> +		return -ETIMEDOUT;
> +
> +	ktime_dt = ktime_sub(data->ts_falling, data->ts_rising);
> +
> +	dt_ns = ktime_to_ns(ktime_dt);
> +	/*
> +	 * measuring more than 3 meters is beyond the posibilities of

possibilities, maybe better capabilities

> +	 * the sensor
> +	 */
> +	if (dt_ns > 8750000) {

magic value?
parenthesis {} not needed

> +		return -EFAULT;
> +	}
> +	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:
> +	 * distance = time / 10^6 * 343 / 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;
> +
> +	dev_info (data->dev, "ns: %llu, dist: %d\n", dt_ns, distance_mm);

this should be dbg I think; and no space after dev_info

> +
> +	return distance_mm;
> +}
> +
> +static int srf04_read_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *channel, int *val,
> +			    int *val2, long mask)
> +{
> +	struct srf04_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (channel->type != IIO_DISTANCE)
> +		return -EINVAL;
> +
> +	switch (mask) {
> +	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 = NULL;
> +	struct iio_dev *indio_dev;
> +	int ret = 0;

initialization not needed

> +
> +	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-gpiod: 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-gpiod: 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", ret);

ret? should be data->irqnr?

> +		return ret;
> +	}
> +
> +	ret = request_irq(data->irqnr, srf04_handle_irq,

could use devm_

> +			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);

you can't use devm_iio_device_register() if you need/have a _remove()

> +}
> +
> +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); // (but not needed anymore)

> +	struct srf04_data *data = NULL;
> +	struct iio_dev *indio_dev;
> +
> +	indio_dev = platform_get_drvdata(pdev);
> +	data = iio_priv(indio_dev);
> +
> +	free_irq(data->irqnr, indio_dev);

I suggest to use in _probe()
devm_request_irq()
iio_device_register()

and in _remove() just
iio_device_unregister()

> +
> +	return 0;
> +}
> +
> +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,
> +	.remove		= srf04_remove,
> +	.driver		= {
> +		.name		= "srf04-gpio",
> +		.of_match_table	= of_srf04_match,
> +	},
> +};
> +
> +module_platform_driver(srf04_driver);
> +
> +MODULE_AUTHOR("Andreas Klinger <ak@...klinger.de>");
> +MODULE_DESCRIPTION("SRF04 ultrasonic sensor for distance measuring using GPIOs");
> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:srf04");
> 

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)

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