Date:   Sat, 22 Oct 2016 16:03:29 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 4/4] iio: envelope-detector: ADC driver based on a DAC and
 a comparator

On 20/10/16 10:26, Peter Rosin wrote:
> The DAC is used to find the peak level of an alternating voltage input
> signal by a binary search using the output of a comparator wired to
> an interrupt pin. Like so:
>                           _
>                          | \
>     input +------>-------|+ \
>                          |   \
>            .-------.     |    }---.
>            |       |     |   /    |
>            |    dac|-->--|- /     |
>            |       |     |_/      |
>            |       |              |
>            |       |              |
>            |    irq|------<-------'
>            |       |
>            '-------'
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
Some really trivial bits inline that might have made it into your V2.

Jonathan
> ---
>  MAINTAINERS                         |   1 +
>  drivers/iio/adc/Kconfig             |  10 ++
>  drivers/iio/adc/Makefile            |   1 +
>  drivers/iio/adc/envelope-detector.c | 305 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 317 insertions(+)
>  create mode 100644 drivers/iio/adc/envelope-detector.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 4b6f6ec1b703..d9a58b5f2b6f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6123,6 +6123,7 @@ M:	Peter Rosin <peda@...ntia.se>
>  L:	linux-iio@...r.kernel.org
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
> +F:	drivers/iio/adc/envelope-detector.c
>  
>  IIO SUBSYSTEM AND DRIVERS
>  M:	Jonathan Cameron <jic23@...nel.org>
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 7edcf3238620..d5c4a95855c2 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -195,6 +195,16 @@ config DA9150_GPADC
>  	  To compile this driver as a module, choose M here: the module will be
>  	  called berlin2-adc.
>  
> +config ENVELOPE_DETECTOR
> +	tristate "Envelope detector using a DAC and a comparator"
> +	depends on OF
> +	help
> +	  Say yes here to build support for an envelope detector using a DAC
> +	  and a comparator.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called iio-envelope-detector.
> +
>  config EXYNOS_ADC
>  	tristate "Exynos ADC driver support"
>  	depends on ARCH_EXYNOS || ARCH_S3C24XX || ARCH_S3C64XX || (OF && COMPILE_TEST)
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index 7a40c04c311f..0d773c6a0578 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -20,6 +20,7 @@ obj-$(CONFIG_BCM_IPROC_ADC) += bcm_iproc_adc.o
>  obj-$(CONFIG_BERLIN2_ADC) += berlin2-adc.o
>  obj-$(CONFIG_CC10001_ADC) += cc10001_adc.o
>  obj-$(CONFIG_DA9150_GPADC) += da9150-gpadc.o
> +obj-$(CONFIG_ENVELOPE_DETECTOR) += envelope-detector.o
>  obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
>  obj-$(CONFIG_FSL_MX25_ADC) += fsl-imx25-gcq.o
>  obj-$(CONFIG_HI8435) += hi8435.o
> diff --git a/drivers/iio/adc/envelope-detector.c b/drivers/iio/adc/envelope-detector.c
> new file mode 100644
> index 000000000000..837646107beb
> --- /dev/null
> +++ b/drivers/iio/adc/envelope-detector.c
> @@ -0,0 +1,305 @@
> +/*
> + * Driver for an envelope detector using a DAC and a comparator
> + *
> + * Copyright (C) 2016 Axentia Technologies AB
> + *
> + * Author: Peter Rosin <peda@...ntia.se>
> + *
> + * 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.
> + */
> +
> +/*
> + * The DAC is used to find the peak level of an alternating voltage input
> + * signal by a binary search using the output of a comparator wired to
> + * an interrupt pin. Like so:
> + *                           _
> + *                          | \
> + *     input +------>-------|+ \
> + *                          |   \
> + *            .-------.     |    }---.
> + *            |       |     |   /    |
> + *            |    dac|-->--|- /     |
> + *            |       |     |_/      |
> + *            |       |              |
> + *            |       |              |
> + *            |    irq|------<-------'
> + *            |       |
> + *            '-------'
> + */
> +
> +#include <linux/completion.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/interrupt.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/spinlock.h>
> +#include <linux/workqueue.h>
> +
> +struct envelope {
> +	struct iio_channel *dac;
> +	struct delayed_work comp_timeout;
> +	int comp_irq;
> +
> +	spinlock_t comp_lock; /* protects comp */
> +	int comp;
> +
> +	struct mutex read_lock; /* protects everything below */
> +
> +	u32 dac_max;
> +	u32 comp_interval;
> +	bool invert;
> +
> +	int high;
> +	int level;
> +	int low;
> +
> +	struct completion done;
> +};
> +
Perhaps a comment explaining what this function is doing..
The naming isn't 100% clear...
> +static int envelope_detector_latch(struct envelope *env)
> +{
> +	int comp;
> +
> +	spin_lock_irq(&env->comp_lock);
> +	comp = env->comp;
> +	env->comp = 0;
> +	spin_unlock_irq(&env->comp_lock);
> +
> +	if (comp)
> +		enable_irq(env->comp_irq);
> +
> +	return comp;
> +}
> +
> +static irqreturn_t envelope_detector_isr(int irq, void *ctx)
> +{
> +	struct envelope *env = ctx;
> +
> +	spin_lock(&env->comp_lock);
> +	env->comp = 1;
> +	disable_irq_nosync(env->comp_irq);
> +	spin_unlock(&env->comp_lock);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void envelope_detector_setup_compare(struct envelope *env)
> +{
> +	int ret;
> +
> +	/*
> +	 * Do a binary search for the peak input level, and stop
> +	 * when that level is "trapped" between two adjacent DAC
> +	 * values.
> +	 * When invert is active, use the midpoint floor so that
> +	 * env->level ends up as env->low when the termination
> +	 * criteria below is fulfilled, and use the midpoint
> +	 * ceiling when invert is not active so that env->level
> +	 * ends up as env->high in that case.
> +	 */
> +	env->level = (env->high + env->low + !env->invert) / 2;
> +
> +	if (env->high == env->low + 1) {
> +		complete(&env->done);
> +		return;
> +	}
> +
> +	/* Set a "safe" DAC level (if there is such a thing)... */
> +	ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);
> +	if (ret < 0)
> +		goto err;
> +
> +	/* ...clear the comparison result... */
> +	envelope_detector_latch(env);
> +
> +	/* ...set the real DAC level... */
> +	ret = iio_write_channel_raw(env->dac, env->level);
> +	if (ret < 0)
> +		goto err;
> +
> +	/* ...and wait for a bit to see if the latch catches anything. */
> +	schedule_delayed_work(&env->comp_timeout,
> +			      msecs_to_jiffies(env->comp_interval));
> +	return;
> +
> +err:
> +	env->level = ret;
> +	complete(&env->done);
> +}
> +
> +static void envelope_detector_timeout(struct work_struct *work)
> +{
> +	struct envelope *env = container_of(work, struct envelope,
> +					    comp_timeout.work);
> +
> +	/* Adjust low/high depending on the latch content... */
> +	if (!envelope_detector_latch(env) ^ !env->invert)
> +		env->low = env->level;
> +	else
> +		env->high = env->level;
> +
> +	/* ...and continue the search. */
> +	envelope_detector_setup_compare(env);
> +}
> +
> +static int envelope_detector_read_raw(struct iio_dev *indio_dev,
> +				      struct iio_chan_spec const *chan,
> +				      int *val, int *val2, long mask)
> +{
> +	struct envelope *env = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		/*
> +		 * When invert is active, start with high=max+1 and low=0
> +		 * since we will end up with the low value when the
> +		 * termination criteria is fulfilled (rounding down). And
> +		 * start with high=max and low=-1 when invert is not active
> +		 * since we will end up with the high value in that case.
> +		 * This ensures that we in both cases return a value in the
> +		 * same range as the DAC and that as not triggered the
has

Impressive level of detail. I'd probably have missed the need for this!
> +		 * comparator.
> +		 */
> +		mutex_lock(&env->read_lock);
> +		env->high = env->dac_max + 1 - !env->invert;
> +		env->low = 0 - !env->invert;
> +		envelope_detector_setup_compare(env);
> +		wait_for_completion(&env->done);
> +		if (env->level < 0) {
> +			ret = env->level;
> +			goto err_unlock;
> +		}
> +		*val = env->invert ? env->dac_max - env->level : env->level;
> +		mutex_unlock(&env->read_lock);
> +
> +		return IIO_VAL_INT;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		return iio_read_channel_scale(env->dac, val, val2);
> +	}
> +
> +	return -EINVAL;
> +
> +err_unlock:
> +	mutex_unlock(&env->read_lock);
> +	return ret;
> +}
> +
> +static const struct iio_chan_spec envelope_detector_iio_channel = {
> +	.type = IIO_ALTVOLTAGE,
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
> +			    | BIT(IIO_CHAN_INFO_SCALE),
> +	.output = 1,
> +};
> +
> +static const struct iio_info envelope_detector_info = {
> +	.read_raw = &envelope_detector_read_raw,
> +	.driver_module = THIS_MODULE,
> +};
> +
> +static int envelope_detector_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct iio_dev *indio_dev;
> +	struct envelope *env;
> +	enum iio_chan_type type;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*env));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, indio_dev);
> +	env = iio_priv(indio_dev);
> +
> +	spin_lock_init(&env->comp_lock);
> +	mutex_init(&env->read_lock);
> +	init_completion(&env->done);
> +	INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);
> +
> +	indio_dev->name = dev_name(dev);
> +	indio_dev->dev.parent = dev;
> +	indio_dev->dev.of_node = dev->of_node;
> +	indio_dev->info = &envelope_detector_info;
> +	indio_dev->channels = &envelope_detector_iio_channel;
> +	indio_dev->num_channels = 1;
> +
> +	env->dac = devm_iio_channel_get(dev, "dac");
> +	if (IS_ERR(env->dac)) {
> +		if (PTR_ERR(env->dac) != -EPROBE_DEFER)
> +			dev_err(dev, "failed to get dac input channel\n");
> +		return PTR_ERR(env->dac);
> +	}
> +
> +	env->comp_irq = platform_get_irq_byname(pdev, "comp");
> +	if (env->comp_irq < 0) {
> +		if (env->comp_irq != -EPROBE_DEFER)
> +			dev_err(dev, "failed to get compare interrupt\n");
> +		return env->comp_irq;
> +	}
> +
> +	ret = devm_request_irq(dev, env->comp_irq, envelope_detector_isr, 0,
> +			       "env-env-dac-comp", env);
> +	if (ret) {
> +		if (ret != -EPROBE_DEFER)
> +			dev_err(dev, "failed to request interrupt\n");
> +		return ret;
> +	}
> +
> +	ret = iio_get_channel_type(env->dac, &type);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (type != IIO_VOLTAGE) {
> +		dev_err(dev, "dac is of the wrong type\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = of_property_read_u32(dev->of_node, "envelope-detector,dac-max",
> +				   &env->dac_max);
> +	if (ret) {
> +		dev_err(dev, "the dac-max property is missing\n");
> +		return ret;
> +	}
> +
> +	ret = of_property_read_u32(dev->of_node,
> +				   "envelope-detector,comp-interval-ms",
> +				   &env->comp_interval);
> +	if (ret) {
> +		dev_err(dev, "the comp-interval-ms property is missing\n");
> +		return ret;
> +	}
> +
> +	env->invert = of_property_read_bool(dev->of_node,
> +					    "envelope-detector,inverted");
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
> +static const struct of_device_id envelope_detector_match[] = {
> +	{ .compatible = "envelope-detector" },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, envelope_detector_match);
> +
> +static struct platform_driver envelope_detector_driver = {
> +	.probe = envelope_detector_probe,
> +	.driver = {
> +		.name = "iio-envelope-detector",
> +		.of_match_table = envelope_detector_match,
> +	},
> +};
> +module_platform_driver(envelope_detector_driver);
> +
> +MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
> +MODULE_AUTHOR("Peter Rosin <peda@...ntia.se>");
> +MODULE_LICENSE("GPL v2");
> 

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