Date:   Sun, 30 Oct 2016 13:44:48 +0000
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, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 8/8] iio: envelope-detector: ADC driver based on a DAC
 and a comparator

On 23/10/16 23:39, 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>
Looks good to me.  I've cc'd Thomas Gleixner as the irq usage is obviously
a bit unusual and I thought he may have some thoughts on it.

Jonathan
> ---
>  .../testing/sysfs-bus-iio-adc-envelope-detector    |  36 ++
>  MAINTAINERS                                        |   2 +
>  drivers/iio/adc/Kconfig                            |  10 +
>  drivers/iio/adc/Makefile                           |   1 +
>  drivers/iio/adc/envelope-detector.c                | 422 +++++++++++++++++++++
>  5 files changed, 471 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>  create mode 100644 drivers/iio/adc/envelope-detector.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector b/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
> new file mode 100644
> index 000000000000..2071f9bcfaa5
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
> @@ -0,0 +1,36 @@
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltageY_invert
> +Date:		October 2016
> +KernelVersion:	4.9
> +Contact:	Peter Rosin <peda@...ntia.se>
> +Description:
> +		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|------<-------'
> +		            |       |
> +		            '-------'
> +		The boolean invert attribute (0/1) should be set when the
> +		input signal is centered around the maximum value of the
> +		dac instead of zero. The envelope detector will search
> +		from below in this case and will also invert the result.
> +		The edge/level of the interrupt is also switched to its
> +		opposite value.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_altvoltageY_compare_interval
> +Date:		October 2016
> +KernelVersion:	4.9
> +Contact:	Peter Rosin <peda@...ntia.se>
> +Description:
> +		Number of milliseconds to wait for the comparator in each
> +		step of the binary search for the input peak level. Needs
> +		to relate to the frequency of the input signal.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fca35d16037d..0cf3549e05e7 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -6123,7 +6123,9 @@ IIO ENVELOPE DETECTOR
>  M:	Peter Rosin <peda@...ntia.se>
>  L:	linux-iio@...r.kernel.org
>  S:	Maintained
> +F:	Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
>  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..fef15c0d7c9c
> --- /dev/null
> +++ b/drivers/iio/adc/envelope-detector.c
> @@ -0,0 +1,422 @@
> +/*
> + * 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/iio/sysfs.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/spinlock.h>
> +#include <linux/workqueue.h>
> +
> +struct envelope {
> +	spinlock_t comp_lock; /* protects comp */
> +	int comp;
> +
> +	struct mutex read_lock; /* protects everything else */
> +
> +	int comp_irq;
> +	u32 comp_irq_trigger;
> +	u32 comp_irq_trigger_inv;
> +
> +	struct iio_channel *dac;
> +	struct delayed_work comp_timeout;
> +
> +	unsigned int comp_interval;
> +	bool invert;
> +	u32 dac_max;
> +
> +	int high;
> +	int level;
> +	int low;
> +
> +	struct completion done;
> +};
> +
> +/*
> + * The envelope_detector_comp_latch function works together with the compare
> + * interrupt service routine below (envelope_detector_comp_isr) as a latch
> + * (one-bit memory) for if the interrupt has triggered since last calling
> + * this function.
> + * The ..._comp_isr function disables the interrupt so that the cpu does not
> + * need to service a possible interrupt flood from the comparator when no-one
> + * cares anyway, and this ..._comp_latch function reenables them again if
> + * needed.
> + */
> +static int envelope_detector_comp_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)
> +		return 0;
> +
> +	/*
> +	 * The irq was disabled, and is reenabled just now.
> +	 * But there might have been a pending irq that
> +	 * happened while the irq was disabled that fires
> +	 * just as the irq is reenabled. That is not what
> +	 * is desired.
> +	 */
> +	enable_irq(env->comp_irq);
> +
> +	/* So, synchronize this possibly pending irq... */
> +	synchronize_irq(env->comp_irq);
> +
> +	/* ...and redo the whole dance. */
> +	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 1;
> +}
> +
> +static irqreturn_t envelope_detector_comp_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_comp_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_comp_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 the returned value in both cases are
> +		 * in the same range as the DAC and is a value that has not
> +		 * triggered the comparator.
> +		 */
> +		mutex_lock(&env->read_lock);
> +		env->high = env->dac_max + env->invert;
> +		env->low = -1 + 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 ssize_t envelope_show_invert(struct iio_dev *indio_dev,
> +				    uintptr_t private,
> +				    struct iio_chan_spec const *ch, char *buf)
> +{
> +	struct envelope *env = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%u\n", env->invert);
> +}
> +
> +static ssize_t envelope_store_invert(struct iio_dev *indio_dev,
> +				     uintptr_t private,
> +				     struct iio_chan_spec const *ch,
> +				     const char *buf, size_t len)
> +{
> +	struct envelope *env = iio_priv(indio_dev);
> +	unsigned long invert;
> +	int ret;
> +	u32 trigger;
> +
> +	ret = kstrtoul(buf, 0, &invert);
> +	if (ret < 0)
> +		return ret;
> +	if (invert > 1)
> +		return -EINVAL;
> +
> +	trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;
> +
> +	mutex_lock(&env->read_lock);
> +	if (invert != env->invert)
> +		ret = irq_set_irq_type(env->comp_irq, trigger);
> +	if (!ret) {
> +		env->invert = invert;
> +		ret = len;
> +	}
> +	mutex_unlock(&env->read_lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,
> +					   uintptr_t private,
> +					   struct iio_chan_spec const *ch,
> +					   char *buf)
> +{
> +	struct envelope *env = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%u\n", env->comp_interval);
> +}
> +
> +static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,
> +					    uintptr_t private,
> +					    struct iio_chan_spec const *ch,
> +					    const char *buf, size_t len)
> +{
> +	struct envelope *env = iio_priv(indio_dev);
> +	unsigned long interval;
> +	int ret;
> +
> +	ret = kstrtoul(buf, 0, &interval);
> +	if (ret < 0)
> +		return ret;
> +	if (interval > 1000)
> +		return -EINVAL;
> +
> +	mutex_lock(&env->read_lock);
> +	env->comp_interval = interval;
> +	mutex_unlock(&env->read_lock);
> +
> +	return len;
> +}
> +
> +static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {
> +	{ .name = "invert",
> +	  .read = envelope_show_invert,
> +	  .write = envelope_store_invert, },
> +	{ .name = "compare_interval",
> +	  .read = envelope_show_comp_interval,
> +	  .write = envelope_store_comp_interval, },
> +	{ /* sentinel */ }
> +};
> +
> +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),
> +	.ext_info = envelope_detector_ext_info,
> +	.indexed = 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);
> +	env->comp_interval = 50; /* some sensible default? */
> +
> +	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_comp_isr,
> +			       0, "envelope-detector", env);
> +	if (ret) {
> +		if (ret != -EPROBE_DEFER)
> +			dev_err(dev, "failed to request interrupt\n");
> +		return ret;
> +	}
> +	env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);
> +	if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)
> +		env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;
> +	if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)
> +		env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;
> +	if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)
> +		env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;
> +	if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)
> +		env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;
> +
> +	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 = iio_read_max_channel_raw(env->dac, &env->dac_max);
> +	if (ret < 0) {
> +		dev_err(dev, "dac does not indicate its raw maximum value\n");
> +		return ret;
> +	}
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
> +static const struct of_device_id envelope_detector_match[] = {
> +	{ .compatible = "axentia,tse850-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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