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    Subject[PATCH v2 7/7] iio: envelope-detector: ADC driver based on a DAC and a comparator
    Date
    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@axentia.se>
    ---
    .../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 | 463 +++++++++++++++++++++
    5 files changed, 512 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..8d890028a649
    --- /dev/null
    +++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
    @@ -0,0 +1,36 @@
    +What: /sys/bus/iio/devices/iio:deviceX/invert
    +Date: October 2016
    +KernelVersion: 4.9
    +Contact: Peter Rosin <peda@axentia.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/compare_interval_ms
    +Date: October 2016
    +KernelVersion: 4.9
    +Contact: Peter Rosin <peda@axentia.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 4b6f6ec1b703..0d20f3561700 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -6122,7 +6122,9 @@ IIO ENVELOPE DETECTOR
    M: Peter Rosin <peda@axentia.se>
    L: linux-iio@vger.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@kernel.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..3842d1a72023
    --- /dev/null
    +++ b/drivers/iio/adc/envelope-detector.c
    @@ -0,0 +1,463 @@
    +/*
    + * Driver for an envelope detector using a DAC and a comparator
    + *
    + * Copyright (C) 2016 Axentia Technologies AB
    + *
    + * Author: Peter Rosin <peda@axentia.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 int envelope_detector_channel_raw_max(struct iio_channel *ch)
    +{
    + struct iio_dev *indio_dev = ch->indio_dev;
    + const int *vals;
    + int type;
    + int len;
    + int ret;
    +
    + if (!ch->indio_dev->info->read_avail)
    + return -EINVAL;
    +
    + ret = ch->indio_dev->info->read_avail(indio_dev, ch->channel,
    + &vals, &type, &len,
    + IIO_CHAN_INFO_RAW);
    +
    + if (ret < 0)
    + return ret;
    + if (type != IIO_VAL_INT)
    + return -EINVAL;
    +
    + switch (ret) {
    + case IIO_AVAIL_RANGE:
    + if (len != 3)
    + return -EINVAL;
    + return vals[2];
    + }
    + return -EINVAL;
    +}
    +
    +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),
    + .indexed = 1,
    +};
    +
    +static ssize_t envelope_show_invert(struct device *dev,
    + struct device_attribute *attr,
    + char *buf)
    +{
    + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
    + struct envelope *env = iio_priv(indio_dev);
    +
    + return sprintf(buf, "%u\n", env->invert);
    +}
    +
    +static ssize_t envelope_store_invert(struct device *dev,
    + struct device_attribute *attr,
    + const char *buf,
    + size_t len)
    +{
    + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
    + 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 IIO_DEVICE_ATTR(invert, 0644,
    + envelope_show_invert,
    + envelope_store_invert, 0);
    +
    +static ssize_t envelope_show_comp_interval(struct device *dev,
    + struct device_attribute *attr,
    + char *buf)
    +{
    + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
    + struct envelope *env = iio_priv(indio_dev);
    +
    + return sprintf(buf, "%u\n", env->comp_interval);
    +}
    +
    +static ssize_t envelope_store_comp_interval(struct device *dev,
    + struct device_attribute *attr,
    + const char *buf,
    + size_t len)
    +{
    + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
    + 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 IIO_DEVICE_ATTR(compare_interval_ms, 0644,
    + envelope_show_comp_interval,
    + envelope_store_comp_interval, 0);
    +
    +static struct attribute *envelope_detector_attributes[] = {
    + &iio_dev_attr_invert.dev_attr.attr,
    + &iio_dev_attr_compare_interval_ms.dev_attr.attr,
    + NULL,
    +};
    +
    +static const struct attribute_group envelope_detector_attribute_group = {
    + .attrs = envelope_detector_attributes,
    +};
    +
    +static const struct iio_info envelope_detector_info = {
    + .read_raw = &envelope_detector_read_raw,
    + .driver_module = THIS_MODULE,
    + .attrs = &envelope_detector_attribute_group,
    +};
    +
    +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 = envelope_detector_channel_raw_max(env->dac);
    + if (ret < 0) {
    + dev_err(dev, "dac does not indicate its raw maximum value\n");
    + return ret;
    + }
    + env->dac_max = 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@axentia.se>");
    +MODULE_LICENSE("GPL v2");
    --
    2.1.4
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      Last update: 2016-10-23 05:20    [W:2.557 / U:0.308 seconds]
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