/*
 * 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 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,
};

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@axentia.se>");
MODULE_LICENSE("GPL v2");