linux/drivers/iio/adc/envelope-detector.c

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