409 lines
11 KiB
C
409 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Driver for an envelope detector using a DAC and a comparator
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*
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* Copyright (C) 2016 Axentia Technologies AB
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*
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* Author: Peter Rosin <peda@axentia.se>
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*/
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/*
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* The DAC is used to find the peak level of an alternating voltage input
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* signal by a binary search using the output of a comparator wired to
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* an interrupt pin. Like so:
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* _
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* | \
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* input +------>-------|+ \
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* | \
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* .-------. | }---.
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* | | | / |
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* | dac|-->--|- / |
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* | | |_/ |
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* | | |
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* | | |
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* | irq|------<-------'
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* | |
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* '-------'
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*/
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#include <linux/completion.h>
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#include <linux/device.h>
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#include <linux/err.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/mod_devicetable.h>
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#include <linux/mutex.h>
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#include <linux/iio/consumer.h>
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#include <linux/iio/iio.h>
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#include <linux/iio/sysfs.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
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#include <linux/platform_device.h>
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#include <linux/spinlock.h>
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#include <linux/workqueue.h>
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struct envelope {
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spinlock_t comp_lock; /* protects comp */
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int comp;
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struct mutex read_lock; /* protects everything else */
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int comp_irq;
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u32 comp_irq_trigger;
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u32 comp_irq_trigger_inv;
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struct iio_channel *dac;
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struct delayed_work comp_timeout;
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unsigned int comp_interval;
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bool invert;
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u32 dac_max;
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int high;
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int level;
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int low;
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struct completion done;
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};
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/*
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* The envelope_detector_comp_latch function works together with the compare
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* interrupt service routine below (envelope_detector_comp_isr) as a latch
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* (one-bit memory) for if the interrupt has triggered since last calling
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* this function.
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* The ..._comp_isr function disables the interrupt so that the cpu does not
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* need to service a possible interrupt flood from the comparator when no-one
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* cares anyway, and this ..._comp_latch function reenables them again if
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* needed.
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*/
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static int envelope_detector_comp_latch(struct envelope *env)
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{
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int comp;
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spin_lock_irq(&env->comp_lock);
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comp = env->comp;
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env->comp = 0;
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spin_unlock_irq(&env->comp_lock);
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if (!comp)
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return 0;
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/*
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* The irq was disabled, and is reenabled just now.
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* But there might have been a pending irq that
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* happened while the irq was disabled that fires
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* just as the irq is reenabled. That is not what
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* is desired.
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*/
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enable_irq(env->comp_irq);
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/* So, synchronize this possibly pending irq... */
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synchronize_irq(env->comp_irq);
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/* ...and redo the whole dance. */
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spin_lock_irq(&env->comp_lock);
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comp = env->comp;
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env->comp = 0;
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spin_unlock_irq(&env->comp_lock);
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if (comp)
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enable_irq(env->comp_irq);
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return 1;
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}
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static irqreturn_t envelope_detector_comp_isr(int irq, void *ctx)
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{
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struct envelope *env = ctx;
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spin_lock(&env->comp_lock);
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env->comp = 1;
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disable_irq_nosync(env->comp_irq);
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spin_unlock(&env->comp_lock);
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return IRQ_HANDLED;
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}
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static void envelope_detector_setup_compare(struct envelope *env)
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{
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int ret;
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/*
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* Do a binary search for the peak input level, and stop
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* when that level is "trapped" between two adjacent DAC
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* values.
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* When invert is active, use the midpoint floor so that
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* env->level ends up as env->low when the termination
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* criteria below is fulfilled, and use the midpoint
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* ceiling when invert is not active so that env->level
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* ends up as env->high in that case.
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*/
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env->level = (env->high + env->low + !env->invert) / 2;
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if (env->high == env->low + 1) {
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complete(&env->done);
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return;
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}
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/* Set a "safe" DAC level (if there is such a thing)... */
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ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);
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if (ret < 0)
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goto err;
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/* ...clear the comparison result... */
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envelope_detector_comp_latch(env);
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/* ...set the real DAC level... */
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ret = iio_write_channel_raw(env->dac, env->level);
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if (ret < 0)
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goto err;
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/* ...and wait for a bit to see if the latch catches anything. */
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schedule_delayed_work(&env->comp_timeout,
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msecs_to_jiffies(env->comp_interval));
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return;
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err:
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env->level = ret;
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complete(&env->done);
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}
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static void envelope_detector_timeout(struct work_struct *work)
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{
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struct envelope *env = container_of(work, struct envelope,
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comp_timeout.work);
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/* Adjust low/high depending on the latch content... */
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if (!envelope_detector_comp_latch(env) ^ !env->invert)
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env->low = env->level;
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else
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env->high = env->level;
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/* ...and continue the search. */
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envelope_detector_setup_compare(env);
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}
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static int envelope_detector_read_raw(struct iio_dev *indio_dev,
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struct iio_chan_spec const *chan,
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int *val, int *val2, long mask)
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{
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struct envelope *env = iio_priv(indio_dev);
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int ret;
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switch (mask) {
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case IIO_CHAN_INFO_RAW:
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/*
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* When invert is active, start with high=max+1 and low=0
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* since we will end up with the low value when the
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* termination criteria is fulfilled (rounding down). And
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* start with high=max and low=-1 when invert is not active
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* since we will end up with the high value in that case.
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* This ensures that the returned value in both cases are
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* in the same range as the DAC and is a value that has not
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* triggered the comparator.
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*/
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mutex_lock(&env->read_lock);
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env->high = env->dac_max + env->invert;
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env->low = -1 + env->invert;
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envelope_detector_setup_compare(env);
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wait_for_completion(&env->done);
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if (env->level < 0) {
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ret = env->level;
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goto err_unlock;
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}
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*val = env->invert ? env->dac_max - env->level : env->level;
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mutex_unlock(&env->read_lock);
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return IIO_VAL_INT;
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case IIO_CHAN_INFO_SCALE:
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return iio_read_channel_scale(env->dac, val, val2);
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}
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return -EINVAL;
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err_unlock:
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mutex_unlock(&env->read_lock);
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return ret;
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}
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static ssize_t envelope_show_invert(struct iio_dev *indio_dev,
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uintptr_t private,
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struct iio_chan_spec const *ch, char *buf)
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{
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struct envelope *env = iio_priv(indio_dev);
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return sprintf(buf, "%u\n", env->invert);
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}
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static ssize_t envelope_store_invert(struct iio_dev *indio_dev,
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uintptr_t private,
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struct iio_chan_spec const *ch,
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const char *buf, size_t len)
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{
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struct envelope *env = iio_priv(indio_dev);
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unsigned long invert;
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int ret;
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u32 trigger;
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ret = kstrtoul(buf, 0, &invert);
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if (ret < 0)
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return ret;
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if (invert > 1)
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return -EINVAL;
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trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;
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mutex_lock(&env->read_lock);
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if (invert != env->invert)
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ret = irq_set_irq_type(env->comp_irq, trigger);
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if (!ret) {
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env->invert = invert;
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ret = len;
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}
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mutex_unlock(&env->read_lock);
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return ret;
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}
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static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,
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uintptr_t private,
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struct iio_chan_spec const *ch,
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char *buf)
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{
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struct envelope *env = iio_priv(indio_dev);
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return sprintf(buf, "%u\n", env->comp_interval);
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}
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static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,
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uintptr_t private,
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struct iio_chan_spec const *ch,
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const char *buf, size_t len)
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{
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struct envelope *env = iio_priv(indio_dev);
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unsigned long interval;
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int ret;
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ret = kstrtoul(buf, 0, &interval);
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if (ret < 0)
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return ret;
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if (interval > 1000)
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return -EINVAL;
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mutex_lock(&env->read_lock);
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env->comp_interval = interval;
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mutex_unlock(&env->read_lock);
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return len;
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}
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static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {
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{ .name = "invert",
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.read = envelope_show_invert,
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.write = envelope_store_invert, },
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{ .name = "compare_interval",
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.read = envelope_show_comp_interval,
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.write = envelope_store_comp_interval, },
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{ /* sentinel */ }
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};
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static const struct iio_chan_spec envelope_detector_iio_channel = {
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.type = IIO_ALTVOLTAGE,
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.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
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| BIT(IIO_CHAN_INFO_SCALE),
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.ext_info = envelope_detector_ext_info,
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.indexed = 1,
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};
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static const struct iio_info envelope_detector_info = {
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.read_raw = &envelope_detector_read_raw,
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};
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static int envelope_detector_probe(struct platform_device *pdev)
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{
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struct device *dev = &pdev->dev;
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struct iio_dev *indio_dev;
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struct envelope *env;
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enum iio_chan_type type;
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int ret;
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indio_dev = devm_iio_device_alloc(dev, sizeof(*env));
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if (!indio_dev)
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return -ENOMEM;
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platform_set_drvdata(pdev, indio_dev);
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env = iio_priv(indio_dev);
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env->comp_interval = 50; /* some sensible default? */
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spin_lock_init(&env->comp_lock);
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mutex_init(&env->read_lock);
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init_completion(&env->done);
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INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);
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indio_dev->name = dev_name(dev);
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indio_dev->info = &envelope_detector_info;
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indio_dev->channels = &envelope_detector_iio_channel;
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indio_dev->num_channels = 1;
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env->dac = devm_iio_channel_get(dev, "dac");
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if (IS_ERR(env->dac))
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return dev_err_probe(dev, PTR_ERR(env->dac),
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"failed to get dac input channel\n");
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env->comp_irq = platform_get_irq_byname(pdev, "comp");
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if (env->comp_irq < 0)
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return env->comp_irq;
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ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr,
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0, "envelope-detector", env);
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if (ret)
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return dev_err_probe(dev, ret, "failed to request interrupt\n");
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env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);
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if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)
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env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;
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if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)
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env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;
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if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)
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env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;
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if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)
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env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;
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ret = iio_get_channel_type(env->dac, &type);
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if (ret < 0)
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return ret;
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if (type != IIO_VOLTAGE) {
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dev_err(dev, "dac is of the wrong type\n");
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return -EINVAL;
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}
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ret = iio_read_max_channel_raw(env->dac, &env->dac_max);
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if (ret < 0) {
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dev_err(dev, "dac does not indicate its raw maximum value\n");
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return ret;
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}
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return devm_iio_device_register(dev, indio_dev);
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}
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static const struct of_device_id envelope_detector_match[] = {
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{ .compatible = "axentia,tse850-envelope-detector", },
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(of, envelope_detector_match);
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static struct platform_driver envelope_detector_driver = {
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.probe = envelope_detector_probe,
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.driver = {
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.name = "iio-envelope-detector",
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.of_match_table = envelope_detector_match,
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},
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};
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module_platform_driver(envelope_detector_driver);
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MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
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MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
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MODULE_LICENSE("GPL v2");
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