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1// SPDX-License-Identifier: GPL-2.02/*3 * Driver for an envelope detector using a DAC and a comparator4 *5 * Copyright (C) 2016 Axentia Technologies AB6 *7 * Author: Peter Rosin <peda@axentia.se>8 */9 10/*11 * The DAC is used to find the peak level of an alternating voltage input12 * signal by a binary search using the output of a comparator wired to13 * an interrupt pin. Like so:14 * _15 * | \16 * input +------>-------|+ \17 * | \18 * .-------. | }---.19 * | | | / |20 * | dac|-->--|- / |21 * | | |_/ |22 * | | |23 * | | |24 * | irq|------<-------'25 * | |26 * '-------'27 */28 29#include <linux/completion.h>30#include <linux/device.h>31#include <linux/err.h>32#include <linux/kernel.h>33#include <linux/module.h>34#include <linux/mod_devicetable.h>35#include <linux/mutex.h>36#include <linux/iio/consumer.h>37#include <linux/iio/iio.h>38#include <linux/iio/sysfs.h>39#include <linux/interrupt.h>40#include <linux/irq.h>41#include <linux/platform_device.h>42#include <linux/spinlock.h>43#include <linux/workqueue.h>44 45struct envelope {46 spinlock_t comp_lock; /* protects comp */47 int comp;48 49 struct mutex read_lock; /* protects everything else */50 51 int comp_irq;52 u32 comp_irq_trigger;53 u32 comp_irq_trigger_inv;54 55 struct iio_channel *dac;56 struct delayed_work comp_timeout;57 58 unsigned int comp_interval;59 bool invert;60 u32 dac_max;61 62 int high;63 int level;64 int low;65 66 struct completion done;67};68 69/*70 * The envelope_detector_comp_latch function works together with the compare71 * interrupt service routine below (envelope_detector_comp_isr) as a latch72 * (one-bit memory) for if the interrupt has triggered since last calling73 * this function.74 * The ..._comp_isr function disables the interrupt so that the cpu does not75 * need to service a possible interrupt flood from the comparator when no-one76 * cares anyway, and this ..._comp_latch function reenables them again if77 * needed.78 */79static int envelope_detector_comp_latch(struct envelope *env)80{81 int comp;82 83 spin_lock_irq(&env->comp_lock);84 comp = env->comp;85 env->comp = 0;86 spin_unlock_irq(&env->comp_lock);87 88 if (!comp)89 return 0;90 91 /*92 * The irq was disabled, and is reenabled just now.93 * But there might have been a pending irq that94 * happened while the irq was disabled that fires95 * just as the irq is reenabled. That is not what96 * is desired.97 */98 enable_irq(env->comp_irq);99 100 /* So, synchronize this possibly pending irq... */101 synchronize_irq(env->comp_irq);102 103 /* ...and redo the whole dance. */104 spin_lock_irq(&env->comp_lock);105 comp = env->comp;106 env->comp = 0;107 spin_unlock_irq(&env->comp_lock);108 109 if (comp)110 enable_irq(env->comp_irq);111 112 return 1;113}114 115static irqreturn_t envelope_detector_comp_isr(int irq, void *ctx)116{117 struct envelope *env = ctx;118 119 spin_lock(&env->comp_lock);120 env->comp = 1;121 disable_irq_nosync(env->comp_irq);122 spin_unlock(&env->comp_lock);123 124 return IRQ_HANDLED;125}126 127static void envelope_detector_setup_compare(struct envelope *env)128{129 int ret;130 131 /*132 * Do a binary search for the peak input level, and stop133 * when that level is "trapped" between two adjacent DAC134 * values.135 * When invert is active, use the midpoint floor so that136 * env->level ends up as env->low when the termination137 * criteria below is fulfilled, and use the midpoint138 * ceiling when invert is not active so that env->level139 * ends up as env->high in that case.140 */141 env->level = (env->high + env->low + !env->invert) / 2;142 143 if (env->high == env->low + 1) {144 complete(&env->done);145 return;146 }147 148 /* Set a "safe" DAC level (if there is such a thing)... */149 ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);150 if (ret < 0)151 goto err;152 153 /* ...clear the comparison result... */154 envelope_detector_comp_latch(env);155 156 /* ...set the real DAC level... */157 ret = iio_write_channel_raw(env->dac, env->level);158 if (ret < 0)159 goto err;160 161 /* ...and wait for a bit to see if the latch catches anything. */162 schedule_delayed_work(&env->comp_timeout,163 msecs_to_jiffies(env->comp_interval));164 return;165 166err:167 env->level = ret;168 complete(&env->done);169}170 171static void envelope_detector_timeout(struct work_struct *work)172{173 struct envelope *env = container_of(work, struct envelope,174 comp_timeout.work);175 176 /* Adjust low/high depending on the latch content... */177 if (!envelope_detector_comp_latch(env) ^ !env->invert)178 env->low = env->level;179 else180 env->high = env->level;181 182 /* ...and continue the search. */183 envelope_detector_setup_compare(env);184}185 186static int envelope_detector_read_raw(struct iio_dev *indio_dev,187 struct iio_chan_spec const *chan,188 int *val, int *val2, long mask)189{190 struct envelope *env = iio_priv(indio_dev);191 int ret;192 193 switch (mask) {194 case IIO_CHAN_INFO_RAW:195 /*196 * When invert is active, start with high=max+1 and low=0197 * since we will end up with the low value when the198 * termination criteria is fulfilled (rounding down). And199 * start with high=max and low=-1 when invert is not active200 * since we will end up with the high value in that case.201 * This ensures that the returned value in both cases are202 * in the same range as the DAC and is a value that has not203 * triggered the comparator.204 */205 mutex_lock(&env->read_lock);206 env->high = env->dac_max + env->invert;207 env->low = -1 + env->invert;208 envelope_detector_setup_compare(env);209 wait_for_completion(&env->done);210 if (env->level < 0) {211 ret = env->level;212 goto err_unlock;213 }214 *val = env->invert ? env->dac_max - env->level : env->level;215 mutex_unlock(&env->read_lock);216 217 return IIO_VAL_INT;218 219 case IIO_CHAN_INFO_SCALE:220 return iio_read_channel_scale(env->dac, val, val2);221 }222 223 return -EINVAL;224 225err_unlock:226 mutex_unlock(&env->read_lock);227 return ret;228}229 230static ssize_t envelope_show_invert(struct iio_dev *indio_dev,231 uintptr_t private,232 struct iio_chan_spec const *ch, char *buf)233{234 struct envelope *env = iio_priv(indio_dev);235 236 return sprintf(buf, "%u\n", env->invert);237}238 239static ssize_t envelope_store_invert(struct iio_dev *indio_dev,240 uintptr_t private,241 struct iio_chan_spec const *ch,242 const char *buf, size_t len)243{244 struct envelope *env = iio_priv(indio_dev);245 unsigned long invert;246 int ret;247 u32 trigger;248 249 ret = kstrtoul(buf, 0, &invert);250 if (ret < 0)251 return ret;252 if (invert > 1)253 return -EINVAL;254 255 trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;256 257 mutex_lock(&env->read_lock);258 if (invert != env->invert)259 ret = irq_set_irq_type(env->comp_irq, trigger);260 if (!ret) {261 env->invert = invert;262 ret = len;263 }264 mutex_unlock(&env->read_lock);265 266 return ret;267}268 269static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,270 uintptr_t private,271 struct iio_chan_spec const *ch,272 char *buf)273{274 struct envelope *env = iio_priv(indio_dev);275 276 return sprintf(buf, "%u\n", env->comp_interval);277}278 279static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,280 uintptr_t private,281 struct iio_chan_spec const *ch,282 const char *buf, size_t len)283{284 struct envelope *env = iio_priv(indio_dev);285 unsigned long interval;286 int ret;287 288 ret = kstrtoul(buf, 0, &interval);289 if (ret < 0)290 return ret;291 if (interval > 1000)292 return -EINVAL;293 294 mutex_lock(&env->read_lock);295 env->comp_interval = interval;296 mutex_unlock(&env->read_lock);297 298 return len;299}300 301static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {302 { .name = "invert",303 .read = envelope_show_invert,304 .write = envelope_store_invert, },305 { .name = "compare_interval",306 .read = envelope_show_comp_interval,307 .write = envelope_store_comp_interval, },308 { /* sentinel */ }309};310 311static const struct iio_chan_spec envelope_detector_iio_channel = {312 .type = IIO_ALTVOLTAGE,313 .info_mask_separate = BIT(IIO_CHAN_INFO_RAW)314 | BIT(IIO_CHAN_INFO_SCALE),315 .ext_info = envelope_detector_ext_info,316 .indexed = 1,317};318 319static const struct iio_info envelope_detector_info = {320 .read_raw = &envelope_detector_read_raw,321};322 323static int envelope_detector_probe(struct platform_device *pdev)324{325 struct device *dev = &pdev->dev;326 struct iio_dev *indio_dev;327 struct envelope *env;328 enum iio_chan_type type;329 int ret;330 331 indio_dev = devm_iio_device_alloc(dev, sizeof(*env));332 if (!indio_dev)333 return -ENOMEM;334 335 platform_set_drvdata(pdev, indio_dev);336 env = iio_priv(indio_dev);337 env->comp_interval = 50; /* some sensible default? */338 339 spin_lock_init(&env->comp_lock);340 mutex_init(&env->read_lock);341 init_completion(&env->done);342 INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);343 344 indio_dev->name = dev_name(dev);345 indio_dev->info = &envelope_detector_info;346 indio_dev->channels = &envelope_detector_iio_channel;347 indio_dev->num_channels = 1;348 349 env->dac = devm_iio_channel_get(dev, "dac");350 if (IS_ERR(env->dac))351 return dev_err_probe(dev, PTR_ERR(env->dac),352 "failed to get dac input channel\n");353 354 env->comp_irq = platform_get_irq_byname(pdev, "comp");355 if (env->comp_irq < 0)356 return env->comp_irq;357 358 ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr,359 0, "envelope-detector", env);360 if (ret)361 return dev_err_probe(dev, ret, "failed to request interrupt\n");362 363 env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);364 if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)365 env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;366 if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)367 env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;368 if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)369 env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;370 if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)371 env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;372 373 ret = iio_get_channel_type(env->dac, &type);374 if (ret < 0)375 return ret;376 377 if (type != IIO_VOLTAGE) {378 dev_err(dev, "dac is of the wrong type\n");379 return -EINVAL;380 }381 382 ret = iio_read_max_channel_raw(env->dac, &env->dac_max);383 if (ret < 0) {384 dev_err(dev, "dac does not indicate its raw maximum value\n");385 return ret;386 }387 388 return devm_iio_device_register(dev, indio_dev);389}390 391static const struct of_device_id envelope_detector_match[] = {392 { .compatible = "axentia,tse850-envelope-detector", },393 { /* sentinel */ }394};395MODULE_DEVICE_TABLE(of, envelope_detector_match);396 397static struct platform_driver envelope_detector_driver = {398 .probe = envelope_detector_probe,399 .driver = {400 .name = "iio-envelope-detector",401 .of_match_table = envelope_detector_match,402 },403};404module_platform_driver(envelope_detector_driver);405 406MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");407MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");408MODULE_LICENSE("GPL v2");409