drivers/iio/adc/envelope-detector.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Driver for an envelope detector using a DAC and a comparator
   4  *
   5  * Copyright (C) 2016 Axentia Technologies AB
   6  *
   7  * Author: Peter Rosin <peda@axentia.se>
   8  */
   9
  10 /*
  11  * The DAC is used to find the peak level of an alternating voltage input
  12  * signal by a binary search using the output of a comparator wired to
  13  * 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/mutex.h>
  35 #include <linux/iio/consumer.h>
  36 #include <linux/iio/iio.h>
  37 #include <linux/iio/sysfs.h>
  38 #include <linux/interrupt.h>
  39 #include <linux/irq.h>
  40 #include <linux/of.h>
  41 #include <linux/of_device.h>
  42 #include <linux/platform_device.h>
  43 #include <linux/spinlock.h>
  44 #include <linux/workqueue.h>
  45
  46 struct envelope {
  47         spinlock_t comp_lock; /* protects comp */
  48         int comp;
  49
  50         struct mutex read_lock; /* protects everything else */
  51
  52         int comp_irq;
  53         u32 comp_irq_trigger;
  54         u32 comp_irq_trigger_inv;
  55
  56         struct iio_channel *dac;
  57         struct delayed_work comp_timeout;
  58
  59         unsigned int comp_interval;
  60         bool invert;
  61         u32 dac_max;
  62
  63         int high;
  64         int level;
  65         int low;
  66
  67         struct completion done;
  68 };
  69
  70 /*
  71  * The envelope_detector_comp_latch function works together with the compare
  72  * interrupt service routine below (envelope_detector_comp_isr) as a latch
  73  * (one-bit memory) for if the interrupt has triggered since last calling
  74  * this function.
  75  * The ..._comp_isr function disables the interrupt so that the cpu does not
  76  * need to service a possible interrupt flood from the comparator when no-one
  77  * cares anyway, and this ..._comp_latch function reenables them again if
  78  * needed.
  79  */
  80 static int envelope_detector_comp_latch(struct envelope *env)
  81 {
  82         int comp;
  83
  84         spin_lock_irq(&env->comp_lock);
  85         comp = env->comp;
  86         env->comp = 0;
  87         spin_unlock_irq(&env->comp_lock);
  88
  89         if (!comp)
  90                 return 0;
  91
  92         /*
  93          * The irq was disabled, and is reenabled just now.
  94          * But there might have been a pending irq that
  95          * happened while the irq was disabled that fires
  96          * just as the irq is reenabled. That is not what
  97          * is desired.
  98          */
  99         enable_irq(env->comp_irq);
 100
 101         /* So, synchronize this possibly pending irq... */
 102         synchronize_irq(env->comp_irq);
 103
 104         /* ...and redo the whole dance. */
 105         spin_lock_irq(&env->comp_lock);
 106         comp = env->comp;
 107         env->comp = 0;
 108         spin_unlock_irq(&env->comp_lock);
 109
 110         if (comp)
 111                 enable_irq(env->comp_irq);
 112
 113         return 1;
 114 }
 115
 116 static irqreturn_t envelope_detector_comp_isr(int irq, void *ctx)
 117 {
 118         struct envelope *env = ctx;
 119
 120         spin_lock(&env->comp_lock);
 121         env->comp = 1;
 122         disable_irq_nosync(env->comp_irq);
 123         spin_unlock(&env->comp_lock);
 124
 125         return IRQ_HANDLED;
 126 }
 127
 128 static void envelope_detector_setup_compare(struct envelope *env)
 129 {
 130         int ret;
 131
 132         /*
 133          * Do a binary search for the peak input level, and stop
 134          * when that level is "trapped" between two adjacent DAC
 135          * values.
 136          * When invert is active, use the midpoint floor so that
 137          * env->level ends up as env->low when the termination
 138          * criteria below is fulfilled, and use the midpoint
 139          * ceiling when invert is not active so that env->level
 140          * ends up as env->high in that case.
 141          */
 142         env->level = (env->high + env->low + !env->invert) / 2;
 143
 144         if (env->high == env->low + 1) {
 145                 complete(&env->done);
 146                 return;
 147         }
 148
 149         /* Set a "safe" DAC level (if there is such a thing)... */
 150         ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);
 151         if (ret < 0)
 152                 goto err;
 153
 154         /* ...clear the comparison result... */
 155         envelope_detector_comp_latch(env);
 156
 157         /* ...set the real DAC level... */
 158         ret = iio_write_channel_raw(env->dac, env->level);
 159         if (ret < 0)
 160                 goto err;
 161
 162         /* ...and wait for a bit to see if the latch catches anything. */
 163         schedule_delayed_work(&env->comp_timeout,
 164                               msecs_to_jiffies(env->comp_interval));
 165         return;
 166
 167 err:
 168         env->level = ret;
 169         complete(&env->done);
 170 }
 171
 172 static void envelope_detector_timeout(struct work_struct *work)
 173 {
 174         struct envelope *env = container_of(work, struct envelope,
 175                                             comp_timeout.work);
 176
 177         /* Adjust low/high depending on the latch content... */
 178         if (!envelope_detector_comp_latch(env) ^ !env->invert)
 179                 env->low = env->level;
 180         else
 181                 env->high = env->level;
 182
 183         /* ...and continue the search. */
 184         envelope_detector_setup_compare(env);
 185 }
 186
 187 static int envelope_detector_read_raw(struct iio_dev *indio_dev,
 188                                       struct iio_chan_spec const *chan,
 189                                       int *val, int *val2, long mask)
 190 {
 191         struct envelope *env = iio_priv(indio_dev);
 192         int ret;
 193
 194         switch (mask) {
 195         case IIO_CHAN_INFO_RAW:
 196                 /*
 197                  * When invert is active, start with high=max+1 and low=0
 198                  * since we will end up with the low value when the
 199                  * termination criteria is fulfilled (rounding down). And
 200                  * start with high=max and low=-1 when invert is not active
 201                  * since we will end up with the high value in that case.
 202                  * This ensures that the returned value in both cases are
 203                  * in the same range as the DAC and is a value that has not
 204                  * triggered the comparator.
 205                  */
 206                 mutex_lock(&env->read_lock);
 207                 env->high = env->dac_max + env->invert;
 208                 env->low = -1 + env->invert;
 209                 envelope_detector_setup_compare(env);
 210                 wait_for_completion(&env->done);
 211                 if (env->level < 0) {
 212                         ret = env->level;
 213                         goto err_unlock;
 214                 }
 215                 *val = env->invert ? env->dac_max - env->level : env->level;
 216                 mutex_unlock(&env->read_lock);
 217
 218                 return IIO_VAL_INT;
 219
 220         case IIO_CHAN_INFO_SCALE:
 221                 return iio_read_channel_scale(env->dac, val, val2);
 222         }
 223
 224         return -EINVAL;
 225
 226 err_unlock:
 227         mutex_unlock(&env->read_lock);
 228         return ret;
 229 }
 230
 231 static ssize_t envelope_show_invert(struct iio_dev *indio_dev,
 232                                     uintptr_t private,
 233                                     struct iio_chan_spec const *ch, char *buf)
 234 {
 235         struct envelope *env = iio_priv(indio_dev);
 236
 237         return sprintf(buf, "%u\n", env->invert);
 238 }
 239
 240 static ssize_t envelope_store_invert(struct iio_dev *indio_dev,
 241                                      uintptr_t private,
 242                                      struct iio_chan_spec const *ch,
 243                                      const char *buf, size_t len)
 244 {
 245         struct envelope *env = iio_priv(indio_dev);
 246         unsigned long invert;
 247         int ret;
 248         u32 trigger;
 249
 250         ret = kstrtoul(buf, 0, &invert);
 251         if (ret < 0)
 252                 return ret;
 253         if (invert > 1)
 254                 return -EINVAL;
 255
 256         trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;
 257
 258         mutex_lock(&env->read_lock);
 259         if (invert != env->invert)
 260                 ret = irq_set_irq_type(env->comp_irq, trigger);
 261         if (!ret) {
 262                 env->invert = invert;
 263                 ret = len;
 264         }
 265         mutex_unlock(&env->read_lock);
 266
 267         return ret;
 268 }
 269
 270 static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,
 271                                            uintptr_t private,
 272                                            struct iio_chan_spec const *ch,
 273                                            char *buf)
 274 {
 275         struct envelope *env = iio_priv(indio_dev);
 276
 277         return sprintf(buf, "%u\n", env->comp_interval);
 278 }
 279
 280 static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,
 281                                             uintptr_t private,
 282                                             struct iio_chan_spec const *ch,
 283                                             const char *buf, size_t len)
 284 {
 285         struct envelope *env = iio_priv(indio_dev);
 286         unsigned long interval;
 287         int ret;
 288
 289         ret = kstrtoul(buf, 0, &interval);
 290         if (ret < 0)
 291                 return ret;
 292         if (interval > 1000)
 293                 return -EINVAL;
 294
 295         mutex_lock(&env->read_lock);
 296         env->comp_interval = interval;
 297         mutex_unlock(&env->read_lock);
 298
 299         return len;
 300 }
 301
 302 static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {
 303         { .name = "invert",
 304           .read = envelope_show_invert,
 305           .write = envelope_store_invert, },
 306         { .name = "compare_interval",
 307           .read = envelope_show_comp_interval,
 308           .write = envelope_store_comp_interval, },
 309         { /* sentinel */ }
 310 };
 311
 312 static const struct iio_chan_spec envelope_detector_iio_channel = {
 313         .type = IIO_ALTVOLTAGE,
 314         .info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
 315                             | BIT(IIO_CHAN_INFO_SCALE),
 316         .ext_info = envelope_detector_ext_info,
 317         .indexed = 1,
 318 };
 319
 320 static const struct iio_info envelope_detector_info = {
 321         .read_raw = &envelope_detector_read_raw,
 322 };
 323
 324 static int envelope_detector_probe(struct platform_device *pdev)
 325 {
 326         struct device *dev = &pdev->dev;
 327         struct iio_dev *indio_dev;
 328         struct envelope *env;
 329         enum iio_chan_type type;
 330         int ret;
 331
 332         indio_dev = devm_iio_device_alloc(dev, sizeof(*env));
 333         if (!indio_dev)
 334                 return -ENOMEM;
 335
 336         platform_set_drvdata(pdev, indio_dev);
 337         env = iio_priv(indio_dev);
 338         env->comp_interval = 50; /* some sensible default? */
 339
 340         spin_lock_init(&env->comp_lock);
 341         mutex_init(&env->read_lock);
 342         init_completion(&env->done);
 343         INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);
 344
 345         indio_dev->name = dev_name(dev);
 346         indio_dev->info = &envelope_detector_info;
 347         indio_dev->channels = &envelope_detector_iio_channel;
 348         indio_dev->num_channels = 1;
 349
 350         env->dac = devm_iio_channel_get(dev, "dac");
 351         if (IS_ERR(env->dac))
 352                 return dev_err_probe(dev, PTR_ERR(env->dac),
 353                                      "failed to get dac input channel\n");
 354
 355         env->comp_irq = platform_get_irq_byname(pdev, "comp");
 356         if (env->comp_irq < 0)
 357                 return env->comp_irq;
 358
 359         ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr,
 360                                0, "envelope-detector", env);
 361         if (ret)
 362                 return dev_err_probe(dev, ret, "failed to request interrupt\n");
 363
 364         env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);
 365         if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)
 366                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;
 367         if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)
 368                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;
 369         if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)
 370                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;
 371         if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)
 372                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;
 373
 374         ret = iio_get_channel_type(env->dac, &type);
 375         if (ret < 0)
 376                 return ret;
 377
 378         if (type != IIO_VOLTAGE) {
 379                 dev_err(dev, "dac is of the wrong type\n");
 380                 return -EINVAL;
 381         }
 382
 383         ret = iio_read_max_channel_raw(env->dac, &env->dac_max);
 384         if (ret < 0) {
 385                 dev_err(dev, "dac does not indicate its raw maximum value\n");
 386                 return ret;
 387         }
 388
 389         return devm_iio_device_register(dev, indio_dev);
 390 }
 391
 392 static const struct of_device_id envelope_detector_match[] = {
 393         { .compatible = "axentia,tse850-envelope-detector", },
 394         { /* sentinel */ }
 395 };
 396 MODULE_DEVICE_TABLE(of, envelope_detector_match);
 397
 398 static struct platform_driver envelope_detector_driver = {
 399         .probe = envelope_detector_probe,
 400         .driver = {
 401                 .name = "iio-envelope-detector",
 402                 .of_match_table = envelope_detector_match,
 403         },
 404 };
 405 module_platform_driver(envelope_detector_driver);
 406
 407 MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
 408 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
 409 MODULE_LICENSE("GPL v2");