drivers/iio/adc/envelope-detector.c

   1 /*
   2  * Driver for an envelope detector using a DAC and a comparator
   3  *
   4  * Copyright (C) 2016 Axentia Technologies AB
   5  *
   6  * Author: Peter Rosin <peda@axentia.se>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 /*
  14  * The DAC is used to find the peak level of an alternating voltage input
  15  * signal by a binary search using the output of a comparator wired to
  16  * an interrupt pin. Like so:
  17  *                           _
  18  *                          | \
  19  *     input +------>-------|+ \
  20  *                          |   \
  21  *            .-------.     |    }---.
  22  *            |       |     |   /    |
  23  *            |    dac|-->--|- /     |
  24  *            |       |     |_/      |
  25  *            |       |              |
  26  *            |       |              |
  27  *            |    irq|------<-------'
  28  *            |       |
  29  *            '-------'
  30  */
  31
  32 #include <linux/completion.h>
  33 #include <linux/device.h>
  34 #include <linux/err.h>
  35 #include <linux/kernel.h>
  36 #include <linux/module.h>
  37 #include <linux/mutex.h>
  38 #include <linux/iio/consumer.h>
  39 #include <linux/iio/iio.h>
  40 #include <linux/iio/sysfs.h>
  41 #include <linux/interrupt.h>
  42 #include <linux/irq.h>
  43 #include <linux/of.h>
  44 #include <linux/of_device.h>
  45 #include <linux/platform_device.h>
  46 #include <linux/spinlock.h>
  47 #include <linux/workqueue.h>
  48
  49 struct envelope {
  50         spinlock_t comp_lock; /* protects comp */
  51         int comp;
  52
  53         struct mutex read_lock; /* protects everything else */
  54
  55         int comp_irq;
  56         u32 comp_irq_trigger;
  57         u32 comp_irq_trigger_inv;
  58
  59         struct iio_channel *dac;
  60         struct delayed_work comp_timeout;
  61
  62         unsigned int comp_interval;
  63         bool invert;
  64         u32 dac_max;
  65
  66         int high;
  67         int level;
  68         int low;
  69
  70         struct completion done;
  71 };
  72
  73 /*
  74  * The envelope_detector_comp_latch function works together with the compare
  75  * interrupt service routine below (envelope_detector_comp_isr) as a latch
  76  * (one-bit memory) for if the interrupt has triggered since last calling
  77  * this function.
  78  * The ..._comp_isr function disables the interrupt so that the cpu does not
  79  * need to service a possible interrupt flood from the comparator when no-one
  80  * cares anyway, and this ..._comp_latch function reenables them again if
  81  * needed.
  82  */
  83 static int envelope_detector_comp_latch(struct envelope *env)
  84 {
  85         int comp;
  86
  87         spin_lock_irq(&env->comp_lock);
  88         comp = env->comp;
  89         env->comp = 0;
  90         spin_unlock_irq(&env->comp_lock);
  91
  92         if (!comp)
  93                 return 0;
  94
  95         /*
  96          * The irq was disabled, and is reenabled just now.
  97          * But there might have been a pending irq that
  98          * happened while the irq was disabled that fires
  99          * just as the irq is reenabled. That is not what
 100          * is desired.
 101          */
 102         enable_irq(env->comp_irq);
 103
 104         /* So, synchronize this possibly pending irq... */
 105         synchronize_irq(env->comp_irq);
 106
 107         /* ...and redo the whole dance. */
 108         spin_lock_irq(&env->comp_lock);
 109         comp = env->comp;
 110         env->comp = 0;
 111         spin_unlock_irq(&env->comp_lock);
 112
 113         if (comp)
 114                 enable_irq(env->comp_irq);
 115
 116         return 1;
 117 }
 118
 119 static irqreturn_t envelope_detector_comp_isr(int irq, void *ctx)
 120 {
 121         struct envelope *env = ctx;
 122
 123         spin_lock(&env->comp_lock);
 124         env->comp = 1;
 125         disable_irq_nosync(env->comp_irq);
 126         spin_unlock(&env->comp_lock);
 127
 128         return IRQ_HANDLED;
 129 }
 130
 131 static void envelope_detector_setup_compare(struct envelope *env)
 132 {
 133         int ret;
 134
 135         /*
 136          * Do a binary search for the peak input level, and stop
 137          * when that level is "trapped" between two adjacent DAC
 138          * values.
 139          * When invert is active, use the midpoint floor so that
 140          * env->level ends up as env->low when the termination
 141          * criteria below is fulfilled, and use the midpoint
 142          * ceiling when invert is not active so that env->level
 143          * ends up as env->high in that case.
 144          */
 145         env->level = (env->high + env->low + !env->invert) / 2;
 146
 147         if (env->high == env->low + 1) {
 148                 complete(&env->done);
 149                 return;
 150         }
 151
 152         /* Set a "safe" DAC level (if there is such a thing)... */
 153         ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);
 154         if (ret < 0)
 155                 goto err;
 156
 157         /* ...clear the comparison result... */
 158         envelope_detector_comp_latch(env);
 159
 160         /* ...set the real DAC level... */
 161         ret = iio_write_channel_raw(env->dac, env->level);
 162         if (ret < 0)
 163                 goto err;
 164
 165         /* ...and wait for a bit to see if the latch catches anything. */
 166         schedule_delayed_work(&env->comp_timeout,
 167                               msecs_to_jiffies(env->comp_interval));
 168         return;
 169
 170 err:
 171         env->level = ret;
 172         complete(&env->done);
 173 }
 174
 175 static void envelope_detector_timeout(struct work_struct *work)
 176 {
 177         struct envelope *env = container_of(work, struct envelope,
 178                                             comp_timeout.work);
 179
 180         /* Adjust low/high depending on the latch content... */
 181         if (!envelope_detector_comp_latch(env) ^ !env->invert)
 182                 env->low = env->level;
 183         else
 184                 env->high = env->level;
 185
 186         /* ...and continue the search. */
 187         envelope_detector_setup_compare(env);
 188 }
 189
 190 static int envelope_detector_read_raw(struct iio_dev *indio_dev,
 191                                       struct iio_chan_spec const *chan,
 192                                       int *val, int *val2, long mask)
 193 {
 194         struct envelope *env = iio_priv(indio_dev);
 195         int ret;
 196
 197         switch (mask) {
 198         case IIO_CHAN_INFO_RAW:
 199                 /*
 200                  * When invert is active, start with high=max+1 and low=0
 201                  * since we will end up with the low value when the
 202                  * termination criteria is fulfilled (rounding down). And
 203                  * start with high=max and low=-1 when invert is not active
 204                  * since we will end up with the high value in that case.
 205                  * This ensures that the returned value in both cases are
 206                  * in the same range as the DAC and is a value that has not
 207                  * triggered the comparator.
 208                  */
 209                 mutex_lock(&env->read_lock);
 210                 env->high = env->dac_max + env->invert;
 211                 env->low = -1 + env->invert;
 212                 envelope_detector_setup_compare(env);
 213                 wait_for_completion(&env->done);
 214                 if (env->level < 0) {
 215                         ret = env->level;
 216                         goto err_unlock;
 217                 }
 218                 *val = env->invert ? env->dac_max - env->level : env->level;
 219                 mutex_unlock(&env->read_lock);
 220
 221                 return IIO_VAL_INT;
 222
 223         case IIO_CHAN_INFO_SCALE:
 224                 return iio_read_channel_scale(env->dac, val, val2);
 225         }
 226
 227         return -EINVAL;
 228
 229 err_unlock:
 230         mutex_unlock(&env->read_lock);
 231         return ret;
 232 }
 233
 234 static ssize_t envelope_show_invert(struct iio_dev *indio_dev,
 235                                     uintptr_t private,
 236                                     struct iio_chan_spec const *ch, char *buf)
 237 {
 238         struct envelope *env = iio_priv(indio_dev);
 239
 240         return sprintf(buf, "%u\n", env->invert);
 241 }
 242
 243 static ssize_t envelope_store_invert(struct iio_dev *indio_dev,
 244                                      uintptr_t private,
 245                                      struct iio_chan_spec const *ch,
 246                                      const char *buf, size_t len)
 247 {
 248         struct envelope *env = iio_priv(indio_dev);
 249         unsigned long invert;
 250         int ret;
 251         u32 trigger;
 252
 253         ret = kstrtoul(buf, 0, &invert);
 254         if (ret < 0)
 255                 return ret;
 256         if (invert > 1)
 257                 return -EINVAL;
 258
 259         trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;
 260
 261         mutex_lock(&env->read_lock);
 262         if (invert != env->invert)
 263                 ret = irq_set_irq_type(env->comp_irq, trigger);
 264         if (!ret) {
 265                 env->invert = invert;
 266                 ret = len;
 267         }
 268         mutex_unlock(&env->read_lock);
 269
 270         return ret;
 271 }
 272
 273 static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,
 274                                            uintptr_t private,
 275                                            struct iio_chan_spec const *ch,
 276                                            char *buf)
 277 {
 278         struct envelope *env = iio_priv(indio_dev);
 279
 280         return sprintf(buf, "%u\n", env->comp_interval);
 281 }
 282
 283 static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,
 284                                             uintptr_t private,
 285                                             struct iio_chan_spec const *ch,
 286                                             const char *buf, size_t len)
 287 {
 288         struct envelope *env = iio_priv(indio_dev);
 289         unsigned long interval;
 290         int ret;
 291
 292         ret = kstrtoul(buf, 0, &interval);
 293         if (ret < 0)
 294                 return ret;
 295         if (interval > 1000)
 296                 return -EINVAL;
 297
 298         mutex_lock(&env->read_lock);
 299         env->comp_interval = interval;
 300         mutex_unlock(&env->read_lock);
 301
 302         return len;
 303 }
 304
 305 static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {
 306         { .name = "invert",
 307           .read = envelope_show_invert,
 308           .write = envelope_store_invert, },
 309         { .name = "compare_interval",
 310           .read = envelope_show_comp_interval,
 311           .write = envelope_store_comp_interval, },
 312         { /* sentinel */ }
 313 };
 314
 315 static const struct iio_chan_spec envelope_detector_iio_channel = {
 316         .type = IIO_ALTVOLTAGE,
 317         .info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
 318                             | BIT(IIO_CHAN_INFO_SCALE),
 319         .ext_info = envelope_detector_ext_info,
 320         .indexed = 1,
 321 };
 322
 323 static const struct iio_info envelope_detector_info = {
 324         .read_raw = &envelope_detector_read_raw,
 325         .driver_module = THIS_MODULE,
 326 };
 327
 328 static int envelope_detector_probe(struct platform_device *pdev)
 329 {
 330         struct device *dev = &pdev->dev;
 331         struct iio_dev *indio_dev;
 332         struct envelope *env;
 333         enum iio_chan_type type;
 334         int ret;
 335
 336         indio_dev = devm_iio_device_alloc(dev, sizeof(*env));
 337         if (!indio_dev)
 338                 return -ENOMEM;
 339
 340         platform_set_drvdata(pdev, indio_dev);
 341         env = iio_priv(indio_dev);
 342         env->comp_interval = 50; /* some sensible default? */
 343
 344         spin_lock_init(&env->comp_lock);
 345         mutex_init(&env->read_lock);
 346         init_completion(&env->done);
 347         INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);
 348
 349         indio_dev->name = dev_name(dev);
 350         indio_dev->dev.parent = dev;
 351         indio_dev->dev.of_node = dev->of_node;
 352         indio_dev->info = &envelope_detector_info;
 353         indio_dev->channels = &envelope_detector_iio_channel;
 354         indio_dev->num_channels = 1;
 355
 356         env->dac = devm_iio_channel_get(dev, "dac");
 357         if (IS_ERR(env->dac)) {
 358                 if (PTR_ERR(env->dac) != -EPROBE_DEFER)
 359                         dev_err(dev, "failed to get dac input channel\n");
 360                 return PTR_ERR(env->dac);
 361         }
 362
 363         env->comp_irq = platform_get_irq_byname(pdev, "comp");
 364         if (env->comp_irq < 0) {
 365                 if (env->comp_irq != -EPROBE_DEFER)
 366                         dev_err(dev, "failed to get compare interrupt\n");
 367                 return env->comp_irq;
 368         }
 369
 370         ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr,
 371                                0, "envelope-detector", env);
 372         if (ret) {
 373                 if (ret != -EPROBE_DEFER)
 374                         dev_err(dev, "failed to request interrupt\n");
 375                 return ret;
 376         }
 377         env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);
 378         if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)
 379                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;
 380         if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)
 381                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;
 382         if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)
 383                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;
 384         if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)
 385                 env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;
 386
 387         ret = iio_get_channel_type(env->dac, &type);
 388         if (ret < 0)
 389                 return ret;
 390
 391         if (type != IIO_VOLTAGE) {
 392                 dev_err(dev, "dac is of the wrong type\n");
 393                 return -EINVAL;
 394         }
 395
 396         ret = iio_read_max_channel_raw(env->dac, &env->dac_max);
 397         if (ret < 0) {
 398                 dev_err(dev, "dac does not indicate its raw maximum value\n");
 399                 return ret;
 400         }
 401
 402         return devm_iio_device_register(dev, indio_dev);
 403 }
 404
 405 static const struct of_device_id envelope_detector_match[] = {
 406         { .compatible = "axentia,tse850-envelope-detector", },
 407         { /* sentinel */ }
 408 };
 409 MODULE_DEVICE_TABLE(of, envelope_detector_match);
 410
 411 static struct platform_driver envelope_detector_driver = {
 412         .probe = envelope_detector_probe,
 413         .driver = {
 414                 .name = "iio-envelope-detector",
 415                 .of_match_table = envelope_detector_match,
 416         },
 417 };
 418 module_platform_driver(envelope_detector_driver);
 419
 420 MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
 421 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
 422 MODULE_LICENSE("GPL v2");