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 }; 326 327 static int envelope_detector_probe(struct platform_device *pdev) 328 { 329 struct device *dev = &pdev->dev; 330 struct iio_dev *indio_dev; 331 struct envelope *env; 332 enum iio_chan_type type; 333 int ret; 334 335 indio_dev = devm_iio_device_alloc(dev, sizeof(*env)); 336 if (!indio_dev) 337 return -ENOMEM; 338 339 platform_set_drvdata(pdev, indio_dev); 340 env = iio_priv(indio_dev); 341 env->comp_interval = 50; /* some sensible default? */ 342 343 spin_lock_init(&env->comp_lock); 344 mutex_init(&env->read_lock); 345 init_completion(&env->done); 346 INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout); 347 348 indio_dev->name = dev_name(dev); 349 indio_dev->dev.parent = dev; 350 indio_dev->dev.of_node = dev->of_node; 351 indio_dev->info = &envelope_detector_info; 352 indio_dev->channels = &envelope_detector_iio_channel; 353 indio_dev->num_channels = 1; 354 355 env->dac = devm_iio_channel_get(dev, "dac"); 356 if (IS_ERR(env->dac)) { 357 if (PTR_ERR(env->dac) != -EPROBE_DEFER) 358 dev_err(dev, "failed to get dac input channel\n"); 359 return PTR_ERR(env->dac); 360 } 361 362 env->comp_irq = platform_get_irq_byname(pdev, "comp"); 363 if (env->comp_irq < 0) { 364 if (env->comp_irq != -EPROBE_DEFER) 365 dev_err(dev, "failed to get compare interrupt\n"); 366 return env->comp_irq; 367 } 368 369 ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr, 370 0, "envelope-detector", env); 371 if (ret) { 372 if (ret != -EPROBE_DEFER) 373 dev_err(dev, "failed to request interrupt\n"); 374 return ret; 375 } 376 env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq); 377 if (env->comp_irq_trigger & IRQF_TRIGGER_RISING) 378 env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING; 379 if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING) 380 env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING; 381 if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH) 382 env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW; 383 if (env->comp_irq_trigger & IRQF_TRIGGER_LOW) 384 env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH; 385 386 ret = iio_get_channel_type(env->dac, &type); 387 if (ret < 0) 388 return ret; 389 390 if (type != IIO_VOLTAGE) { 391 dev_err(dev, "dac is of the wrong type\n"); 392 return -EINVAL; 393 } 394 395 ret = iio_read_max_channel_raw(env->dac, &env->dac_max); 396 if (ret < 0) { 397 dev_err(dev, "dac does not indicate its raw maximum value\n"); 398 return ret; 399 } 400 401 return devm_iio_device_register(dev, indio_dev); 402 } 403 404 static const struct of_device_id envelope_detector_match[] = { 405 { .compatible = "axentia,tse850-envelope-detector", }, 406 { /* sentinel */ } 407 }; 408 MODULE_DEVICE_TABLE(of, envelope_detector_match); 409 410 static struct platform_driver envelope_detector_driver = { 411 .probe = envelope_detector_probe, 412 .driver = { 413 .name = "iio-envelope-detector", 414 .of_match_table = envelope_detector_match, 415 }, 416 }; 417 module_platform_driver(envelope_detector_driver); 418 419 MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator"); 420 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>"); 421 MODULE_LICENSE("GPL v2"); 422