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->dev.parent = dev; 347 indio_dev->dev.of_node = dev->of_node; 348 indio_dev->info = &envelope_detector_info; 349 indio_dev->channels = &envelope_detector_iio_channel; 350 indio_dev->num_channels = 1; 351 352 env->dac = devm_iio_channel_get(dev, "dac"); 353 if (IS_ERR(env->dac)) { 354 if (PTR_ERR(env->dac) != -EPROBE_DEFER) 355 dev_err(dev, "failed to get dac input channel\n"); 356 return PTR_ERR(env->dac); 357 } 358 359 env->comp_irq = platform_get_irq_byname(pdev, "comp"); 360 if (env->comp_irq < 0) { 361 if (env->comp_irq != -EPROBE_DEFER) 362 dev_err(dev, "failed to get compare interrupt\n"); 363 return env->comp_irq; 364 } 365 366 ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr, 367 0, "envelope-detector", env); 368 if (ret) { 369 if (ret != -EPROBE_DEFER) 370 dev_err(dev, "failed to request interrupt\n"); 371 return ret; 372 } 373 env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq); 374 if (env->comp_irq_trigger & IRQF_TRIGGER_RISING) 375 env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING; 376 if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING) 377 env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING; 378 if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH) 379 env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW; 380 if (env->comp_irq_trigger & IRQF_TRIGGER_LOW) 381 env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH; 382 383 ret = iio_get_channel_type(env->dac, &type); 384 if (ret < 0) 385 return ret; 386 387 if (type != IIO_VOLTAGE) { 388 dev_err(dev, "dac is of the wrong type\n"); 389 return -EINVAL; 390 } 391 392 ret = iio_read_max_channel_raw(env->dac, &env->dac_max); 393 if (ret < 0) { 394 dev_err(dev, "dac does not indicate its raw maximum value\n"); 395 return ret; 396 } 397 398 return devm_iio_device_register(dev, indio_dev); 399 } 400 401 static const struct of_device_id envelope_detector_match[] = { 402 { .compatible = "axentia,tse850-envelope-detector", }, 403 { /* sentinel */ } 404 }; 405 MODULE_DEVICE_TABLE(of, envelope_detector_match); 406 407 static struct platform_driver envelope_detector_driver = { 408 .probe = envelope_detector_probe, 409 .driver = { 410 .name = "iio-envelope-detector", 411 .of_match_table = envelope_detector_match, 412 }, 413 }; 414 module_platform_driver(envelope_detector_driver); 415 416 MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator"); 417 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>"); 418 MODULE_LICENSE("GPL v2"); 419