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