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