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