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
45struct 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 */
79static 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
115static 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
127static 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
166err:
167	env->level = ret;
168	complete(&env->done);
169}
170
171static 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
186static 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
225err_unlock:
226	mutex_unlock(&env->read_lock);
227	return ret;
228}
229
230static 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
239static 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
269static 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
279static 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
301static 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
311static 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
319static const struct iio_info envelope_detector_info = {
320	.read_raw = &envelope_detector_read_raw,
321};
322
323static 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
391static const struct of_device_id envelope_detector_match[] = {
392	{ .compatible = "axentia,tse850-envelope-detector", },
393	{ /* sentinel */ }
394};
395MODULE_DEVICE_TABLE(of, envelope_detector_match);
396
397static 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};
404module_platform_driver(envelope_detector_driver);
405
406MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
407MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
408MODULE_LICENSE("GPL v2");
409