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 */
envelope_detector_comp_latch(struct envelope * env)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
envelope_detector_comp_isr(int irq,void * ctx)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
envelope_detector_setup_compare(struct envelope * env)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
envelope_detector_timeout(struct work_struct * work)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
envelope_detector_read_raw(struct iio_dev * indio_dev,struct iio_chan_spec const * chan,int * val,int * val2,long mask)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
envelope_show_invert(struct iio_dev * indio_dev,uintptr_t private,struct iio_chan_spec const * ch,char * buf)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
envelope_store_invert(struct iio_dev * indio_dev,uintptr_t private,struct iio_chan_spec const * ch,const char * buf,size_t len)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
envelope_show_comp_interval(struct iio_dev * indio_dev,uintptr_t private,struct iio_chan_spec const * ch,char * buf)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
envelope_store_comp_interval(struct iio_dev * indio_dev,uintptr_t private,struct iio_chan_spec const * ch,const char * buf,size_t len)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
envelope_detector_probe(struct platform_device * pdev)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