xref: /openbmc/linux/drivers/iio/afe/iio-rescale.c (revision f5c27da4)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * IIO rescale driver
4  *
5  * Copyright (C) 2018 Axentia Technologies AB
6  * Copyright (C) 2022 Liam Beguin <liambeguin@gmail.com>
7  *
8  * Author: Peter Rosin <peda@axentia.se>
9  */
10 
11 #include <linux/err.h>
12 #include <linux/gcd.h>
13 #include <linux/mod_devicetable.h>
14 #include <linux/module.h>
15 #include <linux/platform_device.h>
16 #include <linux/property.h>
17 
18 #include <linux/iio/afe/rescale.h>
19 #include <linux/iio/consumer.h>
20 #include <linux/iio/iio.h>
21 
22 int rescale_process_scale(struct rescale *rescale, int scale_type,
23 			  int *val, int *val2)
24 {
25 	s64 tmp;
26 	int _val, _val2;
27 	s32 rem, rem2;
28 	u32 mult;
29 	u32 neg;
30 
31 	switch (scale_type) {
32 	case IIO_VAL_INT:
33 		*val *= rescale->numerator;
34 		if (rescale->denominator == 1)
35 			return scale_type;
36 		*val2 = rescale->denominator;
37 		return IIO_VAL_FRACTIONAL;
38 	case IIO_VAL_FRACTIONAL:
39 		/*
40 		 * When the product of both scales doesn't overflow, avoid
41 		 * potential accuracy loss (for in kernel consumers) by
42 		 * keeping a fractional representation.
43 		 */
44 		if (!check_mul_overflow(*val, rescale->numerator, &_val) &&
45 		    !check_mul_overflow(*val2, rescale->denominator, &_val2)) {
46 			*val = _val;
47 			*val2 = _val2;
48 			return IIO_VAL_FRACTIONAL;
49 		}
50 		fallthrough;
51 	case IIO_VAL_FRACTIONAL_LOG2:
52 		tmp = (s64)*val * 1000000000LL;
53 		tmp = div_s64(tmp, rescale->denominator);
54 		tmp *= rescale->numerator;
55 
56 		tmp = div_s64_rem(tmp, 1000000000LL, &rem);
57 		*val = tmp;
58 
59 		if (!rem)
60 			return scale_type;
61 
62 		if (scale_type == IIO_VAL_FRACTIONAL)
63 			tmp = *val2;
64 		else
65 			tmp = ULL(1) << *val2;
66 
67 		rem2 = *val % (int)tmp;
68 		*val = *val / (int)tmp;
69 
70 		*val2 = rem / (int)tmp;
71 		if (rem2)
72 			*val2 += div_s64((s64)rem2 * 1000000000LL, tmp);
73 
74 		return IIO_VAL_INT_PLUS_NANO;
75 	case IIO_VAL_INT_PLUS_NANO:
76 	case IIO_VAL_INT_PLUS_MICRO:
77 		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? 1000000000L : 1000000L;
78 
79 		/*
80 		 * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if either *val
81 		 * OR *val2 is negative the schan scale is negative, i.e.
82 		 * *val = 1 and *val2 = -0.5 yields -1.5 not -0.5.
83 		 */
84 		neg = *val < 0 || *val2 < 0;
85 
86 		tmp = (s64)abs(*val) * abs(rescale->numerator);
87 		*val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
88 
89 		tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
90 		tmp = div_s64(tmp, abs(rescale->denominator));
91 
92 		*val += div_s64_rem(tmp, mult, val2);
93 
94 		/*
95 		 * If only one of the rescaler elements or the schan scale is
96 		 * negative, the combined scale is negative.
97 		 */
98 		if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
99 			if (*val)
100 				*val = -*val;
101 			else
102 				*val2 = -*val2;
103 		}
104 
105 		return scale_type;
106 	default:
107 		return -EOPNOTSUPP;
108 	}
109 }
110 EXPORT_SYMBOL_NS_GPL(rescale_process_scale, IIO_RESCALE);
111 
112 int rescale_process_offset(struct rescale *rescale, int scale_type,
113 			   int scale, int scale2, int schan_off,
114 			   int *val, int *val2)
115 {
116 	s64 tmp, tmp2;
117 
118 	switch (scale_type) {
119 	case IIO_VAL_FRACTIONAL:
120 		tmp = (s64)rescale->offset * scale2;
121 		*val = div_s64(tmp, scale) + schan_off;
122 		return IIO_VAL_INT;
123 	case IIO_VAL_INT:
124 		*val = div_s64(rescale->offset, scale) + schan_off;
125 		return IIO_VAL_INT;
126 	case IIO_VAL_FRACTIONAL_LOG2:
127 		tmp = (s64)rescale->offset * (1 << scale2);
128 		*val = div_s64(tmp, scale) + schan_off;
129 		return IIO_VAL_INT;
130 	case IIO_VAL_INT_PLUS_NANO:
131 		tmp = (s64)rescale->offset * 1000000000LL;
132 		tmp2 = ((s64)scale * 1000000000LL) + scale2;
133 		*val = div64_s64(tmp, tmp2) + schan_off;
134 		return IIO_VAL_INT;
135 	case IIO_VAL_INT_PLUS_MICRO:
136 		tmp = (s64)rescale->offset * 1000000LL;
137 		tmp2 = ((s64)scale * 1000000LL) + scale2;
138 		*val = div64_s64(tmp, tmp2) + schan_off;
139 		return IIO_VAL_INT;
140 	default:
141 		return -EOPNOTSUPP;
142 	}
143 }
144 EXPORT_SYMBOL_NS_GPL(rescale_process_offset, IIO_RESCALE);
145 
146 static int rescale_read_raw(struct iio_dev *indio_dev,
147 			    struct iio_chan_spec const *chan,
148 			    int *val, int *val2, long mask)
149 {
150 	struct rescale *rescale = iio_priv(indio_dev);
151 	int scale, scale2;
152 	int schan_off = 0;
153 	int ret;
154 
155 	switch (mask) {
156 	case IIO_CHAN_INFO_RAW:
157 		if (rescale->chan_processed)
158 			/*
159 			 * When only processed channels are supported, we
160 			 * read the processed data and scale it by 1/1
161 			 * augmented with whatever the rescaler has calculated.
162 			 */
163 			return iio_read_channel_processed(rescale->source, val);
164 		else
165 			return iio_read_channel_raw(rescale->source, val);
166 
167 	case IIO_CHAN_INFO_SCALE:
168 		if (rescale->chan_processed) {
169 			/*
170 			 * Processed channels are scaled 1-to-1
171 			 */
172 			*val = 1;
173 			*val2 = 1;
174 			ret = IIO_VAL_FRACTIONAL;
175 		} else {
176 			ret = iio_read_channel_scale(rescale->source, val, val2);
177 		}
178 		return rescale_process_scale(rescale, ret, val, val2);
179 	case IIO_CHAN_INFO_OFFSET:
180 		/*
181 		 * Processed channels are scaled 1-to-1 and source offset is
182 		 * already taken into account.
183 		 *
184 		 * In other cases, real world measurement are expressed as:
185 		 *
186 		 *	schan_scale * (raw + schan_offset)
187 		 *
188 		 * Given that the rescaler parameters are applied recursively:
189 		 *
190 		 *	rescaler_scale * (schan_scale * (raw + schan_offset) +
191 		 *		rescaler_offset)
192 		 *
193 		 * Or,
194 		 *
195 		 *	(rescaler_scale * schan_scale) * (raw +
196 		 *		(schan_offset +	rescaler_offset / schan_scale)
197 		 *
198 		 * Thus, reusing the original expression the parameters exposed
199 		 * to userspace are:
200 		 *
201 		 *	scale = schan_scale * rescaler_scale
202 		 *	offset = schan_offset + rescaler_offset / schan_scale
203 		 */
204 		if (rescale->chan_processed) {
205 			*val = rescale->offset;
206 			return IIO_VAL_INT;
207 		}
208 
209 		if (iio_channel_has_info(rescale->source->channel,
210 					 IIO_CHAN_INFO_OFFSET)) {
211 			ret = iio_read_channel_offset(rescale->source,
212 						      &schan_off, NULL);
213 			if (ret != IIO_VAL_INT)
214 				return ret < 0 ? ret : -EOPNOTSUPP;
215 		}
216 
217 		ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
218 		return rescale_process_offset(rescale, ret, scale, scale2,
219 					      schan_off, val, val2);
220 	default:
221 		return -EINVAL;
222 	}
223 }
224 
225 static int rescale_read_avail(struct iio_dev *indio_dev,
226 			      struct iio_chan_spec const *chan,
227 			      const int **vals, int *type, int *length,
228 			      long mask)
229 {
230 	struct rescale *rescale = iio_priv(indio_dev);
231 
232 	switch (mask) {
233 	case IIO_CHAN_INFO_RAW:
234 		*type = IIO_VAL_INT;
235 		return iio_read_avail_channel_raw(rescale->source,
236 						  vals, length);
237 	default:
238 		return -EINVAL;
239 	}
240 }
241 
242 static const struct iio_info rescale_info = {
243 	.read_raw = rescale_read_raw,
244 	.read_avail = rescale_read_avail,
245 };
246 
247 static ssize_t rescale_read_ext_info(struct iio_dev *indio_dev,
248 				     uintptr_t private,
249 				     struct iio_chan_spec const *chan,
250 				     char *buf)
251 {
252 	struct rescale *rescale = iio_priv(indio_dev);
253 
254 	return iio_read_channel_ext_info(rescale->source,
255 					 rescale->ext_info[private].name,
256 					 buf);
257 }
258 
259 static ssize_t rescale_write_ext_info(struct iio_dev *indio_dev,
260 				      uintptr_t private,
261 				      struct iio_chan_spec const *chan,
262 				      const char *buf, size_t len)
263 {
264 	struct rescale *rescale = iio_priv(indio_dev);
265 
266 	return iio_write_channel_ext_info(rescale->source,
267 					  rescale->ext_info[private].name,
268 					  buf, len);
269 }
270 
271 static int rescale_configure_channel(struct device *dev,
272 				     struct rescale *rescale)
273 {
274 	struct iio_chan_spec *chan = &rescale->chan;
275 	struct iio_chan_spec const *schan = rescale->source->channel;
276 
277 	chan->indexed = 1;
278 	chan->output = schan->output;
279 	chan->ext_info = rescale->ext_info;
280 	chan->type = rescale->cfg->type;
281 
282 	if (iio_channel_has_info(schan, IIO_CHAN_INFO_RAW) &&
283 	    iio_channel_has_info(schan, IIO_CHAN_INFO_SCALE)) {
284 		dev_info(dev, "using raw+scale source channel\n");
285 	} else if (iio_channel_has_info(schan, IIO_CHAN_INFO_PROCESSED)) {
286 		dev_info(dev, "using processed channel\n");
287 		rescale->chan_processed = true;
288 	} else {
289 		dev_err(dev, "source channel is not supported\n");
290 		return -EINVAL;
291 	}
292 
293 	chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
294 		BIT(IIO_CHAN_INFO_SCALE);
295 
296 	if (rescale->offset)
297 		chan->info_mask_separate |= BIT(IIO_CHAN_INFO_OFFSET);
298 
299 	/*
300 	 * Using .read_avail() is fringe to begin with and makes no sense
301 	 * whatsoever for processed channels, so we make sure that this cannot
302 	 * be called on a processed channel.
303 	 */
304 	if (iio_channel_has_available(schan, IIO_CHAN_INFO_RAW) &&
305 	    !rescale->chan_processed)
306 		chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
307 
308 	return 0;
309 }
310 
311 static int rescale_current_sense_amplifier_props(struct device *dev,
312 						 struct rescale *rescale)
313 {
314 	u32 sense;
315 	u32 gain_mult = 1;
316 	u32 gain_div = 1;
317 	u32 factor;
318 	int ret;
319 
320 	ret = device_property_read_u32(dev, "sense-resistor-micro-ohms",
321 				       &sense);
322 	if (ret) {
323 		dev_err(dev, "failed to read the sense resistance: %d\n", ret);
324 		return ret;
325 	}
326 
327 	device_property_read_u32(dev, "sense-gain-mult", &gain_mult);
328 	device_property_read_u32(dev, "sense-gain-div", &gain_div);
329 
330 	/*
331 	 * Calculate the scaling factor, 1 / (gain * sense), or
332 	 * gain_div / (gain_mult * sense), while trying to keep the
333 	 * numerator/denominator from overflowing.
334 	 */
335 	factor = gcd(sense, 1000000);
336 	rescale->numerator = 1000000 / factor;
337 	rescale->denominator = sense / factor;
338 
339 	factor = gcd(rescale->numerator, gain_mult);
340 	rescale->numerator /= factor;
341 	rescale->denominator *= gain_mult / factor;
342 
343 	factor = gcd(rescale->denominator, gain_div);
344 	rescale->numerator *= gain_div / factor;
345 	rescale->denominator /= factor;
346 
347 	return 0;
348 }
349 
350 static int rescale_current_sense_shunt_props(struct device *dev,
351 					     struct rescale *rescale)
352 {
353 	u32 shunt;
354 	u32 factor;
355 	int ret;
356 
357 	ret = device_property_read_u32(dev, "shunt-resistor-micro-ohms",
358 				       &shunt);
359 	if (ret) {
360 		dev_err(dev, "failed to read the shunt resistance: %d\n", ret);
361 		return ret;
362 	}
363 
364 	factor = gcd(shunt, 1000000);
365 	rescale->numerator = 1000000 / factor;
366 	rescale->denominator = shunt / factor;
367 
368 	return 0;
369 }
370 
371 static int rescale_voltage_divider_props(struct device *dev,
372 					 struct rescale *rescale)
373 {
374 	int ret;
375 	u32 factor;
376 
377 	ret = device_property_read_u32(dev, "output-ohms",
378 				       &rescale->denominator);
379 	if (ret) {
380 		dev_err(dev, "failed to read output-ohms: %d\n", ret);
381 		return ret;
382 	}
383 
384 	ret = device_property_read_u32(dev, "full-ohms",
385 				       &rescale->numerator);
386 	if (ret) {
387 		dev_err(dev, "failed to read full-ohms: %d\n", ret);
388 		return ret;
389 	}
390 
391 	factor = gcd(rescale->numerator, rescale->denominator);
392 	rescale->numerator /= factor;
393 	rescale->denominator /= factor;
394 
395 	return 0;
396 }
397 
398 static int rescale_temp_sense_rtd_props(struct device *dev,
399 					struct rescale *rescale)
400 {
401 	u32 factor;
402 	u32 alpha;
403 	u32 iexc;
404 	u32 tmp;
405 	int ret;
406 	u32 r0;
407 
408 	ret = device_property_read_u32(dev, "excitation-current-microamp",
409 				       &iexc);
410 	if (ret) {
411 		dev_err(dev, "failed to read excitation-current-microamp: %d\n",
412 			ret);
413 		return ret;
414 	}
415 
416 	ret = device_property_read_u32(dev, "alpha-ppm-per-celsius", &alpha);
417 	if (ret) {
418 		dev_err(dev, "failed to read alpha-ppm-per-celsius: %d\n",
419 			ret);
420 		return ret;
421 	}
422 
423 	ret = device_property_read_u32(dev, "r-naught-ohms", &r0);
424 	if (ret) {
425 		dev_err(dev, "failed to read r-naught-ohms: %d\n", ret);
426 		return ret;
427 	}
428 
429 	tmp = r0 * iexc * alpha / 1000000;
430 	factor = gcd(tmp, 1000000);
431 	rescale->numerator = 1000000 / factor;
432 	rescale->denominator = tmp / factor;
433 
434 	rescale->offset = -1 * ((r0 * iexc) / 1000);
435 
436 	return 0;
437 }
438 
439 static int rescale_temp_transducer_props(struct device *dev,
440 					 struct rescale *rescale)
441 {
442 	s32 offset = 0;
443 	s32 sense = 1;
444 	s32 alpha;
445 	int ret;
446 
447 	device_property_read_u32(dev, "sense-offset-millicelsius", &offset);
448 	device_property_read_u32(dev, "sense-resistor-ohms", &sense);
449 	ret = device_property_read_u32(dev, "alpha-ppm-per-celsius", &alpha);
450 	if (ret) {
451 		dev_err(dev, "failed to read alpha-ppm-per-celsius: %d\n", ret);
452 		return ret;
453 	}
454 
455 	rescale->numerator = 1000000;
456 	rescale->denominator = alpha * sense;
457 
458 	rescale->offset = div_s64((s64)offset * rescale->denominator,
459 				  rescale->numerator);
460 
461 	return 0;
462 }
463 
464 enum rescale_variant {
465 	CURRENT_SENSE_AMPLIFIER,
466 	CURRENT_SENSE_SHUNT,
467 	VOLTAGE_DIVIDER,
468 	TEMP_SENSE_RTD,
469 	TEMP_TRANSDUCER,
470 };
471 
472 static const struct rescale_cfg rescale_cfg[] = {
473 	[CURRENT_SENSE_AMPLIFIER] = {
474 		.type = IIO_CURRENT,
475 		.props = rescale_current_sense_amplifier_props,
476 	},
477 	[CURRENT_SENSE_SHUNT] = {
478 		.type = IIO_CURRENT,
479 		.props = rescale_current_sense_shunt_props,
480 	},
481 	[VOLTAGE_DIVIDER] = {
482 		.type = IIO_VOLTAGE,
483 		.props = rescale_voltage_divider_props,
484 	},
485 	[TEMP_SENSE_RTD] = {
486 		.type = IIO_TEMP,
487 		.props = rescale_temp_sense_rtd_props,
488 	},
489 	[TEMP_TRANSDUCER] = {
490 		.type = IIO_TEMP,
491 		.props = rescale_temp_transducer_props,
492 	},
493 };
494 
495 static const struct of_device_id rescale_match[] = {
496 	{ .compatible = "current-sense-amplifier",
497 	  .data = &rescale_cfg[CURRENT_SENSE_AMPLIFIER], },
498 	{ .compatible = "current-sense-shunt",
499 	  .data = &rescale_cfg[CURRENT_SENSE_SHUNT], },
500 	{ .compatible = "voltage-divider",
501 	  .data = &rescale_cfg[VOLTAGE_DIVIDER], },
502 	{ .compatible = "temperature-sense-rtd",
503 	  .data = &rescale_cfg[TEMP_SENSE_RTD], },
504 	{ .compatible = "temperature-transducer",
505 	  .data = &rescale_cfg[TEMP_TRANSDUCER], },
506 	{ /* sentinel */ }
507 };
508 MODULE_DEVICE_TABLE(of, rescale_match);
509 
510 static int rescale_probe(struct platform_device *pdev)
511 {
512 	struct device *dev = &pdev->dev;
513 	struct iio_dev *indio_dev;
514 	struct iio_channel *source;
515 	struct rescale *rescale;
516 	int sizeof_ext_info;
517 	int sizeof_priv;
518 	int i;
519 	int ret;
520 
521 	source = devm_iio_channel_get(dev, NULL);
522 	if (IS_ERR(source))
523 		return dev_err_probe(dev, PTR_ERR(source),
524 				     "failed to get source channel\n");
525 
526 	sizeof_ext_info = iio_get_channel_ext_info_count(source);
527 	if (sizeof_ext_info) {
528 		sizeof_ext_info += 1; /* one extra entry for the sentinel */
529 		sizeof_ext_info *= sizeof(*rescale->ext_info);
530 	}
531 
532 	sizeof_priv = sizeof(*rescale) + sizeof_ext_info;
533 
534 	indio_dev = devm_iio_device_alloc(dev, sizeof_priv);
535 	if (!indio_dev)
536 		return -ENOMEM;
537 
538 	rescale = iio_priv(indio_dev);
539 
540 	rescale->cfg = device_get_match_data(dev);
541 	rescale->numerator = 1;
542 	rescale->denominator = 1;
543 	rescale->offset = 0;
544 
545 	ret = rescale->cfg->props(dev, rescale);
546 	if (ret)
547 		return ret;
548 
549 	if (!rescale->numerator || !rescale->denominator) {
550 		dev_err(dev, "invalid scaling factor.\n");
551 		return -EINVAL;
552 	}
553 
554 	platform_set_drvdata(pdev, indio_dev);
555 
556 	rescale->source = source;
557 
558 	indio_dev->name = dev_name(dev);
559 	indio_dev->info = &rescale_info;
560 	indio_dev->modes = INDIO_DIRECT_MODE;
561 	indio_dev->channels = &rescale->chan;
562 	indio_dev->num_channels = 1;
563 	if (sizeof_ext_info) {
564 		rescale->ext_info = devm_kmemdup(dev,
565 						 source->channel->ext_info,
566 						 sizeof_ext_info, GFP_KERNEL);
567 		if (!rescale->ext_info)
568 			return -ENOMEM;
569 
570 		for (i = 0; rescale->ext_info[i].name; ++i) {
571 			struct iio_chan_spec_ext_info *ext_info =
572 				&rescale->ext_info[i];
573 
574 			if (source->channel->ext_info[i].read)
575 				ext_info->read = rescale_read_ext_info;
576 			if (source->channel->ext_info[i].write)
577 				ext_info->write = rescale_write_ext_info;
578 			ext_info->private = i;
579 		}
580 	}
581 
582 	ret = rescale_configure_channel(dev, rescale);
583 	if (ret)
584 		return ret;
585 
586 	return devm_iio_device_register(dev, indio_dev);
587 }
588 
589 static struct platform_driver rescale_driver = {
590 	.probe = rescale_probe,
591 	.driver = {
592 		.name = "iio-rescale",
593 		.of_match_table = rescale_match,
594 	},
595 };
596 module_platform_driver(rescale_driver);
597 
598 MODULE_DESCRIPTION("IIO rescale driver");
599 MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
600 MODULE_LICENSE("GPL v2");
601