summaryrefslogtreecommitdiffstats
path: root/kernel/drivers/gpio/gpiolib-sysfs.c
blob: af3bc7a8033bdcbaa2e93602bb107fbe12968d35 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/device.h>
#include <linux/sysfs.h>
#include <linux/gpio/consumer.h>
#include <linux/gpio/driver.h>
#include <linux/interrupt.h>
#include <linux/kdev_t.h>

#include "gpiolib.h"

static DEFINE_IDR(dirent_idr);


/* lock protects against unexport_gpio() being called while
 * sysfs files are active.
 */
static DEFINE_MUTEX(sysfs_lock);

/*
 * /sys/class/gpio/gpioN... only for GPIOs that are exported
 *   /direction
 *      * MAY BE OMITTED if kernel won't allow direction changes
 *      * is read/write as "in" or "out"
 *      * may also be written as "high" or "low", initializing
 *        output value as specified ("out" implies "low")
 *   /value
 *      * always readable, subject to hardware behavior
 *      * may be writable, as zero/nonzero
 *   /edge
 *      * configures behavior of poll(2) on /value
 *      * available only if pin can generate IRQs on input
 *      * is read/write as "none", "falling", "rising", or "both"
 *   /active_low
 *      * configures polarity of /value
 *      * is read/write as zero/nonzero
 *      * also affects existing and subsequent "falling" and "rising"
 *        /edge configuration
 */

static ssize_t gpio_direction_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags)) {
		status = -EIO;
	} else {
		gpiod_get_direction(desc);
		status = sprintf(buf, "%s\n",
			test_bit(FLAG_IS_OUT, &desc->flags)
				? "out" : "in");
	}

	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_direction_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else if (sysfs_streq(buf, "high"))
		status = gpiod_direction_output_raw(desc, 1);
	else if (sysfs_streq(buf, "out") || sysfs_streq(buf, "low"))
		status = gpiod_direction_output_raw(desc, 0);
	else if (sysfs_streq(buf, "in"))
		status = gpiod_direction_input(desc);
	else
		status = -EINVAL;

	mutex_unlock(&sysfs_lock);
	return status ? : size;
}

static /* const */ DEVICE_ATTR(direction, 0644,
		gpio_direction_show, gpio_direction_store);

static ssize_t gpio_value_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else
		status = sprintf(buf, "%d\n", gpiod_get_value_cansleep(desc));

	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_value_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else if (!test_bit(FLAG_IS_OUT, &desc->flags))
		status = -EPERM;
	else {
		long		value;

		status = kstrtol(buf, 0, &value);
		if (status == 0) {
			gpiod_set_value_cansleep(desc, value);
			status = size;
		}
	}

	mutex_unlock(&sysfs_lock);
	return status;
}

static DEVICE_ATTR(value, 0644,
		gpio_value_show, gpio_value_store);

static irqreturn_t gpio_sysfs_irq(int irq, void *priv)
{
	struct kernfs_node	*value_sd = priv;

	sysfs_notify_dirent(value_sd);
	return IRQ_HANDLED;
}

static int gpio_setup_irq(struct gpio_desc *desc, struct device *dev,
		unsigned long gpio_flags)
{
	struct kernfs_node	*value_sd;
	unsigned long		irq_flags;
	int			ret, irq, id;

	if ((desc->flags & GPIO_TRIGGER_MASK) == gpio_flags)
		return 0;

	irq = gpiod_to_irq(desc);
	if (irq < 0)
		return -EIO;

	id = desc->flags >> ID_SHIFT;
	value_sd = idr_find(&dirent_idr, id);
	if (value_sd)
		free_irq(irq, value_sd);

	desc->flags &= ~GPIO_TRIGGER_MASK;

	if (!gpio_flags) {
		gpiochip_unlock_as_irq(desc->chip, gpio_chip_hwgpio(desc));
		ret = 0;
		goto free_id;
	}

	irq_flags = IRQF_SHARED;
	if (test_bit(FLAG_TRIG_FALL, &gpio_flags))
		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
			IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
	if (test_bit(FLAG_TRIG_RISE, &gpio_flags))
		irq_flags |= test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
			IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;

	if (!value_sd) {
		value_sd = sysfs_get_dirent(dev->kobj.sd, "value");
		if (!value_sd) {
			ret = -ENODEV;
			goto err_out;
		}

		ret = idr_alloc(&dirent_idr, value_sd, 1, 0, GFP_KERNEL);
		if (ret < 0)
			goto free_sd;
		id = ret;

		desc->flags &= GPIO_FLAGS_MASK;
		desc->flags |= (unsigned long)id << ID_SHIFT;

		if (desc->flags >> ID_SHIFT != id) {
			ret = -ERANGE;
			goto free_id;
		}
	}

	ret = request_any_context_irq(irq, gpio_sysfs_irq, irq_flags,
				"gpiolib", value_sd);
	if (ret < 0)
		goto free_id;

	ret = gpiochip_lock_as_irq(desc->chip, gpio_chip_hwgpio(desc));
	if (ret < 0) {
		gpiod_warn(desc, "failed to flag the GPIO for IRQ\n");
		goto free_id;
	}

	desc->flags |= gpio_flags;
	return 0;

free_id:
	idr_remove(&dirent_idr, id);
	desc->flags &= GPIO_FLAGS_MASK;
free_sd:
	if (value_sd)
		sysfs_put(value_sd);
err_out:
	return ret;
}

static const struct {
	const char *name;
	unsigned long flags;
} trigger_types[] = {
	{ "none",    0 },
	{ "falling", BIT(FLAG_TRIG_FALL) },
	{ "rising",  BIT(FLAG_TRIG_RISE) },
	{ "both",    BIT(FLAG_TRIG_FALL) | BIT(FLAG_TRIG_RISE) },
};

static ssize_t gpio_edge_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	const struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else {
		int i;

		status = 0;
		for (i = 0; i < ARRAY_SIZE(trigger_types); i++)
			if ((desc->flags & GPIO_TRIGGER_MASK)
					== trigger_types[i].flags) {
				status = sprintf(buf, "%s\n",
						 trigger_types[i].name);
				break;
			}
	}

	mutex_unlock(&sysfs_lock);
	return status;
}

static ssize_t gpio_edge_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;
	int			i;

	for (i = 0; i < ARRAY_SIZE(trigger_types); i++)
		if (sysfs_streq(trigger_types[i].name, buf))
			goto found;
	return -EINVAL;

found:
	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else {
		status = gpio_setup_irq(desc, dev, trigger_types[i].flags);
		if (!status)
			status = size;
	}

	mutex_unlock(&sysfs_lock);

	return status;
}

static DEVICE_ATTR(edge, 0644, gpio_edge_show, gpio_edge_store);

static int sysfs_set_active_low(struct gpio_desc *desc, struct device *dev,
				int value)
{
	int			status = 0;

	if (!!test_bit(FLAG_ACTIVE_LOW, &desc->flags) == !!value)
		return 0;

	if (value)
		set_bit(FLAG_ACTIVE_LOW, &desc->flags);
	else
		clear_bit(FLAG_ACTIVE_LOW, &desc->flags);

	/* reconfigure poll(2) support if enabled on one edge only */
	if (dev != NULL && (!!test_bit(FLAG_TRIG_RISE, &desc->flags) ^
				!!test_bit(FLAG_TRIG_FALL, &desc->flags))) {
		unsigned long trigger_flags = desc->flags & GPIO_TRIGGER_MASK;

		gpio_setup_irq(desc, dev, 0);
		status = gpio_setup_irq(desc, dev, trigger_flags);
	}

	return status;
}

static ssize_t gpio_active_low_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	const struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags))
		status = -EIO;
	else
		status = sprintf(buf, "%d\n",
				!!test_bit(FLAG_ACTIVE_LOW, &desc->flags));

	mutex_unlock(&sysfs_lock);

	return status;
}

static ssize_t gpio_active_low_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t size)
{
	struct gpio_desc	*desc = dev_get_drvdata(dev);
	ssize_t			status;

	mutex_lock(&sysfs_lock);

	if (!test_bit(FLAG_EXPORT, &desc->flags)) {
		status = -EIO;
	} else {
		long		value;

		status = kstrtol(buf, 0, &value);
		if (status == 0)
			status = sysfs_set_active_low(desc, dev, value != 0);
	}

	mutex_unlock(&sysfs_lock);

	return status ? : size;
}

static DEVICE_ATTR(active_low, 0644,
		gpio_active_low_show, gpio_active_low_store);

static umode_t gpio_is_visible(struct kobject *kobj, struct attribute *attr,
			       int n)
{
	struct device *dev = container_of(kobj, struct device, kobj);
	struct gpio_desc *desc = dev_get_drvdata(dev);
	umode_t mode = attr->mode;
	bool show_direction = test_bit(FLAG_SYSFS_DIR, &desc->flags);

	if (attr == &dev_attr_direction.attr) {
		if (!show_direction)
			mode = 0;
	} else if (attr == &dev_attr_edge.attr) {
		if (gpiod_to_irq(desc) < 0)
			mode = 0;
		if (!show_direction && test_bit(FLAG_IS_OUT, &desc->flags))
			mode = 0;
	}

	return mode;
}

static struct attribute *gpio_attrs[] = {
	&dev_attr_direction.attr,
	&dev_attr_edge.attr,
	&dev_attr_value.attr,
	&dev_attr_active_low.attr,
	NULL,
};

static const struct attribute_group gpio_group = {
	.attrs = gpio_attrs,
	.is_visible = gpio_is_visible,
};

static const struct attribute_group *gpio_groups[] = {
	&gpio_group,
	NULL
};

/*
 * /sys/class/gpio/gpiochipN/
 *   /base ... matching gpio_chip.base (N)
 *   /label ... matching gpio_chip.label
 *   /ngpio ... matching gpio_chip.ngpio
 */

static ssize_t chip_base_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", chip->base);
}
static DEVICE_ATTR(base, 0444, chip_base_show, NULL);

static ssize_t chip_label_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%s\n", chip->label ? : "");
}
static DEVICE_ATTR(label, 0444, chip_label_show, NULL);

static ssize_t chip_ngpio_show(struct device *dev,
			       struct device_attribute *attr, char *buf)
{
	const struct gpio_chip	*chip = dev_get_drvdata(dev);

	return sprintf(buf, "%u\n", chip->ngpio);
}
static DEVICE_ATTR(ngpio, 0444, chip_ngpio_show, NULL);

static struct attribute *gpiochip_attrs[] = {
	&dev_attr_base.attr,
	&dev_attr_label.attr,
	&dev_attr_ngpio.attr,
	NULL,
};
ATTRIBUTE_GROUPS(gpiochip);

/*
 * /sys/class/gpio/export ... write-only
 *	integer N ... number of GPIO to export (full access)
 * /sys/class/gpio/unexport ... write-only
 *	integer N ... number of GPIO to unexport
 */
static ssize_t export_store(struct class *class,
				struct class_attribute *attr,
				const char *buf, size_t len)
{
	long			gpio;
	struct gpio_desc	*desc;
	int			status;

	status = kstrtol(buf, 0, &gpio);
	if (status < 0)
		goto done;

	desc = gpio_to_desc(gpio);
	/* reject invalid GPIOs */
	if (!desc) {
		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
		return -EINVAL;
	}

	/* No extra locking here; FLAG_SYSFS just signifies that the
	 * request and export were done by on behalf of userspace, so
	 * they may be undone on its behalf too.
	 */

	status = gpiod_request(desc, "sysfs");
	if (status < 0) {
		if (status == -EPROBE_DEFER)
			status = -ENODEV;
		goto done;
	}
	status = gpiod_export(desc, true);
	if (status < 0)
		gpiod_free(desc);
	else
		set_bit(FLAG_SYSFS, &desc->flags);

done:
	if (status)
		pr_debug("%s: status %d\n", __func__, status);
	return status ? : len;
}

static ssize_t unexport_store(struct class *class,
				struct class_attribute *attr,
				const char *buf, size_t len)
{
	long			gpio;
	struct gpio_desc	*desc;
	int			status;

	status = kstrtol(buf, 0, &gpio);
	if (status < 0)
		goto done;

	desc = gpio_to_desc(gpio);
	/* reject bogus commands (gpio_unexport ignores them) */
	if (!desc) {
		pr_warn("%s: invalid GPIO %ld\n", __func__, gpio);
		return -EINVAL;
	}

	status = -EINVAL;

	/* No extra locking here; FLAG_SYSFS just signifies that the
	 * request and export were done by on behalf of userspace, so
	 * they may be undone on its behalf too.
	 */
	if (test_and_clear_bit(FLAG_SYSFS, &desc->flags)) {
		status = 0;
		gpiod_free(desc);
	}
done:
	if (status)
		pr_debug("%s: status %d\n", __func__, status);
	return status ? : len;
}

static struct class_attribute gpio_class_attrs[] = {
	__ATTR(export, 0200, NULL, export_store),
	__ATTR(unexport, 0200, NULL, unexport_store),
	__ATTR_NULL,
};

static struct class gpio_class = {
	.name =		"gpio",
	.owner =	THIS_MODULE,

	.class_attrs =	gpio_class_attrs,
};


/**
 * gpiod_export - export a GPIO through sysfs
 * @gpio: gpio to make available, already requested
 * @direction_may_change: true if userspace may change gpio direction
 * Context: arch_initcall or later
 *
 * When drivers want to make a GPIO accessible to userspace after they
 * have requested it -- perhaps while debugging, or as part of their
 * public interface -- they may use this routine.  If the GPIO can
 * change direction (some can't) and the caller allows it, userspace
 * will see "direction" sysfs attribute which may be used to change
 * the gpio's direction.  A "value" attribute will always be provided.
 *
 * Returns zero on success, else an error.
 */
int gpiod_export(struct gpio_desc *desc, bool direction_may_change)
{
	struct gpio_chip	*chip;
	unsigned long		flags;
	int			status;
	const char		*ioname = NULL;
	struct device		*dev;
	int			offset;

	/* can't export until sysfs is available ... */
	if (!gpio_class.p) {
		pr_debug("%s: called too early!\n", __func__);
		return -ENOENT;
	}

	if (!desc) {
		pr_debug("%s: invalid gpio descriptor\n", __func__);
		return -EINVAL;
	}

	chip = desc->chip;

	mutex_lock(&sysfs_lock);

	/* check if chip is being removed */
	if (!chip || !chip->exported) {
		status = -ENODEV;
		goto fail_unlock;
	}

	spin_lock_irqsave(&gpio_lock, flags);
	if (!test_bit(FLAG_REQUESTED, &desc->flags) ||
	     test_bit(FLAG_EXPORT, &desc->flags)) {
		spin_unlock_irqrestore(&gpio_lock, flags);
		gpiod_dbg(desc, "%s: unavailable (requested=%d, exported=%d)\n",
				__func__,
				test_bit(FLAG_REQUESTED, &desc->flags),
				test_bit(FLAG_EXPORT, &desc->flags));
		status = -EPERM;
		goto fail_unlock;
	}

	if (desc->chip->direction_input && desc->chip->direction_output &&
			direction_may_change) {
		set_bit(FLAG_SYSFS_DIR, &desc->flags);
	}

	spin_unlock_irqrestore(&gpio_lock, flags);

	offset = gpio_chip_hwgpio(desc);
	if (desc->chip->names && desc->chip->names[offset])
		ioname = desc->chip->names[offset];

	dev = device_create_with_groups(&gpio_class, desc->chip->dev,
					MKDEV(0, 0), desc, gpio_groups,
					ioname ? ioname : "gpio%u",
					desc_to_gpio(desc));
	if (IS_ERR(dev)) {
		status = PTR_ERR(dev);
		goto fail_unlock;
	}

	set_bit(FLAG_EXPORT, &desc->flags);
	mutex_unlock(&sysfs_lock);
	return 0;

fail_unlock:
	mutex_unlock(&sysfs_lock);
	gpiod_dbg(desc, "%s: status %d\n", __func__, status);
	return status;
}
EXPORT_SYMBOL_GPL(gpiod_export);

static int match_export(struct device *dev, const void *data)
{
	return dev_get_drvdata(dev) == data;
}

/**
 * gpiod_export_link - create a sysfs link to an exported GPIO node
 * @dev: device under which to create symlink
 * @name: name of the symlink
 * @gpio: gpio to create symlink to, already exported
 *
 * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
 * node. Caller is responsible for unlinking.
 *
 * Returns zero on success, else an error.
 */
int gpiod_export_link(struct device *dev, const char *name,
		      struct gpio_desc *desc)
{
	int			status = -EINVAL;

	if (!desc) {
		pr_warn("%s: invalid GPIO\n", __func__);
		return -EINVAL;
	}

	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {
		struct device *tdev;

		tdev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (tdev != NULL) {
			status = sysfs_create_link(&dev->kobj, &tdev->kobj,
						name);
			put_device(tdev);
		} else {
			status = -ENODEV;
		}
	}

	mutex_unlock(&sysfs_lock);

	if (status)
		gpiod_dbg(desc, "%s: status %d\n", __func__, status);

	return status;
}
EXPORT_SYMBOL_GPL(gpiod_export_link);

/**
 * gpiod_sysfs_set_active_low - set the polarity of gpio sysfs value
 * @gpio: gpio to change
 * @value: non-zero to use active low, i.e. inverted values
 *
 * Set the polarity of /sys/class/gpio/gpioN/value sysfs attribute.
 * The GPIO does not have to be exported yet.  If poll(2) support has
 * been enabled for either rising or falling edge, it will be
 * reconfigured to follow the new polarity.
 *
 * Returns zero on success, else an error.
 */
int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
{
	struct device		*dev = NULL;
	int			status = -EINVAL;

	if (!desc) {
		pr_warn("%s: invalid GPIO\n", __func__);
		return -EINVAL;
	}

	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {
		dev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (dev == NULL) {
			status = -ENODEV;
			goto unlock;
		}
	}

	status = sysfs_set_active_low(desc, dev, value);
	put_device(dev);
unlock:
	mutex_unlock(&sysfs_lock);

	if (status)
		gpiod_dbg(desc, "%s: status %d\n", __func__, status);

	return status;
}
EXPORT_SYMBOL_GPL(gpiod_sysfs_set_active_low);

/**
 * gpiod_unexport - reverse effect of gpio_export()
 * @gpio: gpio to make unavailable
 *
 * This is implicit on gpio_free().
 */
void gpiod_unexport(struct gpio_desc *desc)
{
	int			status = 0;
	struct device		*dev = NULL;

	if (!desc) {
		pr_warn("%s: invalid GPIO\n", __func__);
		return;
	}

	mutex_lock(&sysfs_lock);

	if (test_bit(FLAG_EXPORT, &desc->flags)) {

		dev = class_find_device(&gpio_class, NULL, desc, match_export);
		if (dev) {
			gpio_setup_irq(desc, dev, 0);
			clear_bit(FLAG_SYSFS_DIR, &desc->flags);
			clear_bit(FLAG_EXPORT, &desc->flags);
		} else
			status = -ENODEV;
	}

	mutex_unlock(&sysfs_lock);

	if (dev) {
		device_unregister(dev);
		put_device(dev);
	}

	if (status)
		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
}
EXPORT_SYMBOL_GPL(gpiod_unexport);

int gpiochip_export(struct gpio_chip *chip)
{
	int		status;
	struct device	*dev;

	/* Many systems register gpio chips for SOC support very early,
	 * before driver model support is available.  In those cases we
	 * export this later, in gpiolib_sysfs_init() ... here we just
	 * verify that _some_ field of gpio_class got initialized.
	 */
	if (!gpio_class.p)
		return 0;

	/* use chip->base for the ID; it's already known to be unique */
	mutex_lock(&sysfs_lock);
	dev = device_create_with_groups(&gpio_class, chip->dev, MKDEV(0, 0),
					chip, gpiochip_groups,
					"gpiochip%d", chip->base);
	if (IS_ERR(dev))
		status = PTR_ERR(dev);
	else
		status = 0;
	chip->exported = (status == 0);
	mutex_unlock(&sysfs_lock);

	if (status)
		chip_dbg(chip, "%s: status %d\n", __func__, status);

	return status;
}

void gpiochip_unexport(struct gpio_chip *chip)
{
	int			status;
	struct device		*dev;
	struct gpio_desc *desc;
	unsigned int i;

	mutex_lock(&sysfs_lock);
	dev = class_find_device(&gpio_class, NULL, chip, match_export);
	if (dev) {
		put_device(dev);
		device_unregister(dev);
		/* prevent further gpiod exports */
		chip->exported = false;
		status = 0;
	} else
		status = -ENODEV;
	mutex_unlock(&sysfs_lock);

	if (status)
		chip_dbg(chip, "%s: status %d\n", __func__, status);

	/* unregister gpiod class devices owned by sysfs */
	for (i = 0; i < chip->ngpio; i++) {
		desc = &chip->desc[i];
		if (test_and_clear_bit(FLAG_SYSFS, &desc->flags))
			gpiod_free(desc);
	}
}

static int __init gpiolib_sysfs_init(void)
{
	int		status;
	unsigned long	flags;
	struct gpio_chip *chip;

	status = class_register(&gpio_class);
	if (status < 0)
		return status;

	/* Scan and register the gpio_chips which registered very
	 * early (e.g. before the class_register above was called).
	 *
	 * We run before arch_initcall() so chip->dev nodes can have
	 * registered, and so arch_initcall() can always gpio_export().
	 */
	spin_lock_irqsave(&gpio_lock, flags);
	list_for_each_entry(chip, &gpio_chips, list) {
		if (chip->exported)
			continue;

		/*
		 * TODO we yield gpio_lock here because gpiochip_export()
		 * acquires a mutex. This is unsafe and needs to be fixed.
		 *
		 * Also it would be nice to use gpiochip_find() here so we
		 * can keep gpio_chips local to gpiolib.c, but the yield of
		 * gpio_lock prevents us from doing this.
		 */
		spin_unlock_irqrestore(&gpio_lock, flags);
		status = gpiochip_export(chip);
		spin_lock_irqsave(&gpio_lock, flags);
	}
	spin_unlock_irqrestore(&gpio_lock, flags);


	return status;
}
postcore_initcall(gpiolib_sysfs_init);