1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Backlight Lowlevel Control Abstraction
4 *
5 * Copyright (C) 2003,2004 Hewlett-Packard Company
6 *
7 */
8
9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11#include <linux/module.h>
12#include <linux/init.h>
13#include <linux/device.h>
14#include <linux/backlight.h>
15#include <linux/notifier.h>
16#include <linux/ctype.h>
17#include <linux/err.h>
18#include <linux/fb.h>
19#include <linux/slab.h>
20
21#ifdef CONFIG_PMAC_BACKLIGHT
22#include <asm/backlight.h>
23#endif
24
25/**
26 * DOC: overview
27 *
28 * The backlight core supports implementing backlight drivers.
29 *
30 * A backlight driver registers a driver using
31 * devm_backlight_device_register(). The properties of the backlight
32 * driver such as type and max_brightness must be specified.
33 * When the core detect changes in for example brightness or power state
34 * the update_status() operation is called. The backlight driver shall
35 * implement this operation and use it to adjust backlight.
36 *
37 * Several sysfs attributes are provided by the backlight core::
38 *
39 * - brightness R/W, set the requested brightness level
40 * - actual_brightness RO, the brightness level used by the HW
41 * - max_brightness RO, the maximum brightness level supported
42 *
43 * See Documentation/ABI/stable/sysfs-class-backlight for the full list.
44 *
45 * The backlight can be adjusted using the sysfs interface, and
46 * the backlight driver may also support adjusting backlight using
47 * a hot-key or some other platform or firmware specific way.
48 *
49 * The driver must implement the get_brightness() operation if
50 * the HW do not support all the levels that can be specified in
51 * brightness, thus providing user-space access to the actual level
52 * via the actual_brightness attribute.
53 *
54 * When the backlight changes this is reported to user-space using
55 * an uevent connected to the actual_brightness attribute.
56 * When brightness is set by platform specific means, for example
57 * a hot-key to adjust backlight, the driver must notify the backlight
58 * core that brightness has changed using backlight_force_update().
59 *
60 * The backlight driver core receives notifications from fbdev and
61 * if the event is FB_EVENT_BLANK and if the value of blank, from the
62 * FBIOBLANK ioctrl, results in a change in the backlight state the
63 * update_status() operation is called.
64 */
65
66static struct list_head backlight_dev_list;
67static struct mutex backlight_dev_list_mutex;
68static struct blocking_notifier_head backlight_notifier;
69
70static const char *const backlight_types[] = {
71 [BACKLIGHT_RAW] = "raw",
72 [BACKLIGHT_PLATFORM] = "platform",
73 [BACKLIGHT_FIRMWARE] = "firmware",
74};
75
76static const char *const backlight_scale_types[] = {
77 [BACKLIGHT_SCALE_UNKNOWN] = "unknown",
78 [BACKLIGHT_SCALE_LINEAR] = "linear",
79 [BACKLIGHT_SCALE_NON_LINEAR] = "non-linear",
80};
81
82#if defined(CONFIG_FB_CORE) || (defined(CONFIG_FB_CORE_MODULE) && \
83 defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
84/*
85 * fb_notifier_callback
86 *
87 * This callback gets called when something important happens inside a
88 * framebuffer driver. The backlight core only cares about FB_BLANK_UNBLANK
89 * which is reported to the driver using backlight_update_status()
90 * as a state change.
91 *
92 * There may be several fbdev's connected to the backlight device,
93 * in which case they are kept track of. A state change is only reported
94 * if there is a change in backlight for the specified fbdev.
95 */
96static int fb_notifier_callback(struct notifier_block *self,
97 unsigned long event, void *data)
98{
99 struct backlight_device *bd;
100 struct fb_event *evdata = data;
101 int node = evdata->info->node;
102 int fb_blank = 0;
103
104 /* If we aren't interested in this event, skip it immediately ... */
105 if (event != FB_EVENT_BLANK)
106 return 0;
107
108 bd = container_of(self, struct backlight_device, fb_notif);
109 mutex_lock(&bd->ops_lock);
110
111 if (!bd->ops)
112 goto out;
113 if (bd->ops->check_fb && !bd->ops->check_fb(bd, evdata->info))
114 goto out;
115
116 fb_blank = *(int *)evdata->data;
117 if (fb_blank == FB_BLANK_UNBLANK && !bd->fb_bl_on[node]) {
118 bd->fb_bl_on[node] = true;
119 if (!bd->use_count++) {
120 bd->props.state &= ~BL_CORE_FBBLANK;
121 bd->props.fb_blank = FB_BLANK_UNBLANK;
122 backlight_update_status(bd);
123 }
124 } else if (fb_blank != FB_BLANK_UNBLANK && bd->fb_bl_on[node]) {
125 bd->fb_bl_on[node] = false;
126 if (!(--bd->use_count)) {
127 bd->props.state |= BL_CORE_FBBLANK;
128 bd->props.fb_blank = fb_blank;
129 backlight_update_status(bd);
130 }
131 }
132out:
133 mutex_unlock(lock: &bd->ops_lock);
134 return 0;
135}
136
137static int backlight_register_fb(struct backlight_device *bd)
138{
139 memset(&bd->fb_notif, 0, sizeof(bd->fb_notif));
140 bd->fb_notif.notifier_call = fb_notifier_callback;
141
142 return fb_register_client(nb: &bd->fb_notif);
143}
144
145static void backlight_unregister_fb(struct backlight_device *bd)
146{
147 fb_unregister_client(nb: &bd->fb_notif);
148}
149#else
150static inline int backlight_register_fb(struct backlight_device *bd)
151{
152 return 0;
153}
154
155static inline void backlight_unregister_fb(struct backlight_device *bd)
156{
157}
158#endif /* CONFIG_FB_CORE */
159
160static void backlight_generate_event(struct backlight_device *bd,
161 enum backlight_update_reason reason)
162{
163 char *envp[2];
164
165 switch (reason) {
166 case BACKLIGHT_UPDATE_SYSFS:
167 envp[0] = "SOURCE=sysfs";
168 break;
169 case BACKLIGHT_UPDATE_HOTKEY:
170 envp[0] = "SOURCE=hotkey";
171 break;
172 default:
173 envp[0] = "SOURCE=unknown";
174 break;
175 }
176 envp[1] = NULL;
177 kobject_uevent_env(kobj: &bd->dev.kobj, action: KOBJ_CHANGE, envp);
178 sysfs_notify(kobj: &bd->dev.kobj, NULL, attr: "actual_brightness");
179}
180
181static ssize_t bl_power_show(struct device *dev, struct device_attribute *attr,
182 char *buf)
183{
184 struct backlight_device *bd = to_backlight_device(dev);
185
186 return sprintf(buf, fmt: "%d\n", bd->props.power);
187}
188
189static ssize_t bl_power_store(struct device *dev, struct device_attribute *attr,
190 const char *buf, size_t count)
191{
192 int rc;
193 struct backlight_device *bd = to_backlight_device(dev);
194 unsigned long power, old_power;
195
196 rc = kstrtoul(s: buf, base: 0, res: &power);
197 if (rc)
198 return rc;
199
200 rc = -ENXIO;
201 mutex_lock(&bd->ops_lock);
202 if (bd->ops) {
203 pr_debug("set power to %lu\n", power);
204 if (bd->props.power != power) {
205 old_power = bd->props.power;
206 bd->props.power = power;
207 rc = backlight_update_status(bd);
208 if (rc)
209 bd->props.power = old_power;
210 else
211 rc = count;
212 } else {
213 rc = count;
214 }
215 }
216 mutex_unlock(lock: &bd->ops_lock);
217
218 return rc;
219}
220static DEVICE_ATTR_RW(bl_power);
221
222static ssize_t brightness_show(struct device *dev,
223 struct device_attribute *attr, char *buf)
224{
225 struct backlight_device *bd = to_backlight_device(dev);
226
227 return sprintf(buf, fmt: "%d\n", bd->props.brightness);
228}
229
230int backlight_device_set_brightness(struct backlight_device *bd,
231 unsigned long brightness)
232{
233 int rc = -ENXIO;
234
235 mutex_lock(&bd->ops_lock);
236 if (bd->ops) {
237 if (brightness > bd->props.max_brightness)
238 rc = -EINVAL;
239 else {
240 pr_debug("set brightness to %lu\n", brightness);
241 bd->props.brightness = brightness;
242 rc = backlight_update_status(bd);
243 }
244 }
245 mutex_unlock(lock: &bd->ops_lock);
246
247 backlight_generate_event(bd, reason: BACKLIGHT_UPDATE_SYSFS);
248
249 return rc;
250}
251EXPORT_SYMBOL(backlight_device_set_brightness);
252
253static ssize_t brightness_store(struct device *dev,
254 struct device_attribute *attr, const char *buf, size_t count)
255{
256 int rc;
257 struct backlight_device *bd = to_backlight_device(dev);
258 unsigned long brightness;
259
260 rc = kstrtoul(s: buf, base: 0, res: &brightness);
261 if (rc)
262 return rc;
263
264 rc = backlight_device_set_brightness(bd, brightness);
265
266 return rc ? rc : count;
267}
268static DEVICE_ATTR_RW(brightness);
269
270static ssize_t type_show(struct device *dev, struct device_attribute *attr,
271 char *buf)
272{
273 struct backlight_device *bd = to_backlight_device(dev);
274
275 return sprintf(buf, fmt: "%s\n", backlight_types[bd->props.type]);
276}
277static DEVICE_ATTR_RO(type);
278
279static ssize_t max_brightness_show(struct device *dev,
280 struct device_attribute *attr, char *buf)
281{
282 struct backlight_device *bd = to_backlight_device(dev);
283
284 return sprintf(buf, fmt: "%d\n", bd->props.max_brightness);
285}
286static DEVICE_ATTR_RO(max_brightness);
287
288static ssize_t actual_brightness_show(struct device *dev,
289 struct device_attribute *attr, char *buf)
290{
291 int rc = -ENXIO;
292 struct backlight_device *bd = to_backlight_device(dev);
293
294 mutex_lock(&bd->ops_lock);
295 if (bd->ops && bd->ops->get_brightness) {
296 rc = bd->ops->get_brightness(bd);
297 if (rc >= 0)
298 rc = sprintf(buf, fmt: "%d\n", rc);
299 } else {
300 rc = sprintf(buf, fmt: "%d\n", bd->props.brightness);
301 }
302 mutex_unlock(lock: &bd->ops_lock);
303
304 return rc;
305}
306static DEVICE_ATTR_RO(actual_brightness);
307
308static ssize_t scale_show(struct device *dev,
309 struct device_attribute *attr, char *buf)
310{
311 struct backlight_device *bd = to_backlight_device(dev);
312
313 if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR))
314 return sprintf(buf, fmt: "unknown\n");
315
316 return sprintf(buf, fmt: "%s\n", backlight_scale_types[bd->props.scale]);
317}
318static DEVICE_ATTR_RO(scale);
319
320static struct class *backlight_class;
321
322#ifdef CONFIG_PM_SLEEP
323static int backlight_suspend(struct device *dev)
324{
325 struct backlight_device *bd = to_backlight_device(dev);
326
327 mutex_lock(&bd->ops_lock);
328 if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
329 bd->props.state |= BL_CORE_SUSPENDED;
330 backlight_update_status(bd);
331 }
332 mutex_unlock(lock: &bd->ops_lock);
333
334 return 0;
335}
336
337static int backlight_resume(struct device *dev)
338{
339 struct backlight_device *bd = to_backlight_device(dev);
340
341 mutex_lock(&bd->ops_lock);
342 if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
343 bd->props.state &= ~BL_CORE_SUSPENDED;
344 backlight_update_status(bd);
345 }
346 mutex_unlock(lock: &bd->ops_lock);
347
348 return 0;
349}
350#endif
351
352static SIMPLE_DEV_PM_OPS(backlight_class_dev_pm_ops, backlight_suspend,
353 backlight_resume);
354
355static void bl_device_release(struct device *dev)
356{
357 struct backlight_device *bd = to_backlight_device(dev);
358 kfree(objp: bd);
359}
360
361static struct attribute *bl_device_attrs[] = {
362 &dev_attr_bl_power.attr,
363 &dev_attr_brightness.attr,
364 &dev_attr_actual_brightness.attr,
365 &dev_attr_max_brightness.attr,
366 &dev_attr_scale.attr,
367 &dev_attr_type.attr,
368 NULL,
369};
370ATTRIBUTE_GROUPS(bl_device);
371
372/**
373 * backlight_force_update - tell the backlight subsystem that hardware state
374 * has changed
375 * @bd: the backlight device to update
376 * @reason: reason for update
377 *
378 * Updates the internal state of the backlight in response to a hardware event,
379 * and generates an uevent to notify userspace. A backlight driver shall call
380 * backlight_force_update() when the backlight is changed using, for example,
381 * a hot-key. The updated brightness is read using get_brightness() and the
382 * brightness value is reported using an uevent.
383 */
384void backlight_force_update(struct backlight_device *bd,
385 enum backlight_update_reason reason)
386{
387 int brightness;
388
389 mutex_lock(&bd->ops_lock);
390 if (bd->ops && bd->ops->get_brightness) {
391 brightness = bd->ops->get_brightness(bd);
392 if (brightness >= 0)
393 bd->props.brightness = brightness;
394 else
395 dev_err(&bd->dev,
396 "Could not update brightness from device: %pe\n",
397 ERR_PTR(brightness));
398 }
399 mutex_unlock(lock: &bd->ops_lock);
400 backlight_generate_event(bd, reason);
401}
402EXPORT_SYMBOL(backlight_force_update);
403
404/* deprecated - use devm_backlight_device_register() */
405struct backlight_device *backlight_device_register(const char *name,
406 struct device *parent, void *devdata, const struct backlight_ops *ops,
407 const struct backlight_properties *props)
408{
409 struct backlight_device *new_bd;
410 int rc;
411
412 pr_debug("backlight_device_register: name=%s\n", name);
413
414 new_bd = kzalloc(size: sizeof(struct backlight_device), GFP_KERNEL);
415 if (!new_bd)
416 return ERR_PTR(error: -ENOMEM);
417
418 mutex_init(&new_bd->update_lock);
419 mutex_init(&new_bd->ops_lock);
420
421 new_bd->dev.class = backlight_class;
422 new_bd->dev.parent = parent;
423 new_bd->dev.release = bl_device_release;
424 dev_set_name(dev: &new_bd->dev, name: "%s", name);
425 dev_set_drvdata(dev: &new_bd->dev, data: devdata);
426
427 /* Set default properties */
428 if (props) {
429 memcpy(&new_bd->props, props,
430 sizeof(struct backlight_properties));
431 if (props->type <= 0 || props->type >= BACKLIGHT_TYPE_MAX) {
432 WARN(1, "%s: invalid backlight type", name);
433 new_bd->props.type = BACKLIGHT_RAW;
434 }
435 } else {
436 new_bd->props.type = BACKLIGHT_RAW;
437 }
438
439 rc = device_register(dev: &new_bd->dev);
440 if (rc) {
441 put_device(dev: &new_bd->dev);
442 return ERR_PTR(error: rc);
443 }
444
445 rc = backlight_register_fb(bd: new_bd);
446 if (rc) {
447 device_unregister(dev: &new_bd->dev);
448 return ERR_PTR(error: rc);
449 }
450
451 new_bd->ops = ops;
452
453#ifdef CONFIG_PMAC_BACKLIGHT
454 mutex_lock(&pmac_backlight_mutex);
455 if (!pmac_backlight)
456 pmac_backlight = new_bd;
457 mutex_unlock(&pmac_backlight_mutex);
458#endif
459
460 mutex_lock(&backlight_dev_list_mutex);
461 list_add(new: &new_bd->entry, head: &backlight_dev_list);
462 mutex_unlock(lock: &backlight_dev_list_mutex);
463
464 blocking_notifier_call_chain(nh: &backlight_notifier,
465 val: BACKLIGHT_REGISTERED, v: new_bd);
466
467 return new_bd;
468}
469EXPORT_SYMBOL(backlight_device_register);
470
471/** backlight_device_get_by_type - find first backlight device of a type
472 * @type: the type of backlight device
473 *
474 * Look up the first backlight device of the specified type
475 *
476 * RETURNS:
477 *
478 * Pointer to backlight device if any was found. Otherwise NULL.
479 */
480struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
481{
482 bool found = false;
483 struct backlight_device *bd;
484
485 mutex_lock(&backlight_dev_list_mutex);
486 list_for_each_entry(bd, &backlight_dev_list, entry) {
487 if (bd->props.type == type) {
488 found = true;
489 break;
490 }
491 }
492 mutex_unlock(lock: &backlight_dev_list_mutex);
493
494 return found ? bd : NULL;
495}
496EXPORT_SYMBOL(backlight_device_get_by_type);
497
498/**
499 * backlight_device_get_by_name - Get backlight device by name
500 * @name: Device name
501 *
502 * This function looks up a backlight device by its name. It obtains a reference
503 * on the backlight device and it is the caller's responsibility to drop the
504 * reference by calling put_device().
505 *
506 * Returns:
507 * A pointer to the backlight device if found, otherwise NULL.
508 */
509struct backlight_device *backlight_device_get_by_name(const char *name)
510{
511 struct device *dev;
512
513 dev = class_find_device_by_name(class: backlight_class, name);
514
515 return dev ? to_backlight_device(dev) : NULL;
516}
517EXPORT_SYMBOL(backlight_device_get_by_name);
518
519/* deprecated - use devm_backlight_device_unregister() */
520void backlight_device_unregister(struct backlight_device *bd)
521{
522 if (!bd)
523 return;
524
525 mutex_lock(&backlight_dev_list_mutex);
526 list_del(entry: &bd->entry);
527 mutex_unlock(lock: &backlight_dev_list_mutex);
528
529#ifdef CONFIG_PMAC_BACKLIGHT
530 mutex_lock(&pmac_backlight_mutex);
531 if (pmac_backlight == bd)
532 pmac_backlight = NULL;
533 mutex_unlock(&pmac_backlight_mutex);
534#endif
535
536 blocking_notifier_call_chain(nh: &backlight_notifier,
537 val: BACKLIGHT_UNREGISTERED, v: bd);
538
539 mutex_lock(&bd->ops_lock);
540 bd->ops = NULL;
541 mutex_unlock(lock: &bd->ops_lock);
542
543 backlight_unregister_fb(bd);
544 device_unregister(dev: &bd->dev);
545}
546EXPORT_SYMBOL(backlight_device_unregister);
547
548static void devm_backlight_device_release(struct device *dev, void *res)
549{
550 struct backlight_device *backlight = *(struct backlight_device **)res;
551
552 backlight_device_unregister(backlight);
553}
554
555static int devm_backlight_device_match(struct device *dev, void *res,
556 void *data)
557{
558 struct backlight_device **r = res;
559
560 return *r == data;
561}
562
563/**
564 * backlight_register_notifier - get notified of backlight (un)registration
565 * @nb: notifier block with the notifier to call on backlight (un)registration
566 *
567 * Register a notifier to get notified when backlight devices get registered
568 * or unregistered.
569 *
570 * RETURNS:
571 *
572 * 0 on success, otherwise a negative error code
573 */
574int backlight_register_notifier(struct notifier_block *nb)
575{
576 return blocking_notifier_chain_register(nh: &backlight_notifier, nb);
577}
578EXPORT_SYMBOL(backlight_register_notifier);
579
580/**
581 * backlight_unregister_notifier - unregister a backlight notifier
582 * @nb: notifier block to unregister
583 *
584 * Register a notifier to get notified when backlight devices get registered
585 * or unregistered.
586 *
587 * RETURNS:
588 *
589 * 0 on success, otherwise a negative error code
590 */
591int backlight_unregister_notifier(struct notifier_block *nb)
592{
593 return blocking_notifier_chain_unregister(nh: &backlight_notifier, nb);
594}
595EXPORT_SYMBOL(backlight_unregister_notifier);
596
597/**
598 * devm_backlight_device_register - register a new backlight device
599 * @dev: the device to register
600 * @name: the name of the device
601 * @parent: a pointer to the parent device (often the same as @dev)
602 * @devdata: an optional pointer to be stored for private driver use
603 * @ops: the backlight operations structure
604 * @props: the backlight properties
605 *
606 * Creates and registers new backlight device. When a backlight device
607 * is registered the configuration must be specified in the @props
608 * parameter. See description of &backlight_properties.
609 *
610 * RETURNS:
611 *
612 * struct backlight on success, or an ERR_PTR on error
613 */
614struct backlight_device *devm_backlight_device_register(struct device *dev,
615 const char *name, struct device *parent, void *devdata,
616 const struct backlight_ops *ops,
617 const struct backlight_properties *props)
618{
619 struct backlight_device **ptr, *backlight;
620
621 ptr = devres_alloc(devm_backlight_device_release, sizeof(*ptr),
622 GFP_KERNEL);
623 if (!ptr)
624 return ERR_PTR(error: -ENOMEM);
625
626 backlight = backlight_device_register(name, parent, devdata, ops,
627 props);
628 if (!IS_ERR(ptr: backlight)) {
629 *ptr = backlight;
630 devres_add(dev, res: ptr);
631 } else {
632 devres_free(res: ptr);
633 }
634
635 return backlight;
636}
637EXPORT_SYMBOL(devm_backlight_device_register);
638
639/**
640 * devm_backlight_device_unregister - unregister backlight device
641 * @dev: the device to unregister
642 * @bd: the backlight device to unregister
643 *
644 * Deallocates a backlight allocated with devm_backlight_device_register().
645 * Normally this function will not need to be called and the resource management
646 * code will ensure that the resources are freed.
647 */
648void devm_backlight_device_unregister(struct device *dev,
649 struct backlight_device *bd)
650{
651 int rc;
652
653 rc = devres_release(dev, release: devm_backlight_device_release,
654 match: devm_backlight_device_match, match_data: bd);
655 WARN_ON(rc);
656}
657EXPORT_SYMBOL(devm_backlight_device_unregister);
658
659#ifdef CONFIG_OF
660static int of_parent_match(struct device *dev, const void *data)
661{
662 return dev->parent && dev->parent->of_node == data;
663}
664
665/**
666 * of_find_backlight_by_node() - find backlight device by device-tree node
667 * @node: device-tree node of the backlight device
668 *
669 * Returns a pointer to the backlight device corresponding to the given DT
670 * node or NULL if no such backlight device exists or if the device hasn't
671 * been probed yet.
672 *
673 * This function obtains a reference on the backlight device and it is the
674 * caller's responsibility to drop the reference by calling put_device() on
675 * the backlight device's .dev field.
676 */
677struct backlight_device *of_find_backlight_by_node(struct device_node *node)
678{
679 struct device *dev;
680
681 dev = class_find_device(class: backlight_class, NULL, data: node, match: of_parent_match);
682
683 return dev ? to_backlight_device(dev) : NULL;
684}
685EXPORT_SYMBOL(of_find_backlight_by_node);
686#endif
687
688static struct backlight_device *of_find_backlight(struct device *dev)
689{
690 struct backlight_device *bd = NULL;
691 struct device_node *np;
692
693 if (!dev)
694 return NULL;
695
696 if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
697 np = of_parse_phandle(np: dev->of_node, phandle_name: "backlight", index: 0);
698 if (np) {
699 bd = of_find_backlight_by_node(np);
700 of_node_put(node: np);
701 if (!bd)
702 return ERR_PTR(error: -EPROBE_DEFER);
703 }
704 }
705
706 return bd;
707}
708
709static void devm_backlight_release(void *data)
710{
711 struct backlight_device *bd = data;
712
713 put_device(dev: &bd->dev);
714}
715
716/**
717 * devm_of_find_backlight - find backlight for a device
718 * @dev: the device
719 *
720 * This function looks for a property named 'backlight' on the DT node
721 * connected to @dev and looks up the backlight device. The lookup is
722 * device managed so the reference to the backlight device is automatically
723 * dropped on driver detach.
724 *
725 * RETURNS:
726 *
727 * A pointer to the backlight device if found.
728 * Error pointer -EPROBE_DEFER if the DT property is set, but no backlight
729 * device is found. NULL if there's no backlight property.
730 */
731struct backlight_device *devm_of_find_backlight(struct device *dev)
732{
733 struct backlight_device *bd;
734 int ret;
735
736 bd = of_find_backlight(dev);
737 if (IS_ERR_OR_NULL(ptr: bd))
738 return bd;
739 ret = devm_add_action_or_reset(dev, devm_backlight_release, bd);
740 if (ret)
741 return ERR_PTR(error: ret);
742
743 return bd;
744}
745EXPORT_SYMBOL(devm_of_find_backlight);
746
747static void __exit backlight_class_exit(void)
748{
749 class_destroy(cls: backlight_class);
750}
751
752static int __init backlight_class_init(void)
753{
754 backlight_class = class_create(name: "backlight");
755 if (IS_ERR(ptr: backlight_class)) {
756 pr_warn("Unable to create backlight class; errno = %ld\n",
757 PTR_ERR(backlight_class));
758 return PTR_ERR(ptr: backlight_class);
759 }
760
761 backlight_class->dev_groups = bl_device_groups;
762 backlight_class->pm = &backlight_class_dev_pm_ops;
763 INIT_LIST_HEAD(list: &backlight_dev_list);
764 mutex_init(&backlight_dev_list_mutex);
765 BLOCKING_INIT_NOTIFIER_HEAD(&backlight_notifier);
766
767 return 0;
768}
769
770/*
771 * if this is compiled into the kernel, we need to ensure that the
772 * class is registered before users of the class try to register lcd's
773 */
774postcore_initcall(backlight_class_init);
775module_exit(backlight_class_exit);
776
777MODULE_LICENSE("GPL");
778MODULE_AUTHOR("Jamey Hicks <jamey.hicks@hp.com>, Andrew Zabolotny <zap@homelink.ru>");
779MODULE_DESCRIPTION("Backlight Lowlevel Control Abstraction");
780

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source code of linux/drivers/video/backlight/backlight.c