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 
66 static struct list_head backlight_dev_list;
67 static struct mutex backlight_dev_list_mutex;
68 static struct blocking_notifier_head backlight_notifier;
69 
70 static const char *const backlight_types[] = {
71 	[BACKLIGHT_RAW] = "raw",
72 	[BACKLIGHT_PLATFORM] = "platform",
73 	[BACKLIGHT_FIRMWARE] = "firmware",
74 };
75 
76 static 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) || (defined(CONFIG_FB_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  */
96 static 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 	}
132 out:
133 	mutex_unlock(&bd->ops_lock);
134 	return 0;
135 }
136 
137 static 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(&bd->fb_notif);
143 }
144 
145 static void backlight_unregister_fb(struct backlight_device *bd)
146 {
147 	fb_unregister_client(&bd->fb_notif);
148 }
149 #else
150 static inline int backlight_register_fb(struct backlight_device *bd)
151 {
152 	return 0;
153 }
154 
155 static inline void backlight_unregister_fb(struct backlight_device *bd)
156 {
157 }
158 #endif /* CONFIG_FB */
159 
160 static 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(&bd->dev.kobj, KOBJ_CHANGE, envp);
178 	sysfs_notify(&bd->dev.kobj, NULL, "actual_brightness");
179 }
180 
181 static 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, "%d\n", bd->props.power);
187 }
188 
189 static 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(buf, 0, &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(&bd->ops_lock);
217 
218 	return rc;
219 }
220 static DEVICE_ATTR_RW(bl_power);
221 
222 static 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, "%d\n", bd->props.brightness);
228 }
229 
230 int 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(&bd->ops_lock);
246 
247 	backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
248 
249 	return rc;
250 }
251 EXPORT_SYMBOL(backlight_device_set_brightness);
252 
253 static 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(buf, 0, &brightness);
261 	if (rc)
262 		return rc;
263 
264 	rc = backlight_device_set_brightness(bd, brightness);
265 
266 	return rc ? rc : count;
267 }
268 static DEVICE_ATTR_RW(brightness);
269 
270 static 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, "%s\n", backlight_types[bd->props.type]);
276 }
277 static DEVICE_ATTR_RO(type);
278 
279 static 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, "%d\n", bd->props.max_brightness);
285 }
286 static DEVICE_ATTR_RO(max_brightness);
287 
288 static 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, "%d\n", rc);
299 	} else {
300 		rc = sprintf(buf, "%d\n", bd->props.brightness);
301 	}
302 	mutex_unlock(&bd->ops_lock);
303 
304 	return rc;
305 }
306 static DEVICE_ATTR_RO(actual_brightness);
307 
308 static 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, "unknown\n");
315 
316 	return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]);
317 }
318 static DEVICE_ATTR_RO(scale);
319 
320 static struct class *backlight_class;
321 
322 #ifdef CONFIG_PM_SLEEP
323 static 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(&bd->ops_lock);
333 
334 	return 0;
335 }
336 
337 static 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(&bd->ops_lock);
347 
348 	return 0;
349 }
350 #endif
351 
352 static SIMPLE_DEV_PM_OPS(backlight_class_dev_pm_ops, backlight_suspend,
353 			 backlight_resume);
354 
355 static void bl_device_release(struct device *dev)
356 {
357 	struct backlight_device *bd = to_backlight_device(dev);
358 	kfree(bd);
359 }
360 
361 static 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 };
370 ATTRIBUTE_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  */
384 void 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(&bd->ops_lock);
400 	backlight_generate_event(bd, reason);
401 }
402 EXPORT_SYMBOL(backlight_force_update);
403 
404 /* deprecated - use devm_backlight_device_register() */
405 struct 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(sizeof(struct backlight_device), GFP_KERNEL);
415 	if (!new_bd)
416 		return ERR_PTR(-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(&new_bd->dev, "%s", name);
425 	dev_set_drvdata(&new_bd->dev, 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(&new_bd->dev);
440 	if (rc) {
441 		put_device(&new_bd->dev);
442 		return ERR_PTR(rc);
443 	}
444 
445 	rc = backlight_register_fb(new_bd);
446 	if (rc) {
447 		device_unregister(&new_bd->dev);
448 		return ERR_PTR(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_bd->entry, &backlight_dev_list);
462 	mutex_unlock(&backlight_dev_list_mutex);
463 
464 	blocking_notifier_call_chain(&backlight_notifier,
465 				     BACKLIGHT_REGISTERED, new_bd);
466 
467 	return new_bd;
468 }
469 EXPORT_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  */
480 struct 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(&backlight_dev_list_mutex);
493 
494 	return found ? bd : NULL;
495 }
496 EXPORT_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 backlight_put().
505  *
506  * Returns:
507  * A pointer to the backlight device if found, otherwise NULL.
508  */
509 struct backlight_device *backlight_device_get_by_name(const char *name)
510 {
511 	struct device *dev;
512 
513 	dev = class_find_device_by_name(backlight_class, name);
514 
515 	return dev ? to_backlight_device(dev) : NULL;
516 }
517 EXPORT_SYMBOL(backlight_device_get_by_name);
518 
519 /* deprecated - use devm_backlight_device_unregister() */
520 void backlight_device_unregister(struct backlight_device *bd)
521 {
522 	if (!bd)
523 		return;
524 
525 	mutex_lock(&backlight_dev_list_mutex);
526 	list_del(&bd->entry);
527 	mutex_unlock(&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(&backlight_notifier,
537 				     BACKLIGHT_UNREGISTERED, bd);
538 
539 	mutex_lock(&bd->ops_lock);
540 	bd->ops = NULL;
541 	mutex_unlock(&bd->ops_lock);
542 
543 	backlight_unregister_fb(bd);
544 	device_unregister(&bd->dev);
545 }
546 EXPORT_SYMBOL(backlight_device_unregister);
547 
548 static 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 
555 static 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  */
574 int backlight_register_notifier(struct notifier_block *nb)
575 {
576 	return blocking_notifier_chain_register(&backlight_notifier, nb);
577 }
578 EXPORT_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  */
591 int backlight_unregister_notifier(struct notifier_block *nb)
592 {
593 	return blocking_notifier_chain_unregister(&backlight_notifier, nb);
594 }
595 EXPORT_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  */
614 struct 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(-ENOMEM);
625 
626 	backlight = backlight_device_register(name, parent, devdata, ops,
627 						props);
628 	if (!IS_ERR(backlight)) {
629 		*ptr = backlight;
630 		devres_add(dev, ptr);
631 	} else {
632 		devres_free(ptr);
633 	}
634 
635 	return backlight;
636 }
637 EXPORT_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  */
648 void devm_backlight_device_unregister(struct device *dev,
649 				struct backlight_device *bd)
650 {
651 	int rc;
652 
653 	rc = devres_release(dev, devm_backlight_device_release,
654 				devm_backlight_device_match, bd);
655 	WARN_ON(rc);
656 }
657 EXPORT_SYMBOL(devm_backlight_device_unregister);
658 
659 #ifdef CONFIG_OF
660 static 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  */
677 struct backlight_device *of_find_backlight_by_node(struct device_node *node)
678 {
679 	struct device *dev;
680 
681 	dev = class_find_device(backlight_class, NULL, node, of_parent_match);
682 
683 	return dev ? to_backlight_device(dev) : NULL;
684 }
685 EXPORT_SYMBOL(of_find_backlight_by_node);
686 #endif
687 
688 static 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(dev->of_node, "backlight", 0);
698 		if (np) {
699 			bd = of_find_backlight_by_node(np);
700 			of_node_put(np);
701 			if (!bd)
702 				return ERR_PTR(-EPROBE_DEFER);
703 		}
704 	}
705 
706 	return bd;
707 }
708 
709 static void devm_backlight_release(void *data)
710 {
711 	struct backlight_device *bd = data;
712 
713 	put_device(&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  */
731 struct 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(bd))
738 		return bd;
739 	ret = devm_add_action_or_reset(dev, devm_backlight_release, bd);
740 	if (ret)
741 		return ERR_PTR(ret);
742 
743 	return bd;
744 }
745 EXPORT_SYMBOL(devm_of_find_backlight);
746 
747 static void __exit backlight_class_exit(void)
748 {
749 	class_destroy(backlight_class);
750 }
751 
752 static int __init backlight_class_init(void)
753 {
754 	backlight_class = class_create(THIS_MODULE, "backlight");
755 	if (IS_ERR(backlight_class)) {
756 		pr_warn("Unable to create backlight class; errno = %ld\n",
757 			PTR_ERR(backlight_class));
758 		return PTR_ERR(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(&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  */
774 postcore_initcall(backlight_class_init);
775 module_exit(backlight_class_exit);
776 
777 MODULE_LICENSE("GPL");
778 MODULE_AUTHOR("Jamey Hicks <jamey.hicks@hp.com>, Andrew Zabolotny <zap@homelink.ru>");
779 MODULE_DESCRIPTION("Backlight Lowlevel Control Abstraction");
780