summaryrefslogtreecommitdiffstats
path: root/drivers/acpi/video_detect.c
blob: becc198e4c2242c94375ab4be8ef8aa50c07df9c (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
/*
 *  Copyright (C) 2015       Red Hat Inc.
 *                           Hans de Goede <hdegoede@redhat.com>
 *  Copyright (C) 2008       SuSE Linux Products GmbH
 *                           Thomas Renninger <trenn@suse.de>
 *
 *  May be copied or modified under the terms of the GNU General Public License
 *
 * video_detect.c:
 * After PCI devices are glued with ACPI devices
 * acpi_get_pci_dev() can be called to identify ACPI graphics
 * devices for which a real graphics card is plugged in
 *
 * Depending on whether ACPI graphics extensions (cmp. ACPI spec Appendix B)
 * are available, video.ko should be used to handle the device.
 *
 * Otherwise vendor specific drivers like thinkpad_acpi, asus-laptop,
 * sony_acpi,... can take care about backlight brightness.
 *
 * Backlight drivers can use acpi_video_get_backlight_type() to determine
 * which driver should handle the backlight.
 *
 * If CONFIG_ACPI_VIDEO is neither set as "compiled in" (y) nor as a module (m)
 * this file will not be compiled and acpi_video_get_backlight_type() will
 * always return acpi_backlight_vendor.
 */

#include <linux/export.h>
#include <linux/acpi.h>
#include <linux/backlight.h>
#include <linux/dmi.h>
#include <linux/module.h>
#include <linux/pci.h>
#include <linux/types.h>
#include <linux/workqueue.h>
#include <acpi/video.h>

void acpi_video_unregister_backlight(void);

static bool backlight_notifier_registered;
static struct notifier_block backlight_nb;
static struct work_struct backlight_notify_work;

static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;

static void acpi_video_parse_cmdline(void)
{
	if (!strcmp("vendor", acpi_video_backlight_string))
		acpi_backlight_cmdline = acpi_backlight_vendor;
	if (!strcmp("video", acpi_video_backlight_string))
		acpi_backlight_cmdline = acpi_backlight_video;
	if (!strcmp("native", acpi_video_backlight_string))
		acpi_backlight_cmdline = acpi_backlight_native;
	if (!strcmp("none", acpi_video_backlight_string))
		acpi_backlight_cmdline = acpi_backlight_none;
}

static acpi_status
find_video(acpi_handle handle, u32 lvl, void *context, void **rv)
{
	struct acpi_device *acpi_dev = acpi_fetch_acpi_dev(handle);
	long *cap = context;
	struct pci_dev *dev;

	static const struct acpi_device_id video_ids[] = {
		{ACPI_VIDEO_HID, 0},
		{"", 0},
	};

	if (acpi_dev && !acpi_match_device_ids(acpi_dev, video_ids)) {
		dev = acpi_get_pci_dev(handle);
		if (!dev)
			return AE_OK;
		pci_dev_put(dev);
		*cap |= acpi_is_video_device(handle);
	}
	return AE_OK;
}

/* Force to use vendor driver when the ACPI device is known to be
 * buggy */
static int video_detect_force_vendor(const struct dmi_system_id *d)
{
	acpi_backlight_dmi = acpi_backlight_vendor;
	return 0;
}

static int video_detect_force_video(const struct dmi_system_id *d)
{
	acpi_backlight_dmi = acpi_backlight_video;
	return 0;
}

static int video_detect_force_native(const struct dmi_system_id *d)
{
	acpi_backlight_dmi = acpi_backlight_native;
	return 0;
}

static int video_detect_force_none(const struct dmi_system_id *d)
{
	acpi_backlight_dmi = acpi_backlight_none;
	return 0;
}

static const struct dmi_system_id video_detect_dmi_table[] = {
	/* On Samsung X360, the BIOS will set a flag (VDRV) if generic
	 * ACPI backlight device is used. This flag will definitively break
	 * the backlight interface (even the vendor interface) until next
	 * reboot. It's why we should prevent video.ko from being used here
	 * and we can't rely on a later call to acpi_video_unregister().
	 */
	{
	 .callback = video_detect_force_vendor,
	 /* X360 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME, "X360"),
		DMI_MATCH(DMI_BOARD_NAME, "X360"),
		},
	},
	{
	.callback = video_detect_force_vendor,
	/* Asus UL30VT */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "UL30VT"),
		},
	},
	{
	.callback = video_detect_force_vendor,
	/* Asus UL30A */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "UL30A"),
		},
	},
	{
	.callback = video_detect_force_vendor,
	/* GIGABYTE GB-BXBT-2807 */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "GIGABYTE"),
		DMI_MATCH(DMI_PRODUCT_NAME, "GB-BXBT-2807"),
		},
	},
	{
	.callback = video_detect_force_vendor,
	/* Sony VPCEH3U1E */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
		DMI_MATCH(DMI_PRODUCT_NAME, "VPCEH3U1E"),
		},
	},
	{
	.callback = video_detect_force_vendor,
	/* Xiaomi Mi Pad 2 */
	.matches = {
			DMI_MATCH(DMI_SYS_VENDOR, "Xiaomi Inc"),
			DMI_MATCH(DMI_PRODUCT_NAME, "Mipad2"),
		},
	},

	/*
	 * These models have a working acpi_video backlight control, and using
	 * native backlight causes a regression where backlight does not work
	 * when userspace is not handling brightness key events. Disable
	 * native_backlight on these to fix this:
	 * https://bugzilla.kernel.org/show_bug.cgi?id=81691
	 */
	{
	 .callback = video_detect_force_video,
	 /* ThinkPad T420 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad T420"),
		},
	},
	{
	 .callback = video_detect_force_video,
	 /* ThinkPad T520 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad T520"),
		},
	},
	{
	 .callback = video_detect_force_video,
	 /* ThinkPad X201s */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad X201s"),
		},
	},
	{
	 .callback = video_detect_force_video,
	 /* ThinkPad X201T */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad X201T"),
		},
	},

	/* The native backlight controls do not work on some older machines */
	{
	 /* https://bugs.freedesktop.org/show_bug.cgi?id=81515 */
	 .callback = video_detect_force_video,
	 /* HP ENVY 15 Notebook */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
		DMI_MATCH(DMI_PRODUCT_NAME, "HP ENVY 15 Notebook PC"),
		},
	},
	{
	 .callback = video_detect_force_video,
	 /* SAMSUNG 870Z5E/880Z5E/680Z5E */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME, "870Z5E/880Z5E/680Z5E"),
		},
	},
	{
	 .callback = video_detect_force_video,
	 /* SAMSUNG 370R4E/370R4V/370R5E/3570RE/370R5V */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME,
			  "370R4E/370R4V/370R5E/3570RE/370R5V"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1186097 */
	 .callback = video_detect_force_video,
	 /* SAMSUNG 3570R/370R/470R/450R/510R/4450RV */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME,
			  "3570R/370R/470R/450R/510R/4450RV"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1557060 */
	 .callback = video_detect_force_video,
	 /* SAMSUNG 670Z5E */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME, "670Z5E"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1094948 */
	 .callback = video_detect_force_video,
	 /* SAMSUNG 730U3E/740U3E */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME, "730U3E/740U3E"),
		},
	},
	{
	 /* https://bugs.freedesktop.org/show_bug.cgi?id=87286 */
	 .callback = video_detect_force_video,
	 /* SAMSUNG 900X3C/900X3D/900X3E/900X4C/900X4D */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME,
			  "900X3C/900X3D/900X3E/900X4C/900X4D"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1272633 */
	 .callback = video_detect_force_video,
	 /* Dell XPS14 L421X */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "XPS L421X"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1163574 */
	 .callback = video_detect_force_video,
	 /* Dell XPS15 L521X */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "XPS L521X"),
		},
	},
	{
	 /* https://bugzilla.kernel.org/show_bug.cgi?id=108971 */
	 .callback = video_detect_force_video,
	 /* SAMSUNG 530U4E/540U4E */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
		DMI_MATCH(DMI_PRODUCT_NAME, "530U4E/540U4E"),
		},
	},
	/* https://bugs.launchpad.net/bugs/1894667 */
	{
	 .callback = video_detect_force_video,
	 /* HP 635 Notebook */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
		DMI_MATCH(DMI_PRODUCT_NAME, "HP 635 Notebook PC"),
		},
	},

	/* Non win8 machines which need native backlight nevertheless */
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1201530 */
	 .callback = video_detect_force_native,
	 /* Lenovo Ideapad S405 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_BOARD_NAME, "Lenovo IdeaPad S405"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1187004 */
	 .callback = video_detect_force_native,
	 /* Lenovo Ideapad Z570 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_NAME, "102434U"),
		},
	},
	{
	 .callback = video_detect_force_native,
	 /* Lenovo E41-25 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_NAME, "81FS"),
		},
	},
	{
	 .callback = video_detect_force_native,
	 /* Lenovo E41-45 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
		DMI_MATCH(DMI_PRODUCT_NAME, "82BK"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1217249 */
	 .callback = video_detect_force_native,
	 /* Apple MacBook Pro 12,1 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "MacBookPro12,1"),
		},
	},
	{
	 .callback = video_detect_force_native,
	 /* Dell Vostro V131 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "Vostro V131"),
		},
	},
	{
	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1123661 */
	 .callback = video_detect_force_native,
	 /* Dell XPS 17 L702X */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "Dell System XPS L702X"),
		},
	},
	{
	 .callback = video_detect_force_native,
	 /* Dell Precision 7510 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "Precision 7510"),
		},
	},
	{
	 .callback = video_detect_force_native,
	 /* Acer Aspire 5738z */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5738"),
		DMI_MATCH(DMI_BOARD_NAME, "JV50"),
		},
	},
	{
	 /* https://bugzilla.kernel.org/show_bug.cgi?id=207835 */
	 .callback = video_detect_force_native,
	 /* Acer TravelMate 5735Z */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 5735Z"),
		DMI_MATCH(DMI_BOARD_NAME, "BA51_MV"),
		},
	},
	{
	.callback = video_detect_force_native,
	/* ASUSTeK COMPUTER INC. GA401 */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
		DMI_MATCH(DMI_PRODUCT_NAME, "GA401"),
		},
	},
	{
	.callback = video_detect_force_native,
	/* ASUSTeK COMPUTER INC. GA502 */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
		DMI_MATCH(DMI_PRODUCT_NAME, "GA502"),
		},
	},
	{
	.callback = video_detect_force_native,
	/* ASUSTeK COMPUTER INC. GA503 */
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
		DMI_MATCH(DMI_PRODUCT_NAME, "GA503"),
		},
	},
	/*
	 * Clevo NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2 have both a
	 * working native and video interface. However the default detection
	 * mechanism first registers the video interface before unregistering
	 * it again and switching to the native interface during boot. This
	 * results in a dangling SBIOS request for backlight change for some
	 * reason, causing the backlight to switch to ~2% once per boot on the
	 * first power cord connect or disconnect event. Setting the native
	 * interface explicitly circumvents this buggy behaviour, by avoiding
	 * the unregistering process.
	 */
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xRU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xRU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SchenkerTechnologiesGmbH"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xRU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Notebook"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xRU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
		DMI_MATCH(DMI_BOARD_NAME, "AURA1501"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xRU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
		DMI_MATCH(DMI_BOARD_NAME, "EDUBOOK1502"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xNU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xNU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "SchenkerTechnologiesGmbH"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
		},
	},
	{
	.callback = video_detect_force_native,
	.ident = "Clevo NL5xNU",
	.matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Notebook"),
		DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
		},
	},

	/*
	 * Desktops which falsely report a backlight and which our heuristics
	 * for this do not catch.
	 */
	{
	 .callback = video_detect_force_none,
	 /* Dell OptiPlex 9020M */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 9020M"),
		},
	},
	{
	 .callback = video_detect_force_none,
	 /* MSI MS-7721 */
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "MSI"),
		DMI_MATCH(DMI_PRODUCT_NAME, "MS-7721"),
		},
	},
	{ },
};

/* This uses a workqueue to avoid various locking ordering issues */
static void acpi_video_backlight_notify_work(struct work_struct *work)
{
	if (acpi_video_get_backlight_type() != acpi_backlight_video)
		acpi_video_unregister_backlight();
}

static int acpi_video_backlight_notify(struct notifier_block *nb,
				       unsigned long val, void *bd)
{
	struct backlight_device *backlight = bd;

	/* A raw bl registering may change video -> native */
	if (backlight->props.type == BACKLIGHT_RAW &&
	    val == BACKLIGHT_REGISTERED)
		schedule_work(&backlight_notify_work);

	return NOTIFY_OK;
}

/*
 * Determine which type of backlight interface to use on this system,
 * First check cmdline, then dmi quirks, then do autodetect.
 *
 * The autodetect order is:
 * 1) Is the acpi-video backlight interface supported ->
 *  no, use a vendor interface
 * 2) Is this a win8 "ready" BIOS and do we have a native interface ->
 *  yes, use a native interface
 * 3) Else use the acpi-video interface
 *
 * Arguably the native on win8 check should be done first, but that would
 * be a behavior change, which may causes issues.
 */
enum acpi_backlight_type acpi_video_get_backlight_type(void)
{
	static DEFINE_MUTEX(init_mutex);
	static bool init_done;
	static long video_caps;

	/* Parse cmdline, dmi and acpi only once */
	mutex_lock(&init_mutex);
	if (!init_done) {
		acpi_video_parse_cmdline();
		dmi_check_system(video_detect_dmi_table);
		acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
				    ACPI_UINT32_MAX, find_video, NULL,
				    &video_caps, NULL);
		INIT_WORK(&backlight_notify_work,
			  acpi_video_backlight_notify_work);
		backlight_nb.notifier_call = acpi_video_backlight_notify;
		backlight_nb.priority = 0;
		if (backlight_register_notifier(&backlight_nb) == 0)
			backlight_notifier_registered = true;
		init_done = true;
	}
	mutex_unlock(&init_mutex);

	if (acpi_backlight_cmdline != acpi_backlight_undef)
		return acpi_backlight_cmdline;

	if (acpi_backlight_dmi != acpi_backlight_undef)
		return acpi_backlight_dmi;

	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
		return acpi_backlight_vendor;

	if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
		return acpi_backlight_native;

	return acpi_backlight_video;
}
EXPORT_SYMBOL(acpi_video_get_backlight_type);

/*
 * Set the preferred backlight interface type based on DMI info.
 * This function allows DMI blacklists to be implemented by external
 * platform drivers instead of putting a big blacklist in video_detect.c
 */
void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
{
	acpi_backlight_dmi = type;
	/* Remove acpi-video backlight interface if it is no longer desired */
	if (acpi_video_get_backlight_type() != acpi_backlight_video)
		acpi_video_unregister_backlight();
}
EXPORT_SYMBOL(acpi_video_set_dmi_backlight_type);

void __exit acpi_video_detect_exit(void)
{
	if (backlight_notifier_registered)
		backlight_unregister_notifier(&backlight_nb);
}