drivers/acpi/video_detect.c

   1 /*
   2  *  Copyright (C) 2015       Red Hat Inc.
   3  *                           Hans de Goede <hdegoede@redhat.com>
   4  *  Copyright (C) 2008       SuSE Linux Products GmbH
   5  *                           Thomas Renninger <trenn@suse.de>
   6  *
   7  *  May be copied or modified under the terms of the GNU General Public License
   8  *
   9  * video_detect.c:
  10  * After PCI devices are glued with ACPI devices
  11  * acpi_get_pci_dev() can be called to identify ACPI graphics
  12  * devices for which a real graphics card is plugged in
  13  *
  14  * Depending on whether ACPI graphics extensions (cmp. ACPI spec Appendix B)
  15  * are available, video.ko should be used to handle the device.
  16  *
  17  * Otherwise vendor specific drivers like thinkpad_acpi, asus-laptop,
  18  * sony_acpi,... can take care about backlight brightness.
  19  *
  20  * Backlight drivers can use acpi_video_get_backlight_type() to determine
  21  * which driver should handle the backlight.
  22  *
  23  * If CONFIG_ACPI_VIDEO is neither set as "compiled in" (y) nor as a module (m)
  24  * this file will not be compiled and acpi_video_get_backlight_type() will
  25  * always return acpi_backlight_vendor.
  26  */
  27
  28 #include <linux/export.h>
  29 #include <linux/acpi.h>
  30 #include <linux/backlight.h>
  31 #include <linux/dmi.h>
  32 #include <linux/module.h>
  33 #include <linux/pci.h>
  34 #include <linux/types.h>
  35 #include <linux/workqueue.h>
  36 #include <acpi/video.h>
  37
  38 void acpi_video_unregister_backlight(void);
  39
  40 static bool backlight_notifier_registered;
  41 static struct notifier_block backlight_nb;
  42 static struct work_struct backlight_notify_work;
  43
  44 static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
  45 static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;
  46
  47 static void acpi_video_parse_cmdline(void)
  48 {
  49         if (!strcmp("vendor", acpi_video_backlight_string))
  50                 acpi_backlight_cmdline = acpi_backlight_vendor;
  51         if (!strcmp("video", acpi_video_backlight_string))
  52                 acpi_backlight_cmdline = acpi_backlight_video;
  53         if (!strcmp("native", acpi_video_backlight_string))
  54                 acpi_backlight_cmdline = acpi_backlight_native;
  55         if (!strcmp("none", acpi_video_backlight_string))
  56                 acpi_backlight_cmdline = acpi_backlight_none;
  57 }
  58
  59 static acpi_status
  60 find_video(acpi_handle handle, u32 lvl, void *context, void **rv)
  61 {
  62         struct acpi_device *acpi_dev = acpi_fetch_acpi_dev(handle);
  63         long *cap = context;
  64         struct pci_dev *dev;
  65
  66         static const struct acpi_device_id video_ids[] = {
  67                 {ACPI_VIDEO_HID, 0},
  68                 {"", 0},
  69         };
  70
  71         if (acpi_dev && !acpi_match_device_ids(acpi_dev, video_ids)) {
  72                 dev = acpi_get_pci_dev(handle);
  73                 if (!dev)
  74                         return AE_OK;
  75                 pci_dev_put(dev);
  76                 *cap |= acpi_is_video_device(handle);
  77         }
  78         return AE_OK;
  79 }
  80
  81 /* Force to use vendor driver when the ACPI device is known to be
  82  * buggy */
  83 static int video_detect_force_vendor(const struct dmi_system_id *d)
  84 {
  85         acpi_backlight_dmi = acpi_backlight_vendor;
  86         return 0;
  87 }
  88
  89 static int video_detect_force_video(const struct dmi_system_id *d)
  90 {
  91         acpi_backlight_dmi = acpi_backlight_video;
  92         return 0;
  93 }
  94
  95 static int video_detect_force_native(const struct dmi_system_id *d)
  96 {
  97         acpi_backlight_dmi = acpi_backlight_native;
  98         return 0;
  99 }
 100
 101 static int video_detect_force_none(const struct dmi_system_id *d)
 102 {
 103         acpi_backlight_dmi = acpi_backlight_none;
 104         return 0;
 105 }
 106
 107 static const struct dmi_system_id video_detect_dmi_table[] = {
 108         /* On Samsung X360, the BIOS will set a flag (VDRV) if generic
 109          * ACPI backlight device is used. This flag will definitively break
 110          * the backlight interface (even the vendor interface) until next
 111          * reboot. It's why we should prevent video.ko from being used here
 112          * and we can't rely on a later call to acpi_video_unregister().
 113          */
 114         {
 115          .callback = video_detect_force_vendor,
 116          /* X360 */
 117          .matches = {
 118                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 119                 DMI_MATCH(DMI_PRODUCT_NAME, "X360"),
 120                 DMI_MATCH(DMI_BOARD_NAME, "X360"),
 121                 },
 122         },
 123         {
 124         .callback = video_detect_force_vendor,
 125         /* Asus UL30VT */
 126         .matches = {
 127                 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
 128                 DMI_MATCH(DMI_PRODUCT_NAME, "UL30VT"),
 129                 },
 130         },
 131         {
 132         .callback = video_detect_force_vendor,
 133         /* Asus UL30A */
 134         .matches = {
 135                 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
 136                 DMI_MATCH(DMI_PRODUCT_NAME, "UL30A"),
 137                 },
 138         },
 139         {
 140         .callback = video_detect_force_vendor,
 141         /* GIGABYTE GB-BXBT-2807 */
 142         .matches = {
 143                 DMI_MATCH(DMI_SYS_VENDOR, "GIGABYTE"),
 144                 DMI_MATCH(DMI_PRODUCT_NAME, "GB-BXBT-2807"),
 145                 },
 146         },
 147         {
 148         .callback = video_detect_force_vendor,
 149         /* Sony VPCEH3U1E */
 150         .matches = {
 151                 DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
 152                 DMI_MATCH(DMI_PRODUCT_NAME, "VPCEH3U1E"),
 153                 },
 154         },
 155         {
 156         .callback = video_detect_force_vendor,
 157         /* Xiaomi Mi Pad 2 */
 158         .matches = {
 159                         DMI_MATCH(DMI_SYS_VENDOR, "Xiaomi Inc"),
 160                         DMI_MATCH(DMI_PRODUCT_NAME, "Mipad2"),
 161                 },
 162         },
 163
 164         /*
 165          * These models have a working acpi_video backlight control, and using
 166          * native backlight causes a regression where backlight does not work
 167          * when userspace is not handling brightness key events. Disable
 168          * native_backlight on these to fix this:
 169          * https://bugzilla.kernel.org/show_bug.cgi?id=81691
 170          */
 171         {
 172          .callback = video_detect_force_video,
 173          /* ThinkPad T420 */
 174          .matches = {
 175                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 176                 DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad T420"),
 177                 },
 178         },
 179         {
 180          .callback = video_detect_force_video,
 181          /* ThinkPad T520 */
 182          .matches = {
 183                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 184                 DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad T520"),
 185                 },
 186         },
 187         {
 188          .callback = video_detect_force_video,
 189          /* ThinkPad X201s */
 190          .matches = {
 191                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 192                 DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad X201s"),
 193                 },
 194         },
 195         {
 196          .callback = video_detect_force_video,
 197          /* ThinkPad X201T */
 198          .matches = {
 199                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 200                 DMI_MATCH(DMI_PRODUCT_VERSION, "ThinkPad X201T"),
 201                 },
 202         },
 203
 204         /* The native backlight controls do not work on some older machines */
 205         {
 206          /* https://bugs.freedesktop.org/show_bug.cgi?id=81515 */
 207          .callback = video_detect_force_video,
 208          /* HP ENVY 15 Notebook */
 209          .matches = {
 210                 DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
 211                 DMI_MATCH(DMI_PRODUCT_NAME, "HP ENVY 15 Notebook PC"),
 212                 },
 213         },
 214         {
 215          .callback = video_detect_force_video,
 216          /* SAMSUNG 870Z5E/880Z5E/680Z5E */
 217          .matches = {
 218                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 219                 DMI_MATCH(DMI_PRODUCT_NAME, "870Z5E/880Z5E/680Z5E"),
 220                 },
 221         },
 222         {
 223          .callback = video_detect_force_video,
 224          /* SAMSUNG 370R4E/370R4V/370R5E/3570RE/370R5V */
 225          .matches = {
 226                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 227                 DMI_MATCH(DMI_PRODUCT_NAME,
 228                           "370R4E/370R4V/370R5E/3570RE/370R5V"),
 229                 },
 230         },
 231         {
 232          /* https://bugzilla.redhat.com/show_bug.cgi?id=1186097 */
 233          .callback = video_detect_force_video,
 234          /* SAMSUNG 3570R/370R/470R/450R/510R/4450RV */
 235          .matches = {
 236                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 237                 DMI_MATCH(DMI_PRODUCT_NAME,
 238                           "3570R/370R/470R/450R/510R/4450RV"),
 239                 },
 240         },
 241         {
 242          /* https://bugzilla.redhat.com/show_bug.cgi?id=1557060 */
 243          .callback = video_detect_force_video,
 244          /* SAMSUNG 670Z5E */
 245          .matches = {
 246                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 247                 DMI_MATCH(DMI_PRODUCT_NAME, "670Z5E"),
 248                 },
 249         },
 250         {
 251          /* https://bugzilla.redhat.com/show_bug.cgi?id=1094948 */
 252          .callback = video_detect_force_video,
 253          /* SAMSUNG 730U3E/740U3E */
 254          .matches = {
 255                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 256                 DMI_MATCH(DMI_PRODUCT_NAME, "730U3E/740U3E"),
 257                 },
 258         },
 259         {
 260          /* https://bugs.freedesktop.org/show_bug.cgi?id=87286 */
 261          .callback = video_detect_force_video,
 262          /* SAMSUNG 900X3C/900X3D/900X3E/900X4C/900X4D */
 263          .matches = {
 264                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 265                 DMI_MATCH(DMI_PRODUCT_NAME,
 266                           "900X3C/900X3D/900X3E/900X4C/900X4D"),
 267                 },
 268         },
 269         {
 270          /* https://bugzilla.redhat.com/show_bug.cgi?id=1272633 */
 271          .callback = video_detect_force_video,
 272          /* Dell XPS14 L421X */
 273          .matches = {
 274                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 275                 DMI_MATCH(DMI_PRODUCT_NAME, "XPS L421X"),
 276                 },
 277         },
 278         {
 279          /* https://bugzilla.redhat.com/show_bug.cgi?id=1163574 */
 280          .callback = video_detect_force_video,
 281          /* Dell XPS15 L521X */
 282          .matches = {
 283                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 284                 DMI_MATCH(DMI_PRODUCT_NAME, "XPS L521X"),
 285                 },
 286         },
 287         {
 288          /* https://bugzilla.kernel.org/show_bug.cgi?id=108971 */
 289          .callback = video_detect_force_video,
 290          /* SAMSUNG 530U4E/540U4E */
 291          .matches = {
 292                 DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
 293                 DMI_MATCH(DMI_PRODUCT_NAME, "530U4E/540U4E"),
 294                 },
 295         },
 296         /* https://bugs.launchpad.net/bugs/1894667 */
 297         {
 298          .callback = video_detect_force_video,
 299          /* HP 635 Notebook */
 300          .matches = {
 301                 DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
 302                 DMI_MATCH(DMI_PRODUCT_NAME, "HP 635 Notebook PC"),
 303                 },
 304         },
 305
 306         /* Non win8 machines which need native backlight nevertheless */
 307         {
 308          /* https://bugzilla.redhat.com/show_bug.cgi?id=1201530 */
 309          .callback = video_detect_force_native,
 310          /* Lenovo Ideapad S405 */
 311          .matches = {
 312                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 313                 DMI_MATCH(DMI_BOARD_NAME, "Lenovo IdeaPad S405"),
 314                 },
 315         },
 316         {
 317          /* https://bugzilla.redhat.com/show_bug.cgi?id=1187004 */
 318          .callback = video_detect_force_native,
 319          /* Lenovo Ideapad Z570 */
 320          .matches = {
 321                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 322                 DMI_MATCH(DMI_PRODUCT_NAME, "102434U"),
 323                 },
 324         },
 325         {
 326          .callback = video_detect_force_native,
 327          /* Lenovo E41-25 */
 328          .matches = {
 329                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 330                 DMI_MATCH(DMI_PRODUCT_NAME, "81FS"),
 331                 },
 332         },
 333         {
 334          .callback = video_detect_force_native,
 335          /* Lenovo E41-45 */
 336          .matches = {
 337                 DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
 338                 DMI_MATCH(DMI_PRODUCT_NAME, "82BK"),
 339                 },
 340         },
 341         {
 342          /* https://bugzilla.redhat.com/show_bug.cgi?id=1217249 */
 343          .callback = video_detect_force_native,
 344          /* Apple MacBook Pro 12,1 */
 345          .matches = {
 346                 DMI_MATCH(DMI_SYS_VENDOR, "Apple Inc."),
 347                 DMI_MATCH(DMI_PRODUCT_NAME, "MacBookPro12,1"),
 348                 },
 349         },
 350         {
 351          .callback = video_detect_force_native,
 352          /* Dell Vostro V131 */
 353          .matches = {
 354                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 355                 DMI_MATCH(DMI_PRODUCT_NAME, "Vostro V131"),
 356                 },
 357         },
 358         {
 359          /* https://bugzilla.redhat.com/show_bug.cgi?id=1123661 */
 360          .callback = video_detect_force_native,
 361          /* Dell XPS 17 L702X */
 362          .matches = {
 363                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 364                 DMI_MATCH(DMI_PRODUCT_NAME, "Dell System XPS L702X"),
 365                 },
 366         },
 367         {
 368          .callback = video_detect_force_native,
 369          /* Dell Precision 7510 */
 370          .matches = {
 371                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 372                 DMI_MATCH(DMI_PRODUCT_NAME, "Precision 7510"),
 373                 },
 374         },
 375         {
 376          .callback = video_detect_force_native,
 377          /* Acer Aspire 5738z */
 378          .matches = {
 379                 DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
 380                 DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5738"),
 381                 DMI_MATCH(DMI_BOARD_NAME, "JV50"),
 382                 },
 383         },
 384         {
 385          /* https://bugzilla.kernel.org/show_bug.cgi?id=207835 */
 386          .callback = video_detect_force_native,
 387          /* Acer TravelMate 5735Z */
 388          .matches = {
 389                 DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
 390                 DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 5735Z"),
 391                 DMI_MATCH(DMI_BOARD_NAME, "BA51_MV"),
 392                 },
 393         },
 394         {
 395         .callback = video_detect_force_native,
 396         /* ASUSTeK COMPUTER INC. GA401 */
 397         .matches = {
 398                 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 399                 DMI_MATCH(DMI_PRODUCT_NAME, "GA401"),
 400                 },
 401         },
 402         {
 403         .callback = video_detect_force_native,
 404         /* ASUSTeK COMPUTER INC. GA502 */
 405         .matches = {
 406                 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 407                 DMI_MATCH(DMI_PRODUCT_NAME, "GA502"),
 408                 },
 409         },
 410         {
 411         .callback = video_detect_force_native,
 412         /* ASUSTeK COMPUTER INC. GA503 */
 413         .matches = {
 414                 DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 415                 DMI_MATCH(DMI_PRODUCT_NAME, "GA503"),
 416                 },
 417         },
 418         /*
 419          * Clevo NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2 have both a
 420          * working native and video interface. However the default detection
 421          * mechanism first registers the video interface before unregistering
 422          * it again and switching to the native interface during boot. This
 423          * results in a dangling SBIOS request for backlight change for some
 424          * reason, causing the backlight to switch to ~2% once per boot on the
 425          * first power cord connect or disconnect event. Setting the native
 426          * interface explicitly circumvents this buggy behaviour, by avoiding
 427          * the unregistering process.
 428          */
 429         {
 430         .callback = video_detect_force_native,
 431         .ident = "Clevo NL5xRU",
 432         .matches = {
 433                 DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
 434                 DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
 435                 },
 436         },
 437         {
 438         .callback = video_detect_force_native,
 439         .ident = "Clevo NL5xRU",
 440         .matches = {
 441                 DMI_MATCH(DMI_SYS_VENDOR, "SchenkerTechnologiesGmbH"),
 442                 DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
 443                 },
 444         },
 445         {
 446         .callback = video_detect_force_native,
 447         .ident = "Clevo NL5xRU",
 448         .matches = {
 449                 DMI_MATCH(DMI_SYS_VENDOR, "Notebook"),
 450                 DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
 451                 },
 452         },
 453         {
 454         .callback = video_detect_force_native,
 455         .ident = "Clevo NL5xRU",
 456         .matches = {
 457                 DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
 458                 DMI_MATCH(DMI_BOARD_NAME, "AURA1501"),
 459                 },
 460         },
 461         {
 462         .callback = video_detect_force_native,
 463         .ident = "Clevo NL5xRU",
 464         .matches = {
 465                 DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
 466                 DMI_MATCH(DMI_BOARD_NAME, "EDUBOOK1502"),
 467                 },
 468         },
 469         {
 470         .callback = video_detect_force_native,
 471         .ident = "Clevo NL5xNU",
 472         .matches = {
 473                 DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
 474                 DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
 475                 },
 476         },
 477         {
 478         .callback = video_detect_force_native,
 479         .ident = "Clevo NL5xNU",
 480         .matches = {
 481                 DMI_MATCH(DMI_SYS_VENDOR, "SchenkerTechnologiesGmbH"),
 482                 DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
 483                 },
 484         },
 485         {
 486         .callback = video_detect_force_native,
 487         .ident = "Clevo NL5xNU",
 488         .matches = {
 489                 DMI_MATCH(DMI_SYS_VENDOR, "Notebook"),
 490                 DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
 491                 },
 492         },
 493
 494         /*
 495          * Desktops which falsely report a backlight and which our heuristics
 496          * for this do not catch.
 497          */
 498         {
 499          .callback = video_detect_force_none,
 500          /* Dell OptiPlex 9020M */
 501          .matches = {
 502                 DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
 503                 DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 9020M"),
 504                 },
 505         },
 506         {
 507          .callback = video_detect_force_none,
 508          /* MSI MS-7721 */
 509          .matches = {
 510                 DMI_MATCH(DMI_SYS_VENDOR, "MSI"),
 511                 DMI_MATCH(DMI_PRODUCT_NAME, "MS-7721"),
 512                 },
 513         },
 514         { },
 515 };
 516
 517 /* This uses a workqueue to avoid various locking ordering issues */
 518 static void acpi_video_backlight_notify_work(struct work_struct *work)
 519 {
 520         if (acpi_video_get_backlight_type() != acpi_backlight_video)
 521                 acpi_video_unregister_backlight();
 522 }
 523
 524 static int acpi_video_backlight_notify(struct notifier_block *nb,
 525                                        unsigned long val, void *bd)
 526 {
 527         struct backlight_device *backlight = bd;
 528
 529         /* A raw bl registering may change video -> native */
 530         if (backlight->props.type == BACKLIGHT_RAW &&
 531             val == BACKLIGHT_REGISTERED)
 532                 schedule_work(&backlight_notify_work);
 533
 534         return NOTIFY_OK;
 535 }
 536
 537 /*
 538  * Determine which type of backlight interface to use on this system,
 539  * First check cmdline, then dmi quirks, then do autodetect.
 540  *
 541  * The autodetect order is:
 542  * 1) Is the acpi-video backlight interface supported ->
 543  *  no, use a vendor interface
 544  * 2) Is this a win8 "ready" BIOS and do we have a native interface ->
 545  *  yes, use a native interface
 546  * 3) Else use the acpi-video interface
 547  *
 548  * Arguably the native on win8 check should be done first, but that would
 549  * be a behavior change, which may causes issues.
 550  */
 551 enum acpi_backlight_type acpi_video_get_backlight_type(void)
 552 {
 553         static DEFINE_MUTEX(init_mutex);
 554         static bool init_done;
 555         static long video_caps;
 556
 557         /* Parse cmdline, dmi and acpi only once */
 558         mutex_lock(&init_mutex);
 559         if (!init_done) {
 560                 acpi_video_parse_cmdline();
 561                 dmi_check_system(video_detect_dmi_table);
 562                 acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
 563                                     ACPI_UINT32_MAX, find_video, NULL,
 564                                     &video_caps, NULL);
 565                 INIT_WORK(&backlight_notify_work,
 566                           acpi_video_backlight_notify_work);
 567                 backlight_nb.notifier_call = acpi_video_backlight_notify;
 568                 backlight_nb.priority = 0;
 569                 if (backlight_register_notifier(&backlight_nb) == 0)
 570                         backlight_notifier_registered = true;
 571                 init_done = true;
 572         }
 573         mutex_unlock(&init_mutex);
 574
 575         if (acpi_backlight_cmdline != acpi_backlight_undef)
 576                 return acpi_backlight_cmdline;
 577
 578         if (acpi_backlight_dmi != acpi_backlight_undef)
 579                 return acpi_backlight_dmi;
 580
 581         if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
 582                 return acpi_backlight_vendor;
 583
 584         if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
 585                 return acpi_backlight_native;
 586
 587         return acpi_backlight_video;
 588 }
 589 EXPORT_SYMBOL(acpi_video_get_backlight_type);
 590
 591 /*
 592  * Set the preferred backlight interface type based on DMI info.
 593  * This function allows DMI blacklists to be implemented by external
 594  * platform drivers instead of putting a big blacklist in video_detect.c
 595  */
 596 void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
 597 {
 598         acpi_backlight_dmi = type;
 599         /* Remove acpi-video backlight interface if it is no longer desired */
 600         if (acpi_video_get_backlight_type() != acpi_backlight_video)
 601                 acpi_video_unregister_backlight();
 602 }
 603 EXPORT_SYMBOL(acpi_video_set_dmi_backlight_type);
 604
 605 void __exit acpi_video_detect_exit(void)
 606 {
 607         if (backlight_notifier_registered)
 608                 backlight_unregister_notifier(&backlight_nb);
 609 }