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由 Rafael J. Wysocki 提交于
According to Matthew Garrett, "Windows 8 leaves backlight control up to individual graphics drivers rather than making ACPI calls itself. There's plenty of evidence to suggest that the Intel driver for Windows [8] doesn't use the ACPI interface, including the fact that it's broken on a bunch of machines when the OS claims to support Windows 8. The simplest thing to do appears to be to disable the ACPI backlight interface on these systems". There's a problem with that approach, however, because simply avoiding to register the ACPI backlight interface if the firmware calls _OSI for Windows 8 may not work in the following situations: (1) The ACPI backlight interface actually works on the given system and the i915 driver is not loaded (e.g. another graphics driver is used). (2) The ACPI backlight interface doesn't work on the given system, but there is a vendor platform driver that will register its own, equally broken, backlight interface if not prevented from doing so by the ACPI subsystem. Therefore we need to allow the ACPI backlight interface to be registered until the i915 driver is loaded which then will unregister it if the firmware has called _OSI for Windows 8 (or will register the ACPI video driver without backlight support if not already present). For this reason, introduce an alternative function for registering ACPI video, acpi_video_register_with_quirks(), that will check whether or not the ACPI video driver has already been registered and whether or not the backlight Windows 8 quirk has to be applied. If the quirk has to be applied, it will block the ACPI backlight support and either unregister the backlight interface if the ACPI video driver has already been registered, or register the ACPI video driver without the backlight interface otherwise. Make the i915 driver use acpi_video_register_with_quirks() instead of acpi_video_register() in i915_driver_load(). This change is based on earlier patches from Matthew Garrett, Chun-Yi Lee and Seth Forshee and includes a fix from Aaron Lu's. References: https://bugzilla.kernel.org/show_bug.cgi?id=51231Tested-by: NAaron Lu <aaron.lu@intel.com> Tested-by: NIgor Gnatenko <i.gnatenko.brain@gmail.com> Tested-by: NYves-Alexis Perez <corsac@debian.org> Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com> Reviewed-by: NAaron Lu <aaron.lu@intel.com> Acked-by: NMatthew Garrett <matthew.garrett@nebula.com>
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