Commit efaa14c7 authored Jul 16, 2013 by Aaron Lu Committed by Rafael J. Wysocki Jul 18, 2013

ACPI / video: no automatic brightness changes by win8-compatible firmware

Starting from win8, MS backlight control driver will set bit 2 of the
parameter of control method _DOS, to inform firmware it should not
perform any automatic brightness changes. This mostly affects hotkey
notification deliver - if we do not set this bit, on hotkey press,
firmware may choose to adjust brightness level instead of sending out
notification and doing nothing.

So this patch sets bit 2 when calling _DOS so that GUIs can show the
notification window on hotkey press.  This behavior change is only
necessary for win8 systems.

The MS document on win8 backlight control is here:
http://msdn.microsoft.com/en-US/library/windows/hardware/jj159305

References: https://bugzilla.kernel.org/show_bug.cgi?id=52951
References: https://bugzilla.kernel.org/show_bug.cgi?id=56711


Reported-by: Micael Dias <kam1kaz3@gmail.com>
Reported-by: Dan Garton <dan.garton@gmail.com>
Reported-by: Bob Ziuchkovski <bob.ziuchkovski@gmail.com>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent 8c5bd7ad

drivers/acpi/video.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1539,14 +1539,20 @@ static int acpi_video_bus_put_devices(struct acpi_video_bus *video)

		/* acpi_video interface */

		/*
		* Win8 requires setting bit2 of _DOS to let firmware know it shouldn't
		* preform any automatic brightness change on receiving a notification.
		*/
		static int acpi_video_bus_start_devices(struct acpi_video_bus *video)
		{
		return acpi_video_bus_DOS(video, 0, 0);
		return acpi_video_bus_DOS(video, 0,
		acpi_video_backlight_quirks() ? 1 : 0);
		}

		static int acpi_video_bus_stop_devices(struct acpi_video_bus *video)
		{
		return acpi_video_bus_DOS(video, 0, 1);
		return acpi_video_bus_DOS(video, 0,
		acpi_video_backlight_quirks() ? 0 : 1);
		}

		static void acpi_video_bus_notify(struct acpi_device *device, u32 event)

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