From efaa14c7e981bdf8d3c8d39d3ed12bdc60faabb8 Mon Sep 17 00:00:00 2001 From: Aaron Lu Date: Tue, 16 Jul 2013 13:08:05 +0800 Subject: [PATCH] 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 Reported-by: Dan Garton Reported-by: Bob Ziuchkovski Signed-off-by: Aaron Lu Signed-off-by: Rafael J. Wysocki --- drivers/acpi/video.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c index e9d4bb6..c9fa462 100644 --- a/drivers/acpi/video.c +++ b/drivers/acpi/video.c @@ -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) -- 2.7.4