From b5b42b24d7830fa18537691860bd4c217f513969 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Kacper=20Piwi=C5=84ski?= Date: Mon, 7 Oct 2019 17:48:18 +0200 Subject: [PATCH] ACPI: video: update doc for acpi_video_bus_DOS() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Commit efaa14c: "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." win7: https://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/BrightnessCtrl.docx "To avoid problems that might occur if both the system firmware and the monitor driver control the brightness of the display, the display miniport driver should set bit 2 of the argument to the _DOS method. Setting this bit notifies the system firmware that it should not perform any automatic display brightness changes. The WDDM driver must set this particular bit because it controls the _DOS method. The other bits in the _DOS method control the behavior of the firmware in response to the display switch hot keys." win8: http://read.pudn.com/downloads193/doc/907411/Brightness.doc Signed-off-by: Kacper Piwiński Signed-off-by: Rafael J. Wysocki --- drivers/acpi/acpi_video.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c index 4f325e47519f..2f380e7381d6 100644 --- a/drivers/acpi/acpi_video.c +++ b/drivers/acpi/acpi_video.c @@ -699,9 +699,13 @@ acpi_video_device_EDID(struct acpi_video_device *device, * event notify code. * lcd_flag : * 0. The system BIOS should automatically control the brightness level - * of the LCD when the power changes from AC to DC + * of the LCD when: + * - the power changes from AC to DC (ACPI appendix B) + * - a brightness hotkey gets pressed (implied by Win7/8 backlight docs) * 1. The system BIOS should NOT automatically control the brightness - * level of the LCD when the power changes from AC to DC. + * level of the LCD when: + * - the power changes from AC to DC (ACPI appendix B) + * - a brightness hotkey gets pressed (implied by Win7/8 backlight docs) * Return Value: * -EINVAL wrong arg. */