Re: [PATCH] acpi: video: no automatic brightness changes by firmware

[Aaron Lu <aaron.lu@intel.com>]

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

Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=52951
Buglink: 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>
---
Apply on top of:
https://patchwork.kernel.org/patch/2812951/ (expose OSI version)
https://patchwork.kernel.org/patch/2827793/ (win8 video quirk)

Micael, Dan and Bob,
Please give the patch a test if possible, thanks.

v2: Make the behavior change only for win8 systems; use the newly added
    function acpi_video_backlight_quirks as the condition check for win8.

 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 01b1a25..bc2954b 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -1534,14 +1534,20 @@ 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)
--
1.8.3.2.10.g43d11f4