linux-kernel - [PATCH 1/3] ACPI: Provide config option to disable BIOS brightness changes on power events

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Date:	Fri,  3 Feb 2012 10:18:11 -0500
From:	Matthew Garrett <mjg@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Matthew Garrett <mjg@...hat.com>, linux-acpi@...r.kernel.org,
	lenb@...nel.org
Subject: [PATCH 1/3] ACPI: Provide config option to disable BIOS brightness changes on power events

The default ACPI behaviour is to instruct the BIOS to automatically change
brightness on power events. This may be undesirable for distributions who
manage brightness in userspace. Provide a config option that disables this
behaviour and leaves brightness control up to the OS.

Signed-off-by: Matthew Garrett <mjg@...hat.com>
Cc: linux-acpi@...r.kernel.org
Cc: lenb@...nel.org
---
 drivers/acpi/Kconfig |    8 ++++++++
 drivers/acpi/video.c |    9 ++++++++-
 2 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 7556913..5354290 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -163,6 +163,14 @@ config ACPI_VIDEO
 	  To compile this driver as a module, choose M here:
 	  the module will be called video.
 
+config ACPI_VIDEO_DISABLE_BIOS_POWER_BRIGHTNESS
+        bool "Disable BIOS brightness changes on power events"
+        depends on ACPI_VIDEO
+        default n
+        help
+	  Many laptops will automatically change brightness on AC/battery
+	  status changes. Choose Y here to disable this.
+
 config ACPI_FAN
 	tristate "Fan"
 	select THERMAL
diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index eaef02a..4b42938 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -86,6 +86,13 @@ module_param(allow_duplicates, bool, 0644);
 static bool use_bios_initial_backlight = 1;
 module_param(use_bios_initial_backlight, bool, 0644);
 
+#ifdef CONFIG_ACPI_VIDEO_DISABLE_BIOS_POWER_BRIGHTNESS
+static bool disable_bios_power_change = true;
+#else
+static bool disable_bios_power_change;
+#endif
+module_param(disable_bios_power_change, bool, 0644);
+
 static int register_count = 0;
 static int acpi_video_bus_add(struct acpi_device *device);
 static int acpi_video_bus_remove(struct acpi_device *device, int type);
@@ -1421,7 +1428,7 @@ static int acpi_video_bus_put_devices(struct acpi_video_bus *video)
 
 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, disable_bios_power_change);
 }
 
 static int acpi_video_bus_stop_devices(struct acpi_video_bus *video)
-- 
1.7.7.6

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