Documentation: ACPI: move video_extension.txt to firmware-guide/acpi and convert to reST (7fb091f8) · Commits · 戴 / test

Documentation/firmware-guide/acpi/index.rst

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		@@ -23,3 +23,4 @@ ACPI Support
		i2c-muxes
		acpi-lid
		lpit
		video_extension

Documentation/acpi/video_extension.txt→Documentation/firmware-guide/acpi/video_extension.rst

+49 −34

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		.. SPDX-License-Identifier: GPL-2.0

		=====================
		ACPI video extensions
		~~~~~~~~~~~~~~~~~~~~~
		=====================

		This driver implement the ACPI Extensions For Display Adapters for
		integrated graphics devices on motherboard, as specified in ACPI 2.0
		@@ -8,9 +11,10 @@ defining the video POST device, retrieving EDID information or to
		setup a video output, etc. Note that this is an ref. implementation
		only. It may or may not work for your integrated video device.

		The ACPI video driver does 3 things regarding backlight control:
		The ACPI video driver does 3 things regarding backlight control.

		1 Export a sysfs interface for user space to control backlight level
		Export a sysfs interface for user space to control backlight level
		==================================================================

		If the ACPI table has a video device, and acpi_backlight=vendor kernel
		command line is not present, the driver will register a backlight device
		@@ -22,17 +26,22 @@ The backlight sysfs interface has a standard definition here:
		Documentation/ABI/stable/sysfs-class-backlight.

		And what ACPI video driver does is:
		actual_brightness: on read, control method _BQC will be evaluated to

		actual_brightness:
		on read, control method _BQC will be evaluated to
		get the brightness level the firmware thinks it is at;
		bl_power: not implemented, will set the current brightness instead;
		brightness: on write, control method _BCM will run to set the requested
		brightness level;
		max_brightness: Derived from the _BCL package(see below);
		type: firmware
		bl_power:
		not implemented, will set the current brightness instead;
		brightness:
		on write, control method _BCM will run to set the requested brightness level;
		max_brightness:
		Derived from the _BCL package(see below);
		type:
		firmware

		Note that ACPI video backlight driver will always use index for
		brightness, actual_brightness and max_brightness. So if we have
		the following _BCL package:
		the following _BCL package::

		Method (_BCL, 0, NotSerialized)
		{
		@@ -62,13 +71,15 @@ as a "brightness level" indicator. Thus from the user space perspective
		the range of available brightness levels is from 0 to 9 (max_brightness)
		inclusive.

		2 Notify user space about hotkey event
		Notify user space about hotkey event
		====================================

		There are generally two cases for hotkey event reporting:

		i) For some laptops, when user presses the hotkey, a scancode will be
		generated and sent to user space through the input device created by
		the keyboard driver as a key type input event, with proper remap, the
		following key code will appear to user space:
		following key code will appear to user space::

		EV_KEY, KEY_BRIGHTNESSUP
		EV_KEY, KEY_BRIGHTNESSDOWN
		@@ -84,23 +95,27 @@ ii) For some laptops, the press of the hotkey will not generate the
		notify value it received and send the event to user space through the
		input device it created:

		===== ==================
		event keycode
		===== ==================
		0x86 KEY_BRIGHTNESSUP
		0x87 KEY_BRIGHTNESSDOWN
		etc.
		===== ==================

		so this would lead to the same effect as case i) now.

		Once user space tool receives this event, it can modify the backlight
		level through the sysfs interface.

		3 Change backlight level in the kernel
		Change backlight level in the kernel
		====================================

		This works for machines covered by case ii) in Section 2. Once the driver
		received a notification, it will set the backlight level accordingly. This does
		not affect the sending of event to user space, they are always sent to user
		space regardless of whether or not the video module controls the backlight level
		directly. This behaviour can be controlled through the brightness_switch_enabled
		module parameter as documented in admin-guide/kernel-parameters.rst. It is recommended to
		disable this behaviour once a GUI environment starts up and wants to have full
		control of the backlight level.
		module parameter as documented in admin-guide/kernel-parameters.rst. It is
		recommended to disable this behaviour once a GUI environment starts up and
		wants to have full control of the backlight level.

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