+++ /dev/null
-ACPI video extensions
-~~~~~~~~~~~~~~~~~~~~~
-
-This driver implement the ACPI Extensions For Display Adapters for
-integrated graphics devices on motherboard, as specified in ACPI 2.0
-Specification, Appendix B, allowing to perform some basic control like
-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:
-
-1 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
-and set the required backlight operation structure for it for the sysfs
-interface control. For every registered class device, there will be a
-directory named acpi_videoX under /sys/class/backlight.
-
-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
-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
-
-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:
-
-Method (_BCL, 0, NotSerialized)
-{
- Return (Package (0x0C)
- {
- 0x64,
- 0x32,
- 0x0A,
- 0x14,
- 0x1E,
- 0x28,
- 0x32,
- 0x3C,
- 0x46,
- 0x50,
- 0x5A,
- 0x64
- })
-}
-
-The first two levels are for when laptop are on AC or on battery and are
-not used by Linux currently. The remaining 10 levels are supported levels
-that we can choose from. The applicable index values are from 0 (that
-corresponds to the 0x0A brightness value) to 9 (that corresponds to the
-0x64 brightness value) inclusive. Each of those index values is regarded
-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
-
-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:
-
- EV_KEY, KEY_BRIGHTNESSUP
- EV_KEY, KEY_BRIGHTNESSDOWN
- etc.
-
-For this case, ACPI video driver does not need to do anything(actually,
-it doesn't even know this happened).
-
-ii) For some laptops, the press of the hotkey will not generate the
- scancode, instead, firmware will notify the video device ACPI node
- about the event. The event value is defined in the ACPI spec. ACPI
- video driver will generate an key type input event according to 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
-
-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.
--- /dev/null
+.. 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
+Specification, Appendix B, allowing to perform some basic control like
+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.
+
+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
+and set the required backlight operation structure for it for the sysfs
+interface control. For every registered class device, there will be a
+directory named acpi_videoX under /sys/class/backlight.
+
+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
+ 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
+
+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::
+
+ Method (_BCL, 0, NotSerialized)
+ {
+ Return (Package (0x0C)
+ {
+ 0x64,
+ 0x32,
+ 0x0A,
+ 0x14,
+ 0x1E,
+ 0x28,
+ 0x32,
+ 0x3C,
+ 0x46,
+ 0x50,
+ 0x5A,
+ 0x64
+ })
+ }
+
+The first two levels are for when laptop are on AC or on battery and are
+not used by Linux currently. The remaining 10 levels are supported levels
+that we can choose from. The applicable index values are from 0 (that
+corresponds to the 0x0A brightness value) to 9 (that corresponds to the
+0x64 brightness value) inclusive. Each of those index values is regarded
+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.
+
+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::
+
+ EV_KEY, KEY_BRIGHTNESSUP
+ EV_KEY, KEY_BRIGHTNESSDOWN
+ etc.
+
+For this case, ACPI video driver does not need to do anything(actually,
+it doesn't even know this happened).
+
+ii) For some laptops, the press of the hotkey will not generate the
+ scancode, instead, firmware will notify the video device ACPI node
+ about the event. The event value is defined in the ACPI spec. ACPI
+ video driver will generate an key type input event according to 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.
+
+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.
projects / openwrt / staging / blogic.git / commitdiff