[PATCH v6 24/24] Documentation: ACPI: move video_extension.txt to firmware-guide/acpi and convert to reST

Changbin Du
2019-04-25T15:31:17Z

.../acpi/video_extension.rst} | 85 +++++++++++--------
2 files changed, 52 insertions(+), 34 deletions(-)
rename Documentation/{acpi/video_extension.txt => firmware-guide/acpi/video_extension.rst} (68%)

diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
index 0e60f4b7129a..ae609eec4679 100644
--- a/Documentation/firmware-guide/acpi/index.rst
+++ b/Documentation/firmware-guide/acpi/index.rst
@@ -23,3 +23,4 @@ ACPI Support
i2c-muxes
acpi-lid
lpit
+ video_extension
diff --git a/Documentation/acpi/video_extension.txt b/Documentation/firmware-guide/acpi/video_extension.rst
similarity index 68%
rename from Documentation/acpi/video_extension.txt
rename to Documentation/firmware-guide/acpi/video_extension.rst
index 79bf6a4921be..932fb47342a7 100644
--- a/Documentation/acpi/video_extension.txt
+++ b/Documentation/firmware-guide/acpi/video_extension.rst
@@ -1,5 +1,8 @@
+.. 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 +11,12 @@ 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 exports the backlight control via a sysfs interface,
+notifies userspace with events and changes the backlight level via ACPI
+firmware, as detailed at the following chapters:

-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
@@ -22,36 +28,41 @@ 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
+
+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:
+the following _BCL package::

-Method (_BCL, 0, NotSerialized)
-{
- Return (Package (0x0C)
+ Method (_BCL, 0, NotSerialized)
{
- 0x64,
- 0x32,
- 0x0A,
- 0x14,
- 0x1E,
- 0x28,
- 0x32,
- 0x3C,
- 0x46,
- 0x50,
- 0x5A,
- 0x64
- })
-}
+ 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
@@ -62,13 +73,15 @@ 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 +97,27 @@ 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.
--
2.20.1