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Diffstat (limited to 'Documentation/acpi/video_extension.txt')
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diff --git a/Documentation/acpi/video_extension.txt b/Documentation/acpi/video_extension.txt deleted file mode 100644 index 79bf6a4921be..000000000000 --- a/Documentation/acpi/video_extension.txt +++ /dev/null @@ -1,106 +0,0 @@ -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: - -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. |