mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-08-05 16:54:27 +00:00
8ecd32b668
Currently userspace software systemd treats `brightness` and
`actual_brightness` identically due to a bug found in an out of tree
driver.
This however causes problems for in-tree drivers that use brightness
to report user requested `brightness` and `actual_brightness` to report
what the hardware actually has programmed.
Clarify the documentation to match the behavior described in commit
6ca017658b ("[PATCH] backlight: Backlight Class Improvements").
Cc: Lee Jones <lee@kernel.org>
Cc: Lennart Poettering <lennart@poettering.net>
Cc: richard.purdie@linuxfoundation.org
Link: https://github.com/systemd/systemd/pull/36881
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Link: https://lore.kernel.org/r/20250415192101.2033518-1-superm1@kernel.org
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
63 lines
2.2 KiB
Text
63 lines
2.2 KiB
Text
What: /sys/class/backlight/<backlight>/bl_power
|
|
Date: April 2005
|
|
KernelVersion: 2.6.12
|
|
Contact: Richard Purdie <rpurdie@rpsys.net>
|
|
Description:
|
|
Control BACKLIGHT power, values are compatible with
|
|
FB_BLANK_* from fb.h
|
|
|
|
- 0 (FB_BLANK_UNBLANK) : power on.
|
|
- 4 (FB_BLANK_POWERDOWN) : power off
|
|
Users: HAL
|
|
|
|
What: /sys/class/backlight/<backlight>/brightness
|
|
Date: April 2005
|
|
KernelVersion: 2.6.12
|
|
Contact: Richard Purdie <rpurdie@rpsys.net>
|
|
Description:
|
|
Control the brightness for this <backlight>. Values
|
|
are between 0 and max_brightness. This file will also
|
|
show the brightness level stored in the driver, which
|
|
may not be the actual brightness (see actual_brightness).
|
|
Users: HAL
|
|
|
|
What: /sys/class/backlight/<backlight>/actual_brightness
|
|
Date: March 2006
|
|
KernelVersion: 2.6.17
|
|
Contact: Richard Purdie <rpurdie@rpsys.net>
|
|
Description:
|
|
Show the actual brightness by querying the hardware. Due
|
|
to implementation differences in hardware this may not
|
|
match the value in 'brightness'. For example some hardware
|
|
may treat blanking differently or have custom power saving
|
|
features. Userspace should generally use the values in
|
|
'brightness' to make decisions.
|
|
Users: HAL
|
|
|
|
What: /sys/class/backlight/<backlight>/max_brightness
|
|
Date: April 2005
|
|
KernelVersion: 2.6.12
|
|
Contact: Richard Purdie <rpurdie@rpsys.net>
|
|
Description:
|
|
Maximum brightness for <backlight>.
|
|
Users: HAL
|
|
|
|
What: /sys/class/backlight/<backlight>/type
|
|
Date: September 2010
|
|
KernelVersion: 2.6.37
|
|
Contact: Matthew Garrett <mjg@redhat.com>
|
|
Description:
|
|
The type of interface controlled by <backlight>.
|
|
"firmware": The driver uses a standard firmware interface
|
|
"platform": The driver uses a platform-specific interface
|
|
"raw": The driver controls hardware registers directly
|
|
|
|
In the general case, when multiple backlight
|
|
interfaces are available for a single device, firmware
|
|
control should be preferred to platform control should
|
|
be preferred to raw control. Using a firmware
|
|
interface reduces the probability of confusion with
|
|
the hardware and the OS independently updating the
|
|
backlight state. Platform interfaces are mostly a
|
|
holdover from pre-standardisation of firmware
|
|
interfaces.
|