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| author |   Mario Limonciello <mario.limonciello@amd.com> | 2025-04-15 14:20:59 -0500 |
|---|---|---|
| committer | Mario Limonciello <mario.limonciello@amd.com> | 2025-05-05 13:43:00 -0500 |
| commit | 8ecd32b668238a7a79b2f44b66dae8ffb87ac763 (patch) | |
| tree | 146da1c7ef8c0de72b2eb3d049b44168f74e8cbe | |
| parent | drm/bridge: anx7625: change the gpiod_set_value API (diff) | |
| download | wireguard-linux-8ecd32b668238a7a79b2f44b66dae8ffb87ac763.tar.xz wireguard-linux-8ecd32b668238a7a79b2f44b66dae8ffb87ac763.zip | |
docs: backlight: Clarify `actual_brightness`
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
6ca017658b1f9 ("[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>
| -rw-r--r-- | Documentation/ABI/stable/sysfs-class-backlight | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/Documentation/ABI/stable/sysfs-class-backlight b/Documentation/ABI/stable/sysfs-class-backlight index 6102d6bebdf9..40b8c46b95b2 100644 --- a/Documentation/ABI/stable/sysfs-class-backlight +++ b/Documentation/ABI/stable/sysfs-class-backlight @@ -26,7 +26,12 @@ Date: March 2006 KernelVersion: 2.6.17 Contact: Richard Purdie <rpurdie@rpsys.net> Description: - Show the actual brightness by querying the hardware. + 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 |