From: Mario Limonciello Date: Tue, 15 Apr 2025 19:20:59 +0000 (-0500) Subject: docs: backlight: Clarify `actual_brightness` X-Git-Tag: v6.16-rc1~33^2~20^2~12 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=8ecd32b668238a7a79b2f44b66dae8ffb87ac763;p=linux-block.git 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 Cc: Lennart Poettering Cc: richard.purdie@linuxfoundation.org Link: https://github.com/systemd/systemd/pull/36881 Reviewed-by: Harry Wentland Link: https://lore.kernel.org/r/20250415192101.2033518-1-superm1@kernel.org Signed-off-by: Mario Limonciello --- 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 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//max_brightness