From: Mario Limonciello <mario.limoncie...@amd.com>
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 <l...@kernel.org>
Cc: Lennart Poettering <lenn...@poettering.net>
Cc: richard.pur...@linuxfoundation.org
Link: https://github.com/systemd/systemd/pull/36881
Signed-off-by: Mario Limonciello <mario.limoncie...@amd.com>
---
v2:
* Add more explanation
---
Documentation/ABI/stable/sysfs-class-backlight | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/Documentation/ABI/stable/sysfs-class-backlight
b/Documentation/ABI/stable/sysfs-class-backlight
index 6102d6bebdf9a..40b8c46b95b28 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 <rpur...@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
--
2.43.0
