Writing values to the register breaks backlight control - i.e., using the Function keys to invoke XF86MonBrightnessUp and XF86MonBrightnessDown (see xev, Function Keys)
Writing to the appropriate /sys/class file still works:
echo '13' | sudo tee /sys/class/backlight/acpi_video0/brightness
Issue fixed by disabling boot and sleep services.
Using a ThinkPad T400 on 20210522.
[Offending documentation](https://libreboot.org/docs/misc/#finetune-backlight-control-on-intel-gpus)
Writing values to the register breaks backlight control - i.e., using the Function keys to invoke `XF86MonBrightnessUp` and `XF86MonBrightnessDown` (see `xev`, [Function Keys](https://wiki.archlinux.org/title/Lenovo_ThinkPad_T400#Function_keys))
Writing to the appropriate `/sys/class` file still works:
`echo '13' | sudo tee /sys/class/backlight/acpi_video0/brightness`
Issue fixed by disabling boot and sleep services.
Using a ThinkPad T400 on 20210522.
Implicitly, it appears [pulse width modulation detection was fixed upstream](https://teddit.net/r/libreboot/comments/7dt2l5/x200_ccfl_permanent_backlight_fix/dqlp9gp/#c).
Offending documentation
Writing values to the register breaks backlight control - i.e., using the Function keys to invoke
XF86MonBrightnessUp
andXF86MonBrightnessDown
(seexev
, Function Keys)Writing to the appropriate
/sys/class
file still works:echo '13' | sudo tee /sys/class/backlight/acpi_video0/brightness
Issue fixed by disabling boot and sleep services.
Using a ThinkPad T400 on 20210522.
Implicitly, it appears pulse width modulation detection was fixed upstream.
Can you fix the documentation yourself? Then you can submit a pull request
Done in #2
can you please re-submit the fix to the docs