amd64/181357: LCD Brightness Control not working on Lenovo X121e (ACPI issue?)

[Matthias Petermann]

Hello,

regarding this PR I made some further observation. Even the 
acpi_ec_write seems to not have any effect on the brightness, the values 
set to the appropriate register (IBM_EC_BRIGHTNESS   0x31) survive a 
reboot.

Looks like the values are stored correctly, but EC doesn't care for them 
when setting brightness?

I'm not sure where to look next. Could this be a hardware issue with the 
Device?

Kind regards,
Matthias