So.. after upgrading my laptop's UEFI to the latest version, my laptops kb's backlight doesn't work properly anymore. Wonderful.
It appears that an invalid value is now 'stuck' in the NCB ( 0xff ) and the boot-up backlight level is stuck due to a bug in the DSDT in the SLKB and EC0 WAK methods.
( 0xff ) AND 0x7f
KBLV = 0x7f
0x7f is an invalid index for the PWKB buffer.
The 0xff value passes the significant value 'AND test' so it is then stored in Local0 which is then stored in WRAM 0x044b.
Compounding the problem is that the EC0's 'WAK' method ignores invalid values that were stored without removing them from the non-volatile memory area. Instead it puts 0's in the volatile memory area (0x044b). Could explain why the kblight 'forgets' the last brightness value on powercycle or wake and gets stuck off.
Looks like the 'TSTP' (?) should be preserving the last level of brightness in the non-volatile area between state changes. With the BIOS update 209 it appears to not be functioning as intended.
It'd be great if this was fixed -- even if the fix was to a force a set brightness level at all states.
