Sounds stupid, but I'm really impressed now! But... is there a reason C4 is not enabled by default then? I mean, if it makes trouble, you can always disable it (at least on Linux) with the command line parameters as discussed previously. Imho, it should be at least configurable using the regular config mechanism.
I guess, just nobody tried it before on a ThinkPad. The entries for C1/C2 are most probably copy-pasted from Roda/RK9. Thanks for testing this through! If you don't want to go further (https://coreboot.org/Git) somebody else will likely write a patch ;)
Okay, but that's strange, because e.g. my X60 supports C4 although it also seems to consume way too much power. Will have to investigate that as well. I also have this other X200 with P8600 and CCFL backlight, but one can assume that the patch will work there as well. But if I find the time I can test it there as well if nobody else wants to do that. I assume once it gets in git, we will automatically get more testers anyways. ;-)
And yes, I can submit the patch but not today, it's already 1:40am over here.
Cheers, Daniel