I have a Thinkpad X1 Carbon (4th gen). I'm running debian sid with 4.5 kernel. It seems that I couldn't get past PC2. I've updated my kernel to the latest in experimental which is 4.6 and I'm reaching PC8.
I'm not sure if the BIOS/firwmare/microcode upgrade made any real difference or if it was just the kernel because it did reach PC8 with just the kernel upgrade.
Hopefully this will improve the battery life a bit.
4.6 seems to have better support
C2 (pc2) 12.2%
C3 (pc3) 0.2%
C6 (pc6) 39.4%
C7 (pc7) 0.0%
C8 (pc8) 14.1%
C9 (pc9) 0.0%
C10 (pc10) 0.0%
I've also flashed the BIOS to the latest version:
BIOS Revision: 1.14 Firmware Revision: 1.9
microcode revision=0x88.
I'm not sure if the BIOS/firwmare/microcode upgrade made any real difference or if it was just the kernel because it did reach PC8 with just the kernel upgrade.
Hopefully this will improve the battery life a bit.