On Lenovo Yoga 900 with 4.6.0 rc3, the C-states (beyond C2) seem not to get enabled. Still considerable battery lifetime.

➜ ~ powertop

Package
C2 (pc2) 53.0% |
C3 (pc3) 0.0% |
C6 (pc6) 0.0% |
C7 (pc7) 0.0% |
C8 (pc8) 0.0% |
C9 (pc9) 0.0% |
C10 (pc10) 0.0% |

➜ ~ grep . /sys/devices/system/cpu/cpuidle/*
/sys/devices/system/cpu/cpuidle/current_driver:intel_idle
/sys/devices/system/cpu/cpuidle/current_governor_ro:menu

➜ ~ sudo rdmsr 0xE2
1e008006

➜ ~ dmesg | grep -i error
[ 2.894522] EXT4-fs (sda9): re-mounted. Opts: errors=remount-ro
[ 2.958327] tpm_crb: probe of MSFT0101:00 failed with error -16
[ 3.069000] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-8000C-21.ucode failed with error -2
[ 3.069357] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-8000C-20.ucode failed with error -2
[ 3.069371] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-8000C-19.ucode failed with error -2
[ 3.069380] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-8000C-18.ucode failed with error -2
[ 3.069390] iwlwifi 0000:01:00.0: Direct firmware load for iwlwifi-8000C-17.ucode failed with error -2
[ 3.404045] i2c_hid i2c-ITE8396:00: error in i2c_hid_init_report size:19 / ret_size:18