Well if you are simply talking about the sysfs stuff under /sys/devices/system/cpu/cpu0/cpuidle/ then I have to tell you that my kernel does c3 on cpu0 out of the boxRetention state was added a while back. You need to look back much further. CAF officially enabled retention recently.
The deeper states aren't enabled but with my app (or via sysfs you can enable them as well). This should help screen on battery a bit. When core 0 is idling, now it can go into deeper state. Core 1~3 are unplugged so won't affect them at all.
On my sensation kernel, I completely disabled hot plugging altogether, at the same time I enabled deeper sleep states while idling resulting in better battery life than stock performance with mpdecision.
Too bad the current krait processors have he bugs, the effects are not as great as the older 8x60 s3 generation. (The newer kraits like HTC one and sgs 4, may have the bug fixed)
Code:
[email protected]:/sys # cat devices/system/cpu/cpu0/cpuidle/state3/name
C3
# cat devices/system/cpu/cpu0/cpuidle/state3/usage
243301