Ezekeel/Nexus-S-reference-kernel — comment on commit 945d2b961a237a205ef4966f70f95644f1ff7042
File: drivers/misc/deep_idle.c line 17
By stevegaron:

With the value at False, deep idle is Disabled at boot.
With the value to True, deep idle is Enabled at boot.

In both cases, you can use the sys interface to turn it on/off without rebooting.