This parameter allows the user to set the link (interface) power management.
There are 3 possible options:
Tell the controller to try to make the link use the
least possible power when possible. This may
sacrifice some performance due to increased latency
when coming out of lower power states.
Generally, this means no power management. Tell
the controller to have performance be a priority
over power management.
Tell the controller to enter a lower power state
when possible, but do not enter the lowest power
state, thus improving latency over min_power setting.