Comment 28 for bug 136549

I did a little research to find the actual cause of the problem.

There's actually two issues here:

1) powertop suggests to add the usbcore.autosuspend=1 kernel parameter, but we're shipping usbcore as a module (solution described here: https://bugs.launchpad.net/ubuntu/+source/powertop/+bug/136549/comments/16)
this is a confirmed issue, and should be fixed

2) to decide whether to make this suggestion, powertop checks two things:
  a) that /sys/bus/usb/devices/*/power/autosuspend >=0
  b) that /sys/bus/usb/devices/*/power/level != “on”
I have found that in my machine the usb root hubs have power level = "auto", but slave devices (usb mouse, usb storage) have power lever = "on". this causes powertop to make this suggestion.
I am not sure whether powertop is right on this one (i.e. whether the power levels should be auto) or whether the current situation is correct, and powertop should change...