Comment # 13 on bug 967490 from Thomas Mitterfellner

Unfortunately, it will take a little while until I can test this on the machine
itself, BUT: I'm pretty sure /sys/bus/usb/devices/$DEVICE/power/level does not
exist as you can see from the output of

for i in /sys/bus/usb/devices/1-6:1.0/power/* ; do echo -n "$i: " ; cat $i ;
done

I posted above, i.e. the only files residing there are:

async, runtime_active_kids, runtime_enabled, runtime_status, and runtime_usage.

That said, I could of course try the two echo commands. OTOH, I just read here
https://www.kernel.org/doc/Documentation/usb/power-management.txt that
power/level is deprecated since kernel 2.6.35, so I should probably try this
with power/control?