On Wed, 6 Oct 2010, Rafael J. Wysocki wrote:

quoted

Mobile folks wish to power down some devices (most often input -
touchscreen, keypad) under certain circumstances to save power.
So far they were doing that by adding "disable" hook to individual
drivers and while I did allow that in for some devices I feel that we
need more standardised solution, preferably one that could re-use
existing PM hooks in drivers.

There's no interface for that at the PM core level, but I think we should
add it, perhaps in analogy to the autosuspend one.  Namely, we can add a
flag for drivers who want to make their suspend/resume callbacks to be
reachable directly from user space.  Setting that flag would enable a sysfs
attribute in /sys/devices/.../power/ allowing user space to invoke
pm_runtime_suspend() and pm_runtime_resume() for the given device.

We already have power/control.  If the subsystem sets it to "on" by 
default and the driver suspends the device whenever it is idle, then 
userspace can control the power level by writing "auto" or "on" to 
power/control.

Alan Stern