This is the core of the USB_SUSPEND functionality.  Please merge.

This adds an experimental CONFIG_USB_SUSPEND option, which supports the
USB "suspend" state.  Linux-USB hosts have previously ignored that state.

    -	New driver API calls, usb_suspend_device() and its
	sibling usb_resume_device().

    -	Access to those calls through sysfs, such as
		echo -n 2 > power/state
		echo -n 0 > power/state

That can be used to reduce the power consumption of any given USB device,
then re-activate it later.  Eventually, most USB device drivers should
probably suspend idle USB devices.

One problem with this patch:  USB drivers without suspend() callbacks
may badly misbehave.  Right now only hub drivers know suspend().  If the
driver core didn't self-deadlock when we try it, unbinding those drivers
from those devices (then re-enumerating on resume) would be perfect...
the current compromise is just to emit a warning message.

In conjunction with host controller driver support (already merged for
OHCI and EHCI), PCI host controllers will issue the PME# wakeup signal
when a USB keyboard starts remote wakeup signaling.  (But the keyboard
wasn't usable later, since HID doesn't try to suspend.)

I understand some ACPI patches are circulating, and maybe already in
the MM tree, to make a suspended system wake up given PME# signaling.
It'd be great if someone made that work transparently with USB, but
for now I'm told it'll need some sysfs setup first.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>