Dependency

A device might depend on one or more other devices. A device depends on another device if it can be powered off only when all the components of all the devices it depends on are also powered off. For example, when the window system is not running, the frame buffer device depends on the keyboard device by default. When the window system is not running, the frame buffer components can only be powered off when the keyboard device is powered off.

The power.conf(4) file specifies the dependencies among devices. A parent node in the device tree implicitly depends upon its children. This dependency is handled automatically by the power management framework.