Writing Device Drivers

Power Levels

The current implementation of the Device Power Management framework only keeps track of two power levels for each device, its current power level and its normal power level. The normal power level of a component is the power level required for normal operation of the component, and is the power level to which the component is returned by the framework when the device is needed. The device driver informs the framework of the normal power level of the component by calling pm_set_normal_power(9F).

The current power level of the component is the power level at which the component is currently operating. The device driver should ensure that the component is set to the normal power level at initialization time. The framework assumes that when a device attaches it will be operating at its normal power level until the framework power manages it.

Power-level values that represent power on states must be positive integers greater than zero. A value of zero means the device has been set to the lowest operating power available.