With power management, if the host bus adapter only needs to power down when all target adapters are at power level 0, the HBA driver only needs to provide a power(9E) entry point. Refer to Chapter 12, Power Management. The HBA driver also needs to create a pm-components(9P) property that describes the components that the device implements.
Nothing more is necessary, since the components will default to idle, and the power management framework's default dependency processing will ensure that the host bus adapter will be powered up whenever an target adapter is powered up. Provided that automatic power management is enabled automatically, the processing will also power down the host bus adapter when all target adapters are powered down ().