Adding power management capabilities to device drivers

Device drivers on their own can implement a distinct power management capability, which is known as runtime power management. Not all devices support runtime power management. However, those that do must export some callbacks for controlling their power state depending on the user or system’s policy decisions. As we have seen earlier, this is device-specific. In this section, we will learn how to extend device driver capabilities with power management support.

Though device drivers provide runtime power management callbacks, they also facilitate and participate in the system sleep state by providing another set of callbacks, where each set participates in a particular system sleep state. Whenever the system needs to enter or resume from a given set, the kernel will walk through each driver that provided callbacks for this state and then invoke them in a precise order. Simply speaking, device power management consists...