Handling a System Set-Power IRP in a Device Power Policy Owner
In response to a system set-power IRP, the power policy owner for a device stack is responsible for putting its device stack into an appropriate device power state.
As a general rule, when a device power policy owner receives an IRP_MN_SET_POWER for a system power state, it should respond by passing the system set-power IRP down the device stack. A device power policy owner should also respond by sending down the device stack IRP_MN_SET_POWER for a corresponding device power state in an IoCompletion routine. After all drivers in the stack have completed the device set-power IRP, the device power policy owner completes the system set-power IRP.
However, to improve system resume performance, device power owners for devices that do not have child devices should use a different approach to reduce the time it takes a system to return to working state S0 from a sleeping state. In this case, in response to a system set-power IRP that returns a system to working state S0, device power policy owners should perform the following sequence of operations:
After receiving an IRP_MN_SET_POWER IRP for the S0 system power state in the driver's DispatchPower routine, set an IoCompletion routine for the IRP and pass the IRP down the stack.
In the IoCompletion routine set in step (1), request an IRP_MN_SET_POWER IRP for the corresponding device power state and then immediately complete the system set-power IRP. The driver should not wait for device set-power IRPs to complete before it completes the system set-power IRP. The IoCompletion routine is executed after all lower-level drivers have completed the system set-power IRP and the system set-power IRP is passed back to the driver's functional device object (FDO).
Perform any required device-specific initialization.
Complete the device set-power IRP that was sent in step (2).
Process I/O requests that were queued when the device was in a device sleeping state.
The kernel power manager has a limited set of IRP dispatch queues, and must quickly notify all devices in the system of the return to the system working state S0. Drivers that fail to complete the system set-power IRP as quickly as possible prevent other devices from getting their system set-power IRP, which can adversely affect overall system performance during system power-state transitions.
For more detail on handling system set-power IRPs, see the following: