Directed power management
Directed Deepest Runtime Idle Platform State (DDRIPS) refers to mechanisms by which the OS directs devices to enter their appropriate low-power idle states when the system goes idle, thereby enabling the system to enter low power more reliably.
DDRIPS applies only to Modern Standby systems and targets only those devices that are constraints for DRIPS and their child devices, if any. Child devices can be devices that are directly enumerated by the parent device or that have a power relation with the parent device.
DDRIPS comprises two mechanisms, Directed PoFx (DFx) and Device-S4. For device stacks that support both mechanisms, both mechanisms can be used to power down different devices in the device tree depending on which mechanisms each individual device supports.
DFx is an extension to PoFx that enables the power manager to direct a device to enter a lower power state. DFx takes effect after a DRIPS constraint device has been active for at least two consecutive minutes (driver-configurable timeout, default 2 minutes) when the system is in Modern Standby and there is no activator-brokered software activity running. DFx directs devices to enter their target D-state for Modern Standby with the ability to arm for wake as they may during a normal Modern Standby transition. It does not carry the assumptions associated with an S-IRP, e.g. device reset is not required. DFx will not power down paging or debug devices.
DFx is enabled on both AC and DC power.
Device-S4 provides a means to leverage existing S-IRP logic in drivers to initiate a D-state transition. Device-S4 takes effect after a DRIPS constraint device has been active for at least five consecutive minutes when the system is in Modern Standby and there is no activator-brokered software activity running. Device stacks must advertise a means to be reset or power cycled to be included in the Device-S4 transition.
Just like a normal S4 transition, Device-S4 a global operation where all applications and services are suspended and system functionality is akin to S3/S4. However, the S4-IRP is sent only to the offending device or device subtree in the device hierarchy. From the perspective of the device receiving a Device-S4, it is indistinguishable from a normal S4 transition. The device will enter the same D-state as during an S4 transition.
Device-S4 is enabled by default for USB devices, and it can be enabled via opt-in for PCIe plug-in devices on desktops. Keyboards and mice are excluded from Device-S4 in order to preserve their ability to wake from Modern Standby.
On desktop form factor systems, Device-S4 is enabled on AC power. On mobile form factor systems, Device-S4 is enabled only on DC power.