Device power management reference
Drivers can divide their device hardware into multiple logical components to enable fine-grained power management. A component has a set of power states that can be managed independently of the power states of other components in the same device. In the F0 state, the component is fully turned on. The component might support additional, low-power states F1, F2, and so on.
The power policy owner for a device is typically the device's function driver. To enable component-level power management, this driver registers the device with the power management framework (PoFx). By registering the device, the driver assumes the responsibility for informing PoFx when a component is actively being used and when the component is idle. PoFx makes intelligent idle state choices for the device based on information about the component activity, latency tolerance, expected idle durations, and wake requirements. By controlling power usage at the component level, PoFx can reduce power requirements while preserving system responsiveness. For more information, see Component-Level Power Management.
Device Power Management Routines
These routines are implemented by the power management framework (PoFx) to enable device power management. These routines are called by the driver that is the power policy owner (PPO) for a device. Typically, the function driver for a device is the PPO for this device.
| Topic | Description |
|---|---|
| PoFxActivateComponent | The PoFxActivateComponent routine increments the activation reference count on the specified component. |
| PoFxCompleteDevicePowerNotRequired | The PoFxCompleteDevicePowerNotRequired routine notifies the power management framework (PoFx) that the calling driver has completed its response to a call to the driver's DevicePowerNotRequiredCallback callback routine. |
| PoFxCompleteIdleCondition | The PoFxCompleteIdleCondition routine informs the power management framework (PoFx) that the specified component has completed a pending change to the idle condition. |
| PoFxCompleteIdleState | The PoFxCompleteIdleState routine informs the power management framework (PoFx) that the specified component has completed a pending change to an Fx state. |
| PoFxIdleComponent | The PoFxIdleComponent routine decrements the activation reference count on the specified component. |
| PoFxIssueComponentPerfStateChange | The PoFxIssueComponentPerfStateChange routine submits a request to place a device component in a particular performance state. |
| PoFxIssueComponentPerfStateChangeMultiple | The PoFxIssueComponentPerfStateChangeMultiple routine submits a request to change the performance states in multiple performance state sets simultaneously for a device component. |
| PoFxNotifySurprisePowerOn | The PoFxNotifySurprisePowerOn routine notifies the power management framework (PoFx) that a device was turned on as a side effect of supplying power to some other device. |
| PoFxPowerControl | The PoFxPowerControl routine sends a power control request to the power management framework (PoFx). |
| PoFxQueryCurrentComponentPerfState | The PoFxQueryCurrentComponentPerfState routine retrieves the active performance state in a component's performance state set. |
| PoFxRegisterComponentPerfStates | The PoFxRegisterComponentPerfStates routine registers a device component for performance state management by the power management framework (PoFx). |
| PoFxRegisterDevice | The PoFxRegisterDevice routine registers a device with the power management framework (PoFx). |
| PoFxReportDevicePoweredOn | The PoFxReportDevicePoweredOn routine notifies the power management framework (PoFx) that the device completed the requested transition to the D0 (fully on) power state. |
| PoFxSetComponentLatency | The PoFxSetComponentLatency routine specifies the maximum latency that can be tolerated in the transition from the idle condition to the active condition in the specified component. |
| PoFxSetComponentResidency | The PoFxSetComponentResidency routine sets the estimated time for how long a component is likely to remain idle after the component enters the idle condition. |
| PoFxSetComponentWake | The PoFxSetComponentWake routine indicates whether the driver arms the specified component to wake whenever the component enters the idle condition. |
| PoFxSetDeviceIdleTimeout | The PoFxSetDeviceIdleTimeout routine specifies the minimum time interval from when the last component of the device enters the idle condition to when the power management framework (PoFx) calls the driver's DevicePowerNotRequiredCallback callback routine. |
| PoFxStartDevicePowerManagement | The PoFxStartDevicePowerManagement routine completes the registration of a device with the power management framework (PoFx) and starts device power management. |
| PoFxUnregisterDevice | The PoFxUnregisterDevice routine removes the registration of a device from the power management framework (PoFx). |
Device Power Management Callbacks
These callback routines are required by the power management framework (PoFx) to enable device power management. The driver that is the power policy owner for the device implements these callback routines. PoFx calls these routines to query and configure the power states of the components in the device.
| Topic | Description |
|---|---|
| ComponentActiveConditionCallback | The ComponentActiveConditionCallback callback routine notifies the driver that the specified component completed a transition from the idle condition to the active condition. |
| ComponentIdleConditionCallback | The ComponentIdleConditionCallback callback routine notifies the driver that the specified component completed a transition from the active condition to the idle condition. |
| ComponentIdleStateCallback | The ComponentIdleStateCallback callback routine notifies the driver of a pending change to the Fx power state of the specified component. |
| ComponentPerfStateCallback | The ComponentPerfStateCallback callback routine notifies the driver that its request to change the performance state of a component is complete. |
| DevicePowerNotRequiredCallback | The DevicePowerNotRequiredCallback callback routine notifies the device driver that the device is not required to stay in the D0 power state. |
| DevicePowerRequiredCallback | The DevicePowerRequiredCallback callback routine notifies the device driver that the device must enter and remain in the D0 power state. |
| PowerControlCallback | The PowerControlCallback callback routine performs a power control operation that is requested by the power management framework (PoFx). |
Device Power Management Structures
The power management framework (PoFx) defines these structures to support device power management.
| Topic | Description |
|---|---|
| PO_FX_COMPONENT_V1 PO_FX_COMPONENT_V2 | The PO_FX_COMPONENT structure describes the power state attributes of a component in a device. |
| PO_FX_COMPONENT_IDLE_STATE | The PO_FX_COMPONENT_IDLE_STATE structure specifies the attributes of an Fx power state of a component in a device. |
| PO_FX_COMPONENT_PERF_INFO | The PO_FX_COMPONENT_PERF_INFO structure describes all the sets of performance states for a single component within a device. |
| PO_FX_COMPONENT_PERF_SET | The PO_FX_COMPONENT_PERF_SET structure represents a set of performance states for a single component within a device. |
| PO_FX_DEVICE_V1 PO_FX_DEVICE_V2 PO_FX_DEVICE_V3 | The PO_FX_DEVICE structure describes the power attributes of a device to the power management framework (PoFx). |
| PO_FX_PERF_STATE | The PO_FX_PERF_STATE structure represents a performance state for a single component within a device. |
| PO_FX_PERF_STATE_CHANGE | The PO_FX_PERF_STATE_CHANGE structure contains information about a change to a performance state that is being requested by calling the PoFxIssueComponentPerfStateChange or PoFxIssueComponentPerfStateChangeMultiple routine. |
Device Power Management Enumerations
The power management framework (PoFx) defines these enumerations to support device power management.
| Topic | Description |
|---|---|
| PO_FX_PERF_STATE_TYPE | The PO_FX_PERF_STATE_TYPE enumeration contains values that describe the type of performance states in a PO_FX_COMPONENT_PERF_SET. |
| PO_FX_PERF_STATE_UNIT | The PO_FX_PERF_STATE_UNIT enumeration contains values that describe the type of unit that is controlled by the performance states in a PO_FX_COMPONENT_PERF_SET. |
Device Power Management Constants
PO_FX_FLAG_XXX flag bits
The PO_FX_FLAG_XXX constants are flag bits that indicate whether a request to change the condition of component is performed synchronously or asynchronously.
#define PO_FX_FLAG_BLOCKING 0x1
#define PO_FX_FLAG_ASYNC_ONLY 0x2
PO_FX_FLAG_XXX constants
| Constant | Description |
|---|---|
| PO_FX_FLAG_BLOCKING | Make the condition change synchronous. If this flag is set, the routine that requests the condition change does not return control to the calling driver until the component hardware completes the transition to the new condition. This flag can be used only if the caller is running at IRQL < DISPATCH_LEVEL. |
| PO_FX_FLAG_ASYNC_ONLY | Make the condition change fully asynchronous. If this flag is set, the calling driver's callback routine is called from a thread other than the thread in which the routine that requests the condition change is called. Thus, the routine that requests the condition change always returns asynchronously without waiting for the callback to complete. |
PO_FX_FLAG_XXX remarks
The Flags parameter to the following routines can be set to a PO_FX_FLAG_XXX constant:
- PoFxActivateComponent
- PoFxIdleComponent
- PoFxIssueComponentPerfStateChange
- PoFxIssueComponentPerfStateChangeMultiple
The PO_FX_FLAG_BLOCKING and PO_FX_FLAG_ASYNC_ONLY flag bits are mutually exclusive. The caller can set one or the other flag bit in the Flags parameter, but not both flag bits.
PO_FX_FLAG_XXX Requirements
| Version | Header |
|---|---|
| Supported starting with Windows 8. | Wdm.h |
PO_FX_FLAG_PERF_XXX flag bits
The PO_FX_FLAG_PERF_XXX constants are flag bits that define how the power management framework (PoFx) manages performance states for a device component.
#define PO_FX_FLAG_PERF_PEP_OPTIONAL 0x1
#define PO_FX_FLAG_PERF_QUERY_ON_F0 0x2
#define PO_FX_FLAG_PERF_QUERY_ON_ALL_IDLE_STATES 0x4
| Constant | Value | Description |
|---|---|---|
| PO_FX_FLAG_PERF_PEP_OPTIONAL | 1 (0x1) | Indicates that the driver can change performance states without assistance from the platform extension plug-in (PEP), or that the driver is registering performance states with PoFx for logging purposes only. If this flag is set, the PoFxRegisterComponentPerfStates call will still succeeded if the PEP does not support performance states for the component. |
| PO_FX_FLAG_PERF_QUERY_ON_F0 | 2 (0x2) | For some devices, the PEP may need to a place a performance state set for a component into a certain performance state (known as a nominal performance state) when it idles the component. Drivers set this flag if the component contains nominal performance states, in which case PoFx will query the PEP to determine the current performance state when the component transitions to F0. |
| PO_FX_FLAG_PERF_QUERY_ON_ALL_IDLE_STATES | 4 (0x4) | For some devices, the PEP may need to a place a performance state set for a component into a certain performance state (known as a nominal performance state) when it transitions the component between idle states. Drivers set this flag if this component contains nominal performance states, in which case PoFx will query the PEP to determine the current performance state when the component transitions between idle states. |
PO_FX_FLAG_PERF_XXX remarks
The Flags parameter to the PoFxRegisterComponentPerfStates routine can be set to a PO_FX_FLAG_PERF_XXX constant.
PO_FX_FLAG_PERF_XXX requirements
| Requirements | Version |
|---|---|
| Supported starting with Windows 10. | Wdm.h |