PO_FX_COMPONENT_V1 structure (wdm.h)

Article
02/25/2022

The PO_FX_COMPONENT structure describes the power state attributes of a component in a device.

Syntax

typedef struct _PO_FX_COMPONENT_V1 {
  GUID                        Id;
  ULONG                       IdleStateCount;
  ULONG                       DeepestWakeableIdleState;
  PPO_FX_COMPONENT_IDLE_STATE IdleStates;
} PO_FX_COMPONENT_V1, *PPO_FX_COMPONENT_V1;

Members

Id

A component ID that uniquely identifies this component with respect to the other components in the device. The driver should specify a nonzero value for this member if the power management framework (PoFx) requires a component ID to distinguish this component from other, similar components in the same device. This member is optional. If this member is not used, it must be set to all zeros.

IdleStateCount

The number of elements in the array that is pointed to by the IdleStates member. Additionally, this member specifies the number of Fx power states that the component supports. A component must support at least one Fx state (F0).

DeepestWakeableIdleState

The index of the deepest Fx state from which the component can wake. Specify 0 for F0, 1 for F1, and so on. This index must be less than IdleStateCount.

IdleStates

A pointer to a PO_FX_COMPONENT_IDLE_STATE array. The length of this array is specified by the IdleStateCount member. Each array element specifies the attributes of an Fx power state that is supported by the component. Element 0 describes F0, element 1 describes F1, and so on.

Remarks

When a device driver registers a device with PoFx, the driver supplies a PO_FX_DEVICE structure that holds the registration information. This structure contains an array of PO_FX_COMPONENT structures. The elements in this array describe the power attributes of the individual components in the device. PoFx uses the information in this array to manage the power settings of these components.

The Id member contains a component ID that PoFx can use to uniquely identify a component. Do not confuse the component ID with the component index, which a routine such as PoFxActivateComponent uses to identify a component in a registered device. A component index is an index into the Components array in the PO_FX_DEVICE structure that the device driver used to register the device with PoFx. If the Components array contains N elements, component indexes are integer values in the range 0 to N–1. In contrast, a component ID is a GUID value.

The Flags member may be set to the PO_FX_COMPONENT_FLAG_F0_ON_DX value if the driver specified support for PO_FX_VERSION_V2 during registration with PoFx (that is, during the call to the PoFxRegisterDevice routine, the driver specified the value PO_FX_VERSION_V2 for the Version member of the PO_FX_DEVICE structure that was passed to the Device parameter). If the PO_FX_COMPONENT_FLAG_F0_ON_DX flag is specified, PoFx will place the component into the F0 power state during Dx transitions and for wait/wake IRPs. Before dispatching a Dx IRP or wait/wake IRP to the device stack (whichever event happens first), the power manager will transition the component into the F0 state. The component will be kept in F0 until the wake/wait IRP is canceled or completed, or the Dx IRP is completed and driver has called the PoFxReportDevicePoweredOn routine (whichever event happens last).

Component dependencies

PoFx supports logical component dependencies within a device (but not across different devices). During device registration for each component, the driver can supply a number (the ProviderCount member) and an array of component indexes (the Providers member) this component depends on; these are known as providers. PoFx guarantees that the component will not become active until all of its providers are active.

Component dependencies form a directed graph where an edge points from a dependent component to a provider and represents a dependency. During device registration, PoFx validates the dependency graph: cycles and repeated edges are not allowed and the depth of the graph for the depth-first search traversal cannot exceed four. PoFx also sets the components’ active reference count according to the dependency graph; that is, each provider’s active reference count is incremented once for each component that depends on it.

During the component activation, PoFx asynchronously activates all providers first. After a component is active, PoFx checks every dependent component and continues their activation if necessary.

When the component transitions to the idle state, PoFx first makes the dependent components idle. After the driver completes the ComponentIdleConditionCallback and the platform extension plug-in (PEP) is notified that the component is idle, PoFx recursively traverses the dependency graph in breadth-first traversal and asynchronously idles each provider.

Requirements

Requirement	Value
Minimum supported client	Supported starting with Windows 8.
Header	wdm.h (include Wudfwdm.h)