PO_FX_DEVICE_POWER_REQUIRED_CALLBACK callback function (wdm.h)

Article
02/28/2023

The DevicePowerRequiredCallback callback routine notifies the device driver that the device must enter and remain in the D0 power state.

Syntax

PO_FX_DEVICE_POWER_REQUIRED_CALLBACK PoFxDevicePowerRequiredCallback;

void PoFxDevicePowerRequiredCallback(
  [in] PVOID Context
)
{...}

Parameters

[in] Context

A pointer to the device context. The device driver uses this context to store information about the current power state of the device. The device driver specified this pointer in the DeviceContext member of the PO_FX_DEVICE structure that the driver used to register the device with the power management framework (PoFx). This context is opaque to PoFx.

Return value

None

Remarks

After PoFx calls the driver's DevicePowerRequiredCallback routine, the driver must initiate a transition to the D0 state by sending a D0 IRP (an IRP_MN_SET_POWER request) down the device stack, if the device is not already in the D0 state. After the driver completes (and all lower drivers complete) handling of this request, the driver must call the PoFxReportDevicePoweredOn routine. The PoFxReportDevicePoweredOn call notifies PoFx that the device completed its response to the DevicePowerRequiredCallback call. The driver can call PoFxReportDevicePoweredOn during or after the DevicePowerRequiredCallback call.

Each time the DevicePowerRequiredCallback routine is called, the driver must respond by calling PoFxReportDevicePoweredOn. The PoFxReportDevicePoweredOn call can occur either during or after the DevicePowerRequiredCallback call. The driver must call PoFxReportDevicePoweredOn regardless of whether no D0 IRP is required, the D0 IRP request fails, or the dispatched D0 IRP succeeds or fails.

PoFx calls the DevicePowerRequiredCallback routine only if PoFx previously called the driver's DevicePowerNotRequiredCallback routine to notify the driver that the device was not required to stay in the D0 state.

The call to the DevicePowerRequiredCallback routine can occur at any time after the driver calls PoFxCompleteDevicePowerNotRequired to complete a DevicePowerNotRequiredCallback callback. The DevicePowerRequiredCallback call does not necessarily occur as a result of an action taken by the driver, such as requesting that a component change to the active condition.

Examples

To define a DevicePowerRequiredCallback callback routine, you must first provide a function declaration that identifies the type of callback routine you're defining. Windows provides a set of callback function types for drivers. Declaring a function using the callback function types helps Code Analysis for Drivers, Static Driver Verifier (SDV), and other verification tools find errors, and it's a requirement for writing drivers for the Windows operating system.

For example, to define a DevicePowerRequiredCallback callback routine that is named MyDevicePowerRequiredCallback, use the PO_FX_DEVICE_POWER_REQUIRED_CALLBACK type as shown in this code example:

PO_FX_DEVICE_POWER_REQUIRED_CALLBACK MyDevicePowerRequiredCallback;

Then, implement your callback routine as follows:

_Use_decl_annotations_
VOID
  MyDevicePowerRequiredCallback(
    PVOID Context
    )
  {
      // Function body
  }

The PO_FX_DEVICE_POWER_REQUIRED_CALLBACK function type is defined in the Wdm.h header file. To more accurately identify errors when you run the code analysis tools, be sure to add the _Use_decl_annotations_ annotation to your function definition. The _Use_decl_annotations_ annotation ensures that the annotations that are applied to the PO_FX_DEVICE_POWER_REQUIRED_CALLBACK function type in the header file are used. For more information about the requirements for function declarations, see Declaring Functions by Using Function Role Types for WDM Drivers. For information about _Use_decl_annotations_, see Annotating Function Behavior.

Requirements

Requirement	Value
Minimum supported client	Supported starting with Windows 8.
Target Platform	Desktop
Header	wdm.h (include Wudfwdm.h)
IRQL	Called at IRQL <= DISPATCH_LEVEL.

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