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PortCls Private PEP Context Sharing

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Starting with Windows 8, a miniport driver can use IPortClsRuntimePower, a new interface, for private context sharing with the Windows Power Engine Plug-in (PEP).

The audio port class driver (PortCls) has been updated to expose the new interface, IPortClsRuntimePower, on the WaveRT port. In order for a miniport driver to send private power controls to the operating system's PEP, the miniport driver first has to gain access to the IPortClsRuntimePower interface of its associated port. The miniport driver then registers a callback that is invoked at the appropriate time, allowing the miniport driver to send the private power controls.

Accessing IPortClsRuntimePower

The miniport driver gains access to its port's IPortClsRuntimePower via the following sequence of events:

  1. The miniport driver calls PcNewPort and supplies IID_IPortWaveRT as the REFID.

  2. PcNewPort creates a port interface (Pport) of type IPortWaveRT.

  3. The miniport driver then calls QueryInterface in the newly created IPortWaveRT port interface, and specifies IID_IPortClsRuntimePower as the interface GUID.

  4. The IPortWaveRT port interface provides the miniport driver with a pointer to its IPortClsRuntimePower interface.

The Portcls.h header file defines the GUID for the IPortClsRuntimePower as follows:

// {E057C351-0430-4DBC-B172-C711D40A2373}
DEFINE_GUID(IID_IPortClsRuntimePower,
0xe057c351, 0x430, 0x4dbc, 0xb1, 0x72, 0xc7, 0x11, 0xd4, 0xa, 0x23, 0x73);

Registering a callback

The miniport driver uses the IPortClsRuntimePower::RegisterPowerControlCallback method to register a callback. This method is invoked either when the PEP initiates a private request, or in response to a private request that is initiated by the miniport driver itself. The callback registration should typically be performed while the driver is handling the IRP_MN_START_DEVICE PNP Irp.

Aside from the Context pointer that is supplied in the callback, the other parameters are defined identically to the definitions for the runtime power framework’s PowerControlCallback. Additionally, the miniport’s callback must be of type PCPFNRUNTIME_POWER_CONTROL_CALLBACK, as defined in the following snippet from the Portcls.h header file.

typedef
NTSTATUS
_IRQL_requires_max_(DISPATCH_LEVEL)
(*PCPFNRUNTIME_POWER_CONTROL_CALLBACK)
(
    _In_        LPCGUID PowerControlCode,
    _In_opt_    PVOID   InBuffer,
    _In_        SIZE_T  InBufferSize,
    _Out_opt_   PVOID   OutBuffer,
    _In_        SIZE_T  OutBufferSize,
    _Out_opt_   PSIZE_T BytesReturned,
    _In_opt_    PVOID   Context
);

When the driver is stopped or removed, it must use the IPortClsRuntimePower::UnregisterPowerControlCallback method to unregister any registered callbacks.

Sending private power controls

After the miniport establishes access to an IPortClsRuntimePower interface, and uses the interface's RegisterPowerControlCallback method to register a callback, it is now ready to send private power controls. When the callback method is invoked, the miniport driver uses the IPortClsRuntimePower::SendPowerControl method to send the private power controls to the Windows PEP.

With the exception of the DeviceObject parameter, all other parameters are defined identically to those for the runtime power framework’s PoFxPowerControl method.