The function value is the final status from the operation.

--*/
{
    NTSTATUS ntStatus = STATUS_SUCCESS;
    PDEVICE_EXTENSION deviceExtension;
    PIRP pIrp = NULL;

    deviceExtension =  DeviceObject->DeviceExtension;

    // This should have been reset in completion routine
    ISOUSB_ASSERT( !deviceExtension->SelfPowerIrp );

    if (  deviceExtension->CurrentDevicePowerState ==  PowerState.DeviceState )
        return STATUS_SUCCESS;  // nothing to do

    ISOUSB_KdPrint( DBGLVL_HIGH,("Enter IsoUsb_SelfRequestPowerIrp() will request power irp to state %s\n",
        ISOUSB_StringForDevState( PowerState.DeviceState )));

    IsoUsb_IncrementIoCount(DeviceObject);

	// flag we're handling a self-generated power irp
    deviceExtension->SelfPowerIrp = TRUE;

	// actually request the Irp
    ntStatus = PoRequestPowerIrp(deviceExtension->PhysicalDeviceObject, 
                         IRP_MN_SET_POWER,
                         PowerState,
                         IsoUsb_PoSelfRequestCompletion,
                         DeviceObject,
                         NULL);


    if  ( ntStatus == STATUS_PENDING ) { 
        // status pending is the return code we wanted

        // We only need to wait for completion if we're powering up
        if ( (ULONG) PowerState.DeviceState < deviceExtension->PowerDownLevel ) {

            NTSTATUS waitStatus;

            waitStatus = KeWaitForSingleObject(
                           &deviceExtension->SelfRequestedPowerIrpEvent,
                           Suspended,
                           KernelMode,
                           FALSE,
                           NULL);

        }

        ntStatus = STATUS_SUCCESS;

        deviceExtension->SelfPowerIrp = FALSE;

        ISOUSB_KdPrint( DBGLVL_HIGH, ("IsoUsb_SelfRequestPowerIrp() SUCCESS\n    IRP 0x%x to state %s\n",
            pIrp, ISOUSB_StringForDevState(PowerState.DeviceState) ));


    }
    else {
        // The return status was not STATUS_PENDING; any other codes must be considered in error here;
        //  i.e., it is not possible to get a STATUS_SUCCESS  or any other non-error return from this call;
        ISOUSB_KdPrint( DBGLVL_HIGH, ("IsoUsb_SelfRequestPowerIrp() to state %s FAILED, status = 0x%x\n",
            ISOUSB_StringForDevState( PowerState.DeviceState ),ntStatus));
    }

    return ntStatus;
}



NTSTATUS
IsoUsb_PoSelfRequestCompletion(
    IN PDEVICE_OBJECT       DeviceObject,
    IN UCHAR                MinorFunction,
    IN POWER_STATE          PowerState,
    IN PVOID                Context,
    IN PIO_STATUS_BLOCK     IoStatus
    )
/*++

Routine Description:

    This routine is called when the driver completes a self-originated power IRP 
	that was generated by a call to IsoUsb_SelfSuspendOrActivate().
    We power down whenever the last pipe is closed and power up when the first pipe is opened.

    For power-up , we set an event in our FDO extension to signal this IRP done
    so the power request can be treated as a synchronous call.
    We need to know the device is powered up before opening the first pipe, for example.
    For power-down, we do not set the event, as no caller waits for powerdown complete.

Arguments:

    DeviceObject - Pointer to the device object for the class device. ( Physical Device Object )

    Context - Driver defined context, in this case our FDO ( functional device object )

Return Value:

    The function value is the final status from the operation.

--*/
{
    PDEVICE_OBJECT deviceObject = Context;
    PDEVICE_EXTENSION deviceExtension = deviceObject->DeviceExtension;
    NTSTATUS ntStatus = IoStatus->Status;

    // we should not be in the midst of handling a system-generated power irp
    ISOUSB_ASSERT( NULL == deviceExtension->PowerIrp );

    // We only need to set the event if we're powering up;
    // No caller waits on power down complete
    if ( (ULONG) PowerState.DeviceState < deviceExtension->PowerDownLevel ) {

        // Trigger Self-requested power irp completed event;
        //  The caller is waiting for completion
        KeSetEvent(&deviceExtension->SelfRequestedPowerIrpEvent, 1, FALSE);
    }

    IsoUsb_DecrementIoCount(deviceObject);

    ISOUSB_KdPrintCond( DBGLVL_HIGH, !NT_SUCCESS(ntStatus),("Exit IsoUsb_PoSelfRequestCompletion() FAILED, ntStatus = 0x%x\n", ntStatus ));
   
    return ntStatus;
}


BOOLEAN
IsoUsb_SetDevicePowerState(
    IN PDEVICE_OBJECT DeviceObject,
    IN DEVICE_POWER_STATE DeviceState
    )
/*++

Routine Description:

    This routine is called when An IRP_MN_SET_POWER of type 'DevicePowerState'
    has been received by IsoUsb_ProcessPowerIrp().


Arguments:

    DeviceObject - Pointer to the device object for the class device.

    DeviceState - Device specific power state to set the device in to.


Return Value:

    For requests to DeviceState D0 ( fully on ), returns TRUE to signal caller 
    that we must set a completion routine and finish there.

--*/
{
    NTSTATUS ntStatus = STATUS_SUCCESS;
    PDEVICE_EXTENSION deviceExtension;
    BOOLEAN fRes = FALSE;

    deviceExtension = (PDEVICE_EXTENSION) DeviceObject->DeviceExtension;

    switch (DeviceState) {
    case PowerDeviceD3:

        //
        // Device will be going OFF, 
		// TODO: add any needed device-dependent code to save state here.
		//  ( We have nothing to do in this sample )
        //

        ISOUSB_KdPrint( DBGLVL_MEDIUM,("IsoUsb_SetDevicePowerState() PowerDeviceD3 (OFF)\n"));

        deviceExtension->CurrentDevicePowerState = DeviceState;
        break;

    case PowerDeviceD1:
    case PowerDeviceD2:
        //
        // power states D1,D2 translate to USB suspend

        ISOUSB_KdPrint( DBGLVL_MEDIUM,("IsoUsb_SetDevicePowerState()  %s\n",
            ISOUSB_StringForDevState(DeviceState) ));

        deviceExtension->CurrentDevicePowerState = DeviceState;
        break;

    case PowerDeviceD0:


        ISOUSB_KdPrint( DBGLVL_MEDIUM,("IsoUsb_SetDevicePowerState() PowerDeviceD0 (ON)\n"));

        // We'll need to finish the rest in the completion routine;
        //   signal caller we're going to D0 and will need to set a completion routine
        fRes = TRUE;

        // Caller will pass on to PDO ( Physical Device object )
        break;

    default:

        ISOUSB_KdPrint( DBGLVL_MEDIUM,(" Bogus DeviceState = %x\n", DeviceState));
    }

    return fRes;
}



NTSTATUS
IsoUsb_QueryCapabilities(
    IN PDEVICE_OBJECT PdoDeviceObject,
    IN PDEVICE_CAPABILITIES DeviceCapabilities
    )

/*++

Routine Description:

    This routine generates an internal IRP from this driver to the PDO
    to obtain information on the Physical Device Object's capabilities.
    We are most interested in learning which system power states
    are to be mapped to which device power states for honoring IRP_MJ_SET_POWER Irps.

    This is a blocking call which waits for the IRP completion routine
    to set an event on finishing.

Arguments:

    DeviceObject        - Physical DeviceObject for this USB controller.

Return Value:

    NTSTATUS value from the IoCallDriver() call.

--*/

{
    PIO_STACK_LOCATION nextStack;
    PIRP irp;
    NTSTATUS ntStatus;
    KEVENT event;


    // This is a DDK-defined DBG-only macro that ASSERTS we are not running pageable code
    // at higher than APC_LEVEL.
    PAGED_CODE();


    // Build an IRP for us to generate an internal query request to the PDO
    irp = IoAllocateIrp(PdoDeviceObject->StackSize, FALSE);

    if (!irp) {
        return STATUS_INSUFFICIENT_RESOURCES;
    }


    // IoGetNextIrpStackLocation gives a higher level driver access to the next-lower
    // driver's I/O stack location in an IRP so the caller can set it up for the lower driver.
    nextStack = IoGetNextIrpStackLocation(irp);
    ISOUSB_ASSERT(nextStack != NULL);
    nextStack->MajorFunction= IRP_MJ_PNP;
    nextStack->MinorFunction= IRP_MN_QUERY_CAPABILITIES;

    // init an event to tell us when the completion routine's been called
    KeInitializeEvent(&event, NotificationEvent, FALSE);

    // Set a completion routine so it can signal our event when
    //  the next lower driver is done with the Irp
    IoSetCompletionRoutine(irp,
                           IsoUsb_IrpCompletionRoutine,
                           &event,  // pass the event as Context to completion routine
                           TRUE,    // invoke on success
                           TRUE,    // invoke on error
                           TRUE);   // invoke on cancellation of the Irp


    // set our pointer to the DEVICE_CAPABILITIES struct
    nextStack->Parameters.DeviceCapabilities.Capabilities = DeviceCapabilities;

    ntStatus = IoCallDriver(PdoDeviceObject,
                            irp);

    ISOUSB_KdPrint( DBGLVL_MEDIUM,(" IsoUsb_QueryCapabilities() ntStatus from IoCallDriver to PCI = 0x%x\n", ntStatus));

    if (ntStatus == STATUS_PENDING) {
       // wait for irp to complete

       KeWaitForSingleObject(
            &event,
            Suspended,
            KernelMode,
            FALSE,
            NULL);
    }

    // failed? this is probably a bug
    ISOUSB_KdPrintCond( DBGLVL_DEFAULT,(!NT_SUCCESS(ntStatus)), ("IsoUsb_QueryCapabilities() failed\n"));

    IoFreeIrp(irp);

    return ntStatus;
}