GPIO_CLIENT_STOP_CONTROLLER callback function (gpioclx.h)

Article
10/21/2021

The CLIENT_StopController event callback function performs operations that are needed to prepare the general-purpose I/O (GPIO) controller device to exit the D0 power state.

Syntax

GPIO_CLIENT_STOP_CONTROLLER GpioClientStopController;

NTSTATUS GpioClientStopController(
  [in] PVOID Context,
  [in] BOOLEAN SaveContext,
  [in] WDF_POWER_DEVICE_STATE TargetState
)
{...}

Parameters

[in] Context

A pointer to the GPIO controller driver's device context.

[in] SaveContext

Whether the client driver should save the current hardware context of the GPIO controller device. If TRUE, the hardware context should be saved. If FALSE, the hardware context should not be saved. For more information, see Remarks.

[in] TargetState

The target device power state. This parameter is a WDF_POWER_DEVICE_STATE enumeration value that specifies the low-power state that the device is to enter when it exits the D0 power state. The GPIO controller driver can use this information to determine how to configure the controller device before it leaves D0.

Return value

The CLIENT_StopController function returns STATUS_SUCCESS if the call is successful. Otherwise, it returns an appropriate error code.

Remarks

This callback function is implemented by the GPIO controller driver. The GPIO framework extension (GpioClx) calls this function to prepare the GPIO controller device to be turned off or to transition to a low-power state. This callback function must perform any operations that are necessary before the device enters a low-power state, such as saving any information that the driver will need later after the device is restored to the D0 power state.

Typically, the CLIENT_StopController callback function configures the GPIO pins to a platform-specific initial state. For example, this function might configure all of the GPIO pins as inputs to prevent output transients from occurring when the GPIO controller device is turned off.

To register your driver's CLIENT_StopController callback function, call the GPIO_CLX_RegisterClient method. This method accepts, as an input parameter, a pointer to a GPIO_CLIENT_REGISTRATION_PACKET structure that contains a CLIENT_StopController function pointer.

Although the CLIENT_StopController callback function is called at IRQL = PASSIVE_LEVEL, you should not make this function pageable. The CLIENT_StopController callback is in the critical timing path for restoring power to the devices in the hardware platform and, for performance reasons, it should not be delayed by page faults.

Examples

To define a CLIENT_StopController callback function, you must first provide a function declaration that identifies the type of callback function 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 CLIENT_StopController callback function that is named MyEvtGpioStopController, use the GPIO_CLIENT_STOP_CONTROLLER function type, as shown in this code example:

GPIO_CLIENT_STOP_CONTROLLER  MyEvtGpioStopController;

Then, implement your callback function as follows:

_Use_decl_annotations_
VOID
  MyEvtGpioStopController(
    PVOID Context,
    BOOLEAN RestoreContext,
    WDF_POWER_DEVICE_STATE TargetState
    )
{ ... }

The GPIO_CLIENT_STOP_CONTROLLER function type is defined in the Gpioclx.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 GPIO_CLIENT_STOP_CONTROLLER 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 KMDF Drivers. For more information about Use_decl_annotations, see Annotating Function Behavior.

Requirements

Requirement	Value
Minimum supported client	Supported starting with Windows 8.
Target Platform	Desktop
Header	gpioclx.h
IRQL	Called at PASSIVE_LEVEL.

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