Intel Extensible Firmware Interface - Manual (Page 258)

Extensible Firmware Interface Specification
9-16 12/01/02 Version 1.10
e. Call OpenProtocol() on behalf of the child C with an Attribute of
EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER .
8. END FOR
9. END IF
10. Return EFI_SUCCESS .
Listed below is sample code of the Start() function of a device driver for a device on the XYZ
bus. The XYZ bus is abstracted with the EFI_XYZ_IO_PROTOCOL . This driver does allow the
EFI_XYZ_IO_PROTOCOL to be shared with other drivers, and just the presence of the
EFI_XYZ_IO_PROTOCOL on ControllerHandle is enough to determine if this driver
supports ControllerHandle . This driver installs the EFI_ABC_IO_PROTOCOL on
ControllerHandle . The gBS variable is initialized in this driver’s entry point as shown in the
EFI Driver Model examples in Chapter 4.
extern EFI_GUID gEfiXyzIoProtocol;
extern EFI_GUID gEfiAbcIoProtocol;
EFI_BOOT_SERVICES_TABLE *gBS;
EFI_STATUS
AbcStart (
IN EFI_DRIVER_BINDING_PROTOCOL *This,
IN EFI_HANDLE ControllerHandle,
IN EFI_DEVICE_PATH_PROTOCOL *RemainingDevicePath OPTIONAL
)
{
EFI_STATUS Status;
EFI_XYZ_IO_PROTOCOL *XyzIo;
EFI_ABC_DEVICE AbcDevice;
//
// Open the Xyz I/O Protocol that this driver consumes
//
Status = gBS->OpenProtocol (
ControllerHandle,
&gEfiXyzIoProtocol,
&XyzIo,
This->DriverBindingHandle,
ControllerHandle,
EFI_OPEN_PROTOCOL_BY_DRIVER
);
if (EFI_ERROR (Status)) {
return Status;
}
//
// Allocate and zero a private data structure for the Abc device.
//
Status = gBS->AllocatePool (
EfiBootServicesData,
sizeof (EFI_ABC_DEVICE),
&AbcDevice
);