Intel Extensible Firmware Interface - Manual (Page 247)

Protocols — EFI Driver Model
Version 1.10 12/01/02 9-5
CloseProtocol() . Since ControllerHandle may have been previously started by the
same driver, if a protocol is already in the opened state, then it must not be closed with
CloseProtocol() . This is required to guarantee the state of ControllerHandle is not
modified by this function.
If any of the protocol interfaces on the device specified by ControllerHandle that are required
by the driver specified by This are already open for exclusive access by a different driver or
application, then EFI_ACCESS_DENIED is returned.
If any of the protocol interfaces on the device specified by ControllerHandle that are required
by the driver specified by This are already opened by the same driver, then
EFI_ALREADY_STARTED is returned. However, if the driver specified by This is a bus driver
that is able to create one child handle at a time, then it is not an error, and the bus driver should
continue with its test of
ControllerHandle . This allows a bus driver to create one child
handle on the first call to Supported() and Start() , and create additional child handles on
additional calls to Supported() and Start() .
If ControllerHandle is not supported by This , then EFI_UNSUPPORTED is returned.
If This is a bus driver that creates child handles with an EFI_DEVICE_PATH_PROTOCOL , then
ControllerHandle must support the EFI_DEVICE_PATH . If it does not, then
EFI_UNSUPPORTED is returned.
If ControllerHandle is supported by This , and This is a device driver, then
EFI_SUCCESS is returned.
If ControllerHandle is supported by This , and This is a bus driver, and
RemainingDevicePath is NULL , then EFI_SUCCESS is returned.
If ControllerHandle is supported by This , and This is a bus driver, and
RemainingDevicePath is not NULL , then RemainingDevicePath must be analyzed. If
RemainingDevicePath starts with an EFI Device Path node that the bus driver recognizes and
supports, then EFI_SUCCESS is returned. Otherwise, EFI_UNSUPPORTED is returned.
The Supported() function is designed to be invoked from the EFI boot service
ConnectController() . As a result, much of the error checking on the parameters to
Supported() has been moved into this common boot service. It is legal to call Supported()
from other locations, but the following calling restrictions must be followed or the system behavior
will not be deterministic.
ControllerHandle must be a valid EFI_HANDLE . If RemainingDevicePath is not
NULL , then it must be a pointer to a naturally aligned EFI_DEVICE_PATH that contains at least
one device path node other than the end node.