Intel Extensible Firmware Interface User Manual
Page 249
Protocols
— EFI Driver Model
Version 1.10
12/01/02
9-7
//
// EXAMPLE #2
//
// The RemainingDevicePath parameter can be used to initialize only
// the minimum devices required to boot. For example, maybe we only
// want to initialize 1 hard disk on a SCSI channel. If DriverImageHandle
// is a SCSI Bus Driver, and ControllerHandle is a SCSI Controller, and
// we only want to create a child handle for PUN=3 and LUN=0, then the
// RemainingDevicePath would be SCSI(3,0)/END. The following example
// would return EFI_SUCCESS if the SCSI driver supports creating the
// child handle for PUN=3, LUN=0. Otherwise it would return an error.
//
Status = DriverBinding->Supported (
DriverBinding,
ControllerHandle,
RemainingDevicePath
);
return Status;
Pseudo Code
Listed below are the algorithms for the
function for three different types of
drivers. How the
function of a driver is implemented can affect how the
Supported()
function is implemented. All of the services in the
need to work together to make sure that all resources
opened or allocated in
Supported()
and
Start()
are released in
The first algorithm is a simple device driver that does not create any additional handles. It only
attaches one or more protocols to an existing handle. The second is a bus driver that always creates
all of its child handles on the first call to
Start()
. The third is a more advanced bus driver that
can either create one child handles at a time on successive calls to
Start()
, or it can create all of
its child handles or all of the remaining child handles in a single call to
Start()
.
Device Driver:
1. Ignore the parameter
RemainingDevicePath
.
2. Open all required protocols with
. A standard driver should use an
Attribute
of
EFI_OPEN_PROTOCOL_BY_DRIVER
. If this driver needs exclusive access
to a protocol interface, and it requires any drivers that may be using the protocol interface to
disconnect, then the driver should use an
Attribute
of
EFI_OPEN_PROTOCOL_BY_DRIVER | EFI_OPEN_PROTOCOL_EXCLUSIVE
.
3. If any of the calls to
OpenProtocol()
in (2) returned an error, then close all of the protocols
opened in (2) with
, and return the status code from the call to
OpenProtocol()
that returned an error.
4. Use the protocol instances opened in (2) to test to see if this driver supports the controller.
Sometimes, just the presence of the protocols is enough of a test. Other times, the services of
the protocols opened in (2) are used to further check the identity of the controller. If any of
these tests fails, then close all the protocols opened in (2) with
CloseProtocol()
and
return
EFI_UNSUPPORTED
.
5. Close all protocols opened in (2) with
CloseProtocol()
.
6. Return
EFI_SUCCESS
.