Intel Extensible Firmware Interface, Specification

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Device I/O Protocol
Version 1.02 12/12/00 139
Description
The
DEVICE_IO
protocol provides the basic Memory, I/O, and PCI interfaces that are used to
abstract accesses to devices.
A driver that controls a physical device obtains the proper
DEVICE_IO
protocol interface by
checking for the supported protocol on the programmatic parent(s) for the device. This is easily
done via the
LocateDevicePath()
function.
The following C code fragment illustrates the use of the
DEVICE_IO
protocol:
// Get the handle to our parent that provides the device I/O
// protocol interfaces to “
MyDevice ” (which has the device path
// of “ MyDevicePath ”)
EFI_DEVICE_IO_INTERFACE * IoFncs ;
EFI_DEVICE_PATH *SearchPath;
SearchPath = MyDevicePath ;
Status = LocateDevicePath (
&DeviceIoProtocol, // Protocol GUID
&SearchPath, // Device Path SearchKey
& DevHandle // Return EFI Handle
);
// Get the device I/O interfaces from the handle
Status = HandleProtocol (
DevHandle , &DeviceIoProtocol, & IoFncs );
// Read 1 dword into Buffer from MyDevice’s I/O address
IoFncs ->Io.Read ( IoFncs , IO_UINT32, MyDeviceAddress , 1, &Buffer);
The call to
LocateDevicePath()
takes the Device Path of a device and returns the handle that
contains the
DEVICE_IO
protocol for the device. The handle is passed to
HandleProtocol()
with a pointer to the
EFI_GUID
for
DEVICE_IO
protocol and a pointer to the
DEVICE_IO
protocol is returned. The
DEVICE_IO
protocol pointer
IoFncs
is then used to do an I/O read to
a device.