Intel Extensible Firmware Interface - Manual (Page 490)

Extensible Firmware Interface Specification
12-72 12/01/02 Version 1.10
Description
The Io.Read() , and Io.Write() functions enable a driver to access PCI controller registers in
PCI I/O space.
The I/O operations are carried out exactly as requested. The caller is responsible for any alignment
and I/O width issues which the bus, device, platform, or type of I/O might require. For example on
some platforms, width requests of
EfiPciIoWidthUint64 do not work.
If Width is EfiPciIoWidthUint8 , EfiPciIoWidthUint16 , EfiPciIoWidthUint32 ,
or EfiPciIoWidthUint64 , then both Address and Buffer are incremented for each of the
Count operations performed.
If Width is EfiPciIoWidthFifoUint8 , EfiPciIoWidthFifoUint16 ,
EfiPciIoWidthFifoUint32 , or EfiPciIoWidthFifoUint64 , then only Buffer is
incremented for each of the Count operations performed. The read or write operation is
performed Count times on the same Address .
If Width is EfiPciIoWidthFillUint8 , EfiPciIoWidthFillUint16 ,
EfiPciIoWidthFillUint32 , or EfiPciIoWidthFillUint64 , then only Address is
incremented for each of the Count operations performed. The read or write operation is
performed Count times from the first element of Buffer .
All the PCI transactions generated by this function are guaranteed to be completed before this
function returns.
Status Codes Returned
EFI_SUCCESS The data was read from or written to the PCI controller .
EFI_INVALID_PARAMETER Width is invalid.
EFI_INVALID_PARAMETER Buffer is NULL .
EFI_UNSUPPORTED BarIndex not valid for this PCI controller.
EFI_UNSUPPORTED The address range specified by Offset , Width , and Count is not
valid for the PCI BAR specified by BarIndex .
EFI_OUT_OF_RESOURCES The request could not be completed due to a lack of resources.