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Protocols — PCI Bus Support
Version 1.10 12/01/02 12-23
Description
The Io.Read(), and Io.Write() functions enable a driver to access PCI controller registers in
the PCI root bridge I/O space.
The I/O operations are carried out exactly as requested. The caller is responsible for satisfying any
alignment and I/O width restrictions that a PCI root bridge on a platform might require. For
example on some platforms, width requests of EfiPciWidthUint64 do not work.
If Width is EfiPciWidthUint8, EfiPciWidthUint16, EfiPciWidthUint32, or
EfiPciWidthUint64, then both Address and Buffer are incremented for each of the
Count operations performed.
If Width is EfiPciWidthFifoUint8, EfiPciWidthFifoUint16,
EfiPciWidthFifoUint32, or EfiPciWidthFifoUint64, 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 EfiPciWidthFillUint8, EfiPciWidthFillUint16,
EfiPciWidthFillUint32, or EfiPciWidthFillUint64, 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 root bridge
.
EFI_INVALID_PARAMETER
Width is invalid for this PCI root bridge.
EFI_INVALID_PARAMETER
Buffer is NULL.
EFI_OUT_OF_RESOURCES The request could not be completed due to a lack of resources.