Intel Extensible Firmware Interface - Manual (Page 443)

Protocols — PCI Bus Support
Version 1.10 12/01/02 12-25
Description
The Pci.Read() and Pci.Write() functions enable a driver to access PCI configuration
registers for a PCI controller.
The PCI Configuration operations are carried out exactly as requested. The caller is responsible for
any alignment and PCI configuration width issues 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.
Table 12-1. PCI Configuration Address
Mnemonic Byte
Offset Byte
Length
Description
Register 0 1 The register number on the PCI Function.
Function 1 1 The PCI Function number on the PCI Device.
Device 2 1 The PCI Device number on the PCI Bus.
Bus 3 1 The PCI Bus number.
ExtendedRegister 4 4 The register number on the PCI Function. If this field is zero,
then the Register field is used for the register number. If this
field is nonzero, then the Register field is ignored, and the
ExtendedRegister field is used for the register number.
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.