Intel Extensible Firmware Interface - Manual (Page 439)

Protocols — PCI Bus Support
Version 1.10 12/01/02 12-21
Description
The Mem.Read() , and Mem.Write() functions enable a driver to access PCI controller
registers in the PCI root bridge memory space.
The memory operations are carried out exactly as requested. The caller is responsible for satisfying
any alignment and memory 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 read transactions generated by this function are guaranteed to be completed before
this function returns. All the PCI write transactions generated by this function will follow the
write ordering and completion rules defined in the PCI Specification. However, if the memory-
mapped I/O region being accessed by this function has the
EFI_PCI_ATTRIBUTE_MEMORY_CACHED attribute set, then the transactions will follow the
ordering rules defined by the processor architecture.
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.