PLX 9054 PCI bridge driver

Hello all,

I am planning to write host bridge driver for PLX PCI 9054 bridge.
So, I have started reading PCI implementation in Linux.  While reading the
sources,
I could not clearly understand the significance and use of the following
macros and variables.

	_IO_BASE
	_ISA_MEM_BASE
	PCI_DRAM_OFFSET
	isa_io_base
	isa_mem_base
	pci_dram_offset

Can anyone help me in this regard.  Any kind of help is greatly appreciated.
Thank you in advance.
I had prior experience with Linux frame buffer drivers.

-RK

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