Purpose of PCI address in ranges property

[valmiki <valmikibow@xxxxxxxxx>]

Hi,

When ranges property is being parsed using 
of_pci_get_host_bridge_resources, the pci address is being used for
calculating the offset for pci_add_resource_offset.

What is this offset for ?

So the cpu address is being used for programming memory base and limit 
registers ?

Thanks & Regards,
Valmiki