PCI DMA Address Access

Hi ,
We are writing a PCI driver for a device which has 28 bit
addressing , On read operation from the PCI device to the System memory
with the Scatter gather list generated using the DMA Adapter ,The
Elements list gives physical address in 32 bit address range, even after
the address translation before configuring the registers we are unable
to read the data .

But for the same when used with the common buffer created using the DMA
both read and write happens, but the common buffer which we create gives
the logical address with in 28 bit range. Is there is any special
consideration to be made in this situation or do we miss something apart
from address translation.