dma - when can we use memory-to-memory ?

Hello, I have fpga connected to cpu. In fpga we implement fifo which the cpu need to write into or read from. The fpga is used for mac implementation. So we actually need to copy to/from ip stack buffer to the fifo buffers in fpga. As far as I understand this is memory-to-memory dma. But I am not sure because maybe it should be treated as memoty-device ? Is there any idea what is the correct way of treating this in kernel dma ? regards, Ran