Each descriptor is 256 bits wide, the first 128 bits store the descriptor information and the next 128 bits provide a pointer to the next descriptor. In this mode, the descriptor can be located anywhere in the memory (it might not be in the same 4K page).
Further details are shown in Table: Buffer Descriptor Format in Linked-list Descriptor Mode.
•Each descriptor is 256 bits wide
•Each descriptor must be 256-bit aligned
•The descriptor element type is always 1 (in link-list descriptor mode)
•DMA channel can only fetch the next descriptor if it has read a current descriptor. Two descriptor fetches requires two AXI reads.