What does DMA Channel virtualization mean?

Question

Hi I have seen documents in which DMA is working on the physical addresses. In that The DMA controller is actually using physical address to access the FIFOs. In a recent discussion a question came up that when we implement a driver for DMA whether this will work on physical address or virtual address. In the discussion the term DMA Channel virtualization also came up. Does this have anything to do with Virtual addressing as such. or DMA does not use virtual addressing at all.

Answer 1

Many devices these days come with iommu. This allows the paltform to create a virtual address space for the peripheral bus. This can be used for virtalization and is also useful for DMA when copying a large set of scattered memory pages without supporting scatter gather.