DMA deals with Physical addresses.
Only when CPU accesses addresses it refers to MMU(Memory Management Unit) and MMU converts the Physical address to Virtual address.
But, DMA controller is a device which directly drives the data and address bus during data transfer. So, it is purely Physical address. (It never needs to go through MMU & Virtual addresses).
That is why when writing the device drivers, the physical address of the data buffer has to be assigned to the DMA.

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