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DDI 8 allows DMA access
to any part of memory, including that above 4GB.
Earlier DDI versions
prevented drivers from accessing memory above 4GB
because physical addresses were exposed
as the 32-bit unsigned paddr_t
data type.
In DDI 8, all references to physical addresses are eliminated except for the following two forms:
paddr32_t
type.
64-bit scatter/gather lists can represent
64-bit addresses from two paddr32_t
fields.