subsystem that the buffer is fully accessible at the elevated privilege
level (and ideally inaccessible or at least read-only at the
lesser-privileged levels).
-
-DMA_ATTR_OVERWRITE
-------------------
-
-This is a hint to the DMA-mapping subsystem that the device is expected to
-overwrite the entire mapped size, thus the caller does not require any of the
-previous buffer contents to be preserved. This allows bounce-buffering
-implementations to optimise DMA_FROM_DEVICE transfers.