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defxx: Add missing DMA synchronisation calls
This adds DMA synchronisation calls needed in the receive path: 1. To retrieve the Receive Status word that is prepended by the PDQ DMA engine in the receive buffer, and provides information about the frame received, including its size and any errors. 2. To make data received available for copying in the small-frame case (size <= SKBUFF_RX_COPYBREAK) where the original DMA buffer will be returned to the receive descriptor ring and therefore its mapping retained. With DMA mapping error handling in place, added by the other patch, this may now also trigger where an attempt to map a newly allocated buffer for DMA has failed. In that case data from the original buffer will be copied out and the buffer returned to the DMA descriptor ring. These calls may do nothing when data is in the host DMA addressing range of the FDDI interface, such as always on 32-bit systems, however their absence makes frame reception stop functioning reliably on systems that have memory beyond the low 4GB of the address space. Reported-by:Robert Coerver <Robert.Coerver@ll.mit.edu> Tested-by: