For most I/O requests, the data buffer passed to the driver entry points is not accessed directly by the driver, it is just passed on to scsi_init_pkt(9F). If a driver sends SCSI commands that operate on buffers the driver examines itself (such as the SCSI request sense command), the buffers should be DMA consistent. The scsi_alloc_consistent_buf(9F) routine allocates a buf(9S) structure and a data buffer suitable for DMA-consistent operations. The HBA will perform any necessary synchronization of the buffer before performing the command completion callback.
scsi_alloc_consistent_buf(9F) uses scarce system resources; it should be used sparingly.