All programmed I/O (PIO) access by a hardened driver must use Solaris DDI access functions from the ddi_getX, ddi_putX, ddi_rep_getX, and ddi_rep_putX families of routines. The driver should not directly access the mapped registers by the address returned from ddi_regs_map_setup(9F). Using an access handle ensures that an I/O fault is controlled and its effects confined to the returned value, rather than possibly corrupting other parts of the machine state. (Avoid the ddi_peek(9F) and ddi_poke(9F) routines because they do not use access handles.)
The DDI access mechanism is important because it provides an opportunity to control how data is read into the kernel. DDI access routines provide protection by constraining the effect of bus timeout traps.