The data format of the host can have different endian characteristics than the data format of the device. In such a case, data transferred between the host and device would need to be byte-swapped to conform to the data format requirements of the destination location. Devices with the same endian characteristics of the host require no byte-swapping of the data.
Drivers specify the endian characteristics of the device by setting the appropriate flag in the ddi_device_acc_attr(9S) structure that is passed to ddi_regs_map_setup(9F). The DDI framework then performs any required byte-swapping when the driver calls a ddi_getX routine like ddi_get8(9F) or a ddi_putX routine like ddi_put16(9F) to read or write to device memory.