Soft State Structure

The driver should allocate the per-device-instance soft state structure, being careful to clean up properly if an error occurs.

instance = ddi_get_instance(dip);
 if (ddi_soft_state_zalloc(isp_state,
 		instance) != DDI_SUCCESS) {
 	return (DDI_FAILURE);
 }
 isp = ddi_get_soft_state(isp_state, instance);