# Foo subsystem/driver (a comment...)
Many methods in the "bus" interface are performing services for some child of the bus device. These methods would normally use the first two arguments to specify the bus providing the service and the child device which is requesting the service. To simplify driver code, many of these methods have accessor functions which lookup the parent and call a method on the parent. For instance the method `BUS_TEARDOWN_INTR(device_t dev, device_t child, ...)` can be called using the function `bus_teardown_intr(device_t child, ...)`.