class Child(Elaboratable):
	def __init__(self):
		self.bus = Interface(bus_signature)

	# ...

class Parent(Elaboratable):
	def __init__(self):
		self.bus = Interface(bus_signature)

	def elaborate(self, platform):
		m = Module()

		m.submodules.child = Child()

		# How to connect self.bus to m.child.bus?