SoC emulation: what is the purpose of object_property_add_child that adds SoC device as a child of MachineState?

[Alyosha Shevandin]

I had looked over the implementations of SoC emulation. SoC emulation is usually implemented as object that is derived from DeviceState. It is common to connect the SoC object to the MachineState object as a child, for instance ../hw/arm/orangepi.c, line 57:

object_property_add_child(OBJECT(machine),"soc", OBJECT(h3));

What purpose does it serve?