OFWBUS: How does autoconfiguration work?

I am interested in adding autoconfiguration to one of my projects.
The current drivers use lazy initialization, for example, the UART
drivers initialize the hardware only during their first invocation.

I would like to add a subsystem, that will read the DTB and call
the appropriate drivers.

I want to know how it is implemented in FreeBSD, I took a look at the
code, but I am still couldn't figure out, when does FreeBSD start to
parse the DTB, how does it fill up the device struct and few more.

Can someone please explain how all this works with reference to code
or point me to some documentation?

Thanks,
Niteesh