phandle property uniqueness

[andreeaflorescu]

The phandle property can be used to reference another node within the FDT uniquely: https://devicetree-specification.readthedocs.io/en/stable/devicetree-basics.html?#phandle

Right now we are not checking the uniqueness of the phandle, and I think there are a few things that we can do:

• create a public API for retrieving a unique phandle, similar to what is implemented in libfdt: https://github.com/torvalds/linux/blob/5bfc75d92efd494db37f5c4c173d3639d4772966/scripts/dtc/libfdt/fdt_ro.c#L114
• add support for the phandle property; we could for example offer an API for setting the phandle of a node (once we clean up the abstractions to have a clear ownership between nodes & properties), and in the set function we can check for uniqueness. This would imply denying adding properties with the name phandle, or just check the name of the property, and in case it is phandle, check for uniqueness. It looks like this adds branching in the code, and we should discuss if we just want to go ahead with documenting this, or enforcing it.

[andreeaflorescu]

Fixed by #47