Just out of curiosity where does this "interrupt-parent" property
come from?

On platforms I am familiar with, the parent path is walked to the root
and we stop at device nodes that have "interrupt-map" and
"interrupt-map-mask" properties.

"interrupt-parent" is defined in the Open Firmware "interrupt mapping"
recommended practice, the same place as "interrupt-map" etc. are.

The mechanism shown here seems overly simplistic and not able to  
handle
the cases handled by existing OF property schemes in use for several
years on real systems.

"interrupt-parent" is only meant to be used for the simple cases.  It's
quite handy there.  It is also required in all "interrupt-controller"
nodes that aren't the root of the interrupt tree.


Segher