Openfirmware bus driver

[Andrew Turner]

For my work on porting FreeBSD to the EFIKA I've written a generic
Open Firmware bus [1]. It is based on the PowerPC nexus device and has
been tested on a PowerPC machine. With it, devices that attach to an
Open Firmware node can attach to the bus rather than searching the
Open Firmware tree on it's own.

With some more work the bus can replace the Open Firmware parts of the
PowerPC, Sparc64 and Sun4v nexus buses.

Andrew

[1] http://fubar.geek.nz/files/freebsd/ofwbus.c