David Miller writes:

On sparc platforms this is obtained differently.  We obtain the 32-bit
instance value of "/chosen/stdout" and convert that into a prom device
node path using "instance-to-path".

That's actually exactly what we do too, the linux,stdout-path property
is just a cache of the result of that process.  The difference is that
we have to do it early on while we still have OF around, while you can
do it later.

Paul.