RMO ? (in the prom_init.c)

[HongWoo Lee]

Hi ~

Can anybody tell me what the RMO is ?? in the linux kernel. 
(arch/powerpc/kernel/prom_init.c)
Through googling and guessing, I found "Read Memory Only" and "Relaxed 
Memory Order".
But none of these are not properly understood in the context.

Thanks in advance.

HongWoo.