where should readb based/platform specific memcpy_fromio() be?

[Yasushi SHOJI]

Hello,

I'd like to add a variant of memcpy_fromio() for 16bit bus.  In-tree
implementations seem to me that most, if not all, arch have either
readb() or memcpy() based mempy_fromio.

powerpc doesn't currently have readb() based.  I assume that means all
ppc boards are 32bit clean.

if I'd like merge this readb() based or optimized for 16bit bus
version, where should I put it?  obviously I have to add ifdef in
include/asm-ppc/io.h, but should I do either:

  - add extern in io.h and body under platform/..../xxxx.c
  - add extern in io.h and body under arch/ppc/lib/io.c
  - add static inline version in io.h
  - add static inline version in platform/..../xxxxx.h which is
    included from asm-ppc/io.h

regards,
--
         yashi