undefined reference to pci_io_base

[Geoff Levand <geoffrey.levand@am.sony.com>]

I'm trying to understand the intended design of the inb()
and outb() macros in asm-powerpc/io.h. They are causing
me some grief when I set CONFIG_PCI=n:

  drivers/built-in.o: undefined reference to `pci_io_base'

This is coming from drivers/char/mem.c, which is always
built in, and is referencing pci_io_base through inb()
and outb().

Anyway, it seems asm-powerpc/io.h has two sets of io macros,
one set for iSeries, and one generic set for everything else.
The problem arises because the generic macros just use the eeh
macros in eeh.h, which in turn, directly use pci_io_base. 

I can think of three solutions to this that work for me, but
I'm not sure which, if any, would be the most proper.  One
would be to just have this in io.h:

  #if defined(CONFI_PCI)
  extern unsigned long pci_io_base;
  #else
  #define pci_io_base 0
  #endif

Another would be to have this in some file that is always built
in, like setup-common.c:

  #if !defined(CONFI_PCI)
  unsigned long pci_io_base;
  EXPORT_SYMBOL(pci_io_base);
  #endif

A third would be to have another set of io macros in io.h that
are used when CONFIG_PCI=n.

Comments welcome.

-Geoff