[Bug 33854] Compile fails with CONFIG_NOHIGHMEM=y

[Cafuego]

Public bug reported:
https://launchpad.net/malone/bugs/33854

Affects: linux-source-2.6.15 (Ubuntu)
       Severity: Normal
       Priority: (none set)
         Status: Unconfirmed

Description:
When custom-compiling this source tree I noticed compilation fails when
HIGHMEM is disabled. I expect enabling CONFIG_NOHIGHMEM should
automatically also enable CONFIG_1GB.

I checked include/asm/page_offset.h and notice that there is no fall-
through case in the page offset defines. Thus with CONFIG_NOHIGHMEM=y
PAGE_OFFSET_RAW ends up not being defined at all.

Fixes:
1) Force the choice of CONFIG_NOHIGHMEM to set a suitable default "User address space size" or
2) Patch include/asm/page_offset.h to allow a fall-through case.

The actual error message:

cafuego at cachaca:/usr/src/linux-source-2.6.15-2.6.15$ make
  CHK     include/linux/version.h
  SPLIT   include/linux/autoconf.h -> include/config/*
  CC      arch/i386/kernel/asm-offsets.s
  GEN     include/asm-i386/asm-offsets.h
  CC      init/main.o
In file included from include/asm/dma.h:13,
                 from include/linux/bootmem.h:8,
                 from init/main.c:30:
include/asm/io.h: In function ‘virt_to_phys’:
include/asm/io.h:78: error: ‘PAGE_OFFSET_RAW’ undeclared (first use in this function)
include/asm/io.h:78: error: (Each undeclared identifier is reported only once
include/asm/io.h:78: error: for each function it appears in.)
include/asm/io.h: In function ‘phys_to_virt’:
include/asm/io.h:96: error: ‘PAGE_OFFSET_RAW’ undeclared (first use in this function)
In file included from init/main.c:45:
include/linux/efi.h: In function ‘efi_range_is_wc’:
include/linux/efi.h:315: error: ‘PAGE_OFFSET_RAW’ undeclared (first use in this function)
In file included from include/linux/rmap.h:10,
                 from init/main.c:47:
include/linux/mm.h: In function ‘lowmem_page_address’:
include/linux/mm.h:512: error: ‘PAGE_OFFSET_RAW’ undeclared (first use in this function)
make[1]: *** [init/main.o] Error 1
make: *** [init] Error 2