[RFC] FLATMEM: allow memory to start at pfn != 0

[Franck Bui-Huu <vagabon.xyz@gmail.com>]

This patchset relaxes this constraint. Basically you just need to
define in your platform code (include/asm-mips/mach-foo/spaces.h
probably) PHYS_OFFSET that corresponds to the start of your
physical memory and you're done.

The first patch is just a fix for HIGHMEM, I just found it while
writing this patchset. I haven't done any tests though, I have
no hardwares to play with.

The second and third patchs are the real meat. There are 2 points
that I'm not really sure:

	- PHYS_OFFSET is defined in page.h, I'm not sure if it's
	the right place though.

	- ARCH_PFN_OFFSET is always defined whatever the memory
	model. I don't think it will hurt since physical memory
	always has a starting point in all cases.



Please consider.

		Franck
---

 arch/mips/kernel/setup.c |   30 ++++++++++++++++++++++--------
 arch/mips/mm/init.c      |   30 +++++++++++++-----------------
 include/asm-mips/dma.h   |    1 +
 include/asm-mips/io.h    |    4 ++--
 include/asm-mips/page.h  |   25 +++++++++++++++++++++----
 5 files changed, 59 insertions(+), 31 deletions(-)