[PATCH 12/12] [POWERPC] 85xx: Add support for relocatble kernel (and booting at non-zero)

[Paul Mackerras]

Kumar Gala writes:

> Added support to allow an 85xx kernel to be run from a non-zero physical
> address (useful for cooperative asymmetric multiprocessing situations) and
> kdump.  The support can either be at compile time or runtime
> (CONFIG_RELOCATABLE).
> 
> Currently we are limited to running at a physical address that is module
> 256M.  This is due to how we map TLBs to cover lowmem and should be fixed
> up to allow 64M or maybe even 16M alignment in the future.

The first 11 patches look pretty reasonable, but I think I want a bit
more time to digest this one.  At the least it needs a bit more
description, saying for instance why you remove USER_PGD_PTRS and
KERNEL_PGD_PTRS (yes they are unused now but why does this patch need
to remove them?).  Also, given that we changed from using a
PPC_MEMSTART #define to a memstart_addr variable earlier in the patch
series, why do we need to change back to a #define (MEMORY_START) now?

I take it that with CONFIG_RELOCATABLE set, the kernel won't touch any
RAM below the point where it's loaded?  Is CONFIG_PHYSICAL_START used
at all if CONFIG_RELOCATABLE is set, and if so what does it mean?
What happens if CONFIG_KERNEL_START != CONFIG_PAGE_OFFSET and the
kernel is loaded at some address != CONFIG_PHYSICAL_START?

Are we sure that ARCH_PFN_OFFSET only gets applied to normal memory
pages, not any I/O?  What happens to /dev/mem when ARCH_PFN_OFFSET !=
0?

Also, since you're changing pmd_page(), it would be better to make it
use pfn_to_page or something similar rather than using mem_map + xxx.

Paul.