[RFC/PATCH 0/3] Attempt at making 32bit BAT assignment more intelligent

[Grant Likely]

Here is my attempt to make BAT allocations dynamic instead of hard coded.
The first patch changes setbat() to dynamically assign BATs instead of requiring
the caller to select a BAT on its own.

A primary user of setbat is mmu_mapin_ram() which used to hard code BATs
2 and 3 for mapping as much of RAM as can fit in 2 BATs.  The first patch
changes the routine to try to use as many BATs as it needs to map all of RAM.
(Note: I've still got BAT0 reserved for mapping RAM, so even if lots of other
users of setbat() appear, RAM is guaranteed to be allocated at least 1 BAT).

The first patch also adds an ioremap_bat() function which works like
ioremap(), but uses BATs instead of page tables and can be called really
early (before MMU_init()).  ioremap_bat() mappings persist after MMU_init
is called too so it can be used to map all of an SoC's IMMR region, or
any other IO device for that matter.  I've seen about a 2.5% performance
improvement by using this on a simple network workload with SoC registers
BAT mapped.

The second patch is just a utility function required by the third patch.

The third patch is a new user of ioremap_bat() to implement early debug
support for the mpc5200 platform.

The first patch is the one I really want feedback on.  It shouldn't break
any 32 bit platforms, but I need testing to make sure.  Also, this is my
first attempt at messing with MMU code, so please let me know if I'm doing
anything foolish or dangerous.

Kumar, Josh; I'd appreciate testing to make sure patch 1 doesn't break stuff.

Thanks,
g.

--
Grant Likely, B.Sc. P.Eng.
Secret Lab Technologies Ltd.