Early boot problem with MPC8247 and Linux 2.6.26

[Scott Wood]

On Tue, Aug 26, 2008 at 01:00:05PM +0100, Chris Skepper wrote:
> >How are you determining that it never gets to that point?  If it's via 
> >serial I/O or similar, be aware that I/O isn't going to work when caches 
> >are enabled but the MMU is not.
> 
> I'm triggering an LED which is connected to port A.  Are you saying that 
> wouldn't work once the caching is enabled?

It's quite possible.  What other registers are in the same cache line as
the LED, and are any of them non-memory-like?  And even if all registers
in the cache line are OK with this sort of access, you need to use dcbf
afterwards.

It's usually easiest to just trust that that part of the code works (in
my experience, that's rarely where a hang actually occurs when bringing
up a new board), and resume tracing after the MMU is on and you've
inserted a caching-inhibited BAT entry.

-Scott