Chris Skepper wrote:

On Tue, 26 Aug 2008, Scott Wood wrote:

quoted

On Tue, Aug 26, 2008 at 01:00:05PM +0100, Chris Skepper wrote:

quoted

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?

There are some ethernet signals, a compact flash card detect, other LEDs 
and a push button also on port A.  Are those what you'd call 
non-memory-like?

Would any of them object to spurious reads, and writebacks of the value 
that was read?

quoted

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.

Where can I find out how to do that?  Since I have this board working 
with the old ARCH=ppc, can I copy anything from there?

See setup_cpm_bat in arch/powerpc/kernel/head_32.S.

Also, where would be a good place in the code to resume tracing?

As soon as you can set up a BAT -- though first, I would try just 
enabling the CPM debug console and see if you get anything from that.

-Scott