Debugging kernel on mpc7448

[Cajus Pollmeier <cajus@naasa.net>]

Hello there,

I'm currently trying to get a kernel upgrade from 2.6.11 to 2.6.31
working with u-boot/cuImage.c2k on a custom marvell discovery 3 board.
In the moment, the following steps work:

* u-boot (1.1.4, not changeable in the moment) runs from flash and
offers a prompt
* loading cuImage.c2k
* running the code of wrapper.c until calling vmlinux.addr
* entering __start in head_32.S and running until early_init gets called

The systems then hangs until the watchdog resets the board. In this
early stage, I've no output to the serial console - which is the only
way to see what's going on there without having a development board with
single step capabilities.

To track it until early_init, I tried to place a stupid "blr" in
head_32.S, in order to get back to wrapper.c - which writes out a
message to the serial console in case the kernel "accidently" gets back
to it.

>From now on, I'm not sure if early_init is properly called. The blr
after the call is either not reached or there's something going on which
is beyond my limited knowledge of ppc assembler. Maybe u-boot gets
overwritten, but the blr isn't even reached if I change early_init by
just returning 0U immediately. Hmm.

Any pointers to help debugging would be really appreciated ;-)

Cheers,
Cajus