The following two patches add three commands to xmon for stopping,
restarting and dumping info about spus from xmon.
For the folks on linuxppc-dev, these patches depend on another patch
which isn't in the powerpc tree yet AFAIK, you can get it here:
http://kernel.org/pub/linux/kernel/people/arnd/patches/2.6.17-arnd8/broken-out/spu-add-attributes.diff
cheers