I just create an argv of all the environment variables of the firmware
and I pass the psysical address of that NULL terminated argv array
to the kernel command line like so... "u-boot-env=0x0f000f00".

This would be a variation of the "human readable ASCII format"
technique, right?  I had once ventured to offer my opinion that this
would be a technique that could work for all architectures, which is
a big plus, IMO.   My mistake was suggesting XML, which I think
was [mis]understood by some as requiring a lot more than a few
extra "</" type characters.  I'm offering my opinion not as an expert
but as someone who not too long ago tried to puzzle through the
bootloader/kernel interface and found it unnecessarily obscure.  I
think an ASCIIZ string array of some sort would be immediately
obvious and thus highly maintainable by all.

Mark Chambers