OFW access from linux

Paul Fox pgf at laptop.org
Tue Sep 15 10:42:46 EDT 2009

on the XO, openfirmware stays resident when linux runs, and is
accessible via an API specified in arch/x86/kernel/ofw.c.  i've
just pushed a commit to our 2.6.30 kernel branch that adds a
sysrq hook (SysRq-y) for starting (returning to?) the resident
OFW command line interface.  when invoked, you can do all the
usual OFW peeking and poking, and even play pong.  (and, since
linux is still active, you can royally trash your system if
you're not careful.)

there's no SysRq key on the XO keyboard, so you'll need to use a
break on the serial console to invoke it, or, usually easier: 
"echo y > /proc/sysrq-trigger".  use "resume" from OFW to let
linux run again.

OFW itself prevents invocation on secure machines, so this
only works when unlocked.

 paul fox, pgf at laptop.org

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