Plan 9 from Bell Labs kernel images require additional setup to pass
  configuration information to the kernel.  An environment variable named
  confaddr must be defined with the same value as CONFADDR (see mem.h).
  Use of this facility is optional, but should be preferable to manual
  configuration.
  
  When booting an image, arguments supplied to the bootm command will be
  copied to CONFADDR.  If no arguments are specified, the contents of the
  bootargs environment variable will be copied.
  
  If no command line arguments or bootargs are defined, CONFADDR is left
  uninitialized to permit manual configuration.  For example, PC-style
  configuration could be simulated by issuing a fatload in bootcmd:
  
    # setenv bootcmd fatload mmc 0 $confaddr plan9.ini; ...; bootm
  
  Steven Stallion
  June 2013