The config option CONFIG_SILENT_CONSOLE can be used to quiet messages
  on the console.  If the option has been enabled, the output can be

  silenced by setting the environment variable "silent".
  
  - CONFIG_SILENT_CONSOLE_UPDATE_ON_SET
  	When the "silent" variable is changed with env set, the change
  	will take effect immediately.
  
  - CONFIG_SILENT_CONSOLE_UPDATE_ON_RELOC
  	Some environments are not available until relocation (e.g. NAND)
  	so this will make the value in the flash env take effect at
  	relocation.

  
  The following actions are taken if "silent" is set at boot time:
  
   - Until the console devices have been initialized, output has to be
     suppressed by testing for the flag "GD_FLG_SILENT" in "gd->flags".

  
   - When the console devices have been initialized, "stdout" and
     "stderr" are set to "nulldev", so subsequent messages are
     suppressed automatically. Make sure to enable "nulldev" by

     #defining CONFIG_SYS_DEVICE_NULLDEV in your board config file.

  
   - When booting a linux kernel, the "bootargs" are fixed up so that
     the argument "console=" will be in the command line, no matter how

     it was set in "bootargs" before. If you don't want the linux command
     line to be affected, define CONFIG_SILENT_U_BOOT_ONLY in your board
     config file as well, and this part of the feature will be disabled.