How to disable serial console(non-kernel) in u-boot

I'm getting back to this issue almost a year later, now I've managed to find a proper solution.

The board I was working on had a reasonably new u-boot in its BSP. To disable the serial console I had to do the following:

• Add the following defines to the board's config header(located in include/configs/board.h):

  #define CONFIG_DISABLE_CONSOLE
  #define CONFIG_SILENT_CONSOLE
  #define CONFIG_SYS_DEVICE_NULLDEV
  

• Check if your board has early_init_f enabled in the same file:

  #define CONFIG_BOARD_EARLY_INIT_F 1
  

• Find the arch file(Something like arch/x86/cpu/architecture/architecture.c) and add this call to its early_init_f function. It actually modifies board's global data variable to have these flags:

  gd->flags |= (GD_FLG_SILENT | GD_FLG_DISABLE_CONSOLE);
  

• My board did not have one, so I had to add the whole function

   int board_early_init_f(void)
   {
        gd->flags |= (GD_FLG_SILENT | GD_FLG_DISABLE_CONSOLE);
        return 0;
   }
  

That's it. Hope this helps someone else!

There's no way to do this, without modifying the source (configuration) of U-Boot.

To disable the serial console in U-Boot, you need to reconfigure U-Boot. The documentation from the master branch of U-Boot: Readme.silent

According to that one, you need to set:

CONFIG_SILENT_CONSOLE
CONFIG_SILENT_CONSOLE_UPDATE_ON_SET
CONFIG_SYS_DEVICE_NULLDEV

CONFIG_SILENT_U_BOOT_ONLY is also needed if you want only U-Boot to be silent.

You might also need to test with CONFIG_SILENT_CONSOLE_UPDATE_ON_RELOC and possibly adding silent 1 to CONFIG_EXTRA_ENV_SETTINGS.

== UPDATE ==

See the following options for a possible workaround:

CONFIG_ZERO_BOOTDELAY_CHECK
CONFIG_AUTOBOOT_KEYED
CONFIG_AUTOBOOT_KEYED_CTRLC
CONFIG_AUTOBOOT_PROMPT
CONFIG_AUTOBOOT_DELAY_STR
CONFIG_AUTOBOOT_STOP_STR

These options will at least give you a way of requiring a magic string to stop the boot. It might be enough to help you. See README.autoboot

Setting the u-boot environment variable bootdelay to -2 disables the ability for the UART to interrupt the boot process on U-Boot 2017.01 release. It appears that -1 is a special case.

See common/autoboot.c from your U-Boot source tree for details.