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

Question

I am building a Yocto image for Intel Edison.

One of the image's components is u-boot with an Edison-specific patch. By default, Edison's UART port is used for u-boot console. I want to disable this feature, but only on the serial interface(u-boot also listens on USB and that needs to stay).

My main concern is the "Press any key to stop autoboot" feature on the UART port. I need this port to connect an accessory that might send something during the boot process of the main device.

How do I approach this problem? Is there an environment variable for this, or do I need to modify the sources?

Thanks in advance!

Solution 1

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;
     }
  

Example: If you are looking for board_early_init_f of Orange Pi 4B it is in /build/cache/sources/u-boot/v2020.10/board/rockchip/evb_rk3399/evb-rk3399.c

That's it. Hope this helps someone else!

---

see also

Solution 2

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. About U-Boot Environment Variables

Solution 3

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

Solution 4

As told by Kyle you can set the bootdelay u-boot environment variable to -2. This can even be done from a booted system using the fw_setenv utility. On my mender raspberry pi image this utility was preinstalled.

Using sudo fw_printenv bootdelay showed it was set to 2, i set it to -2 with sudo fw_setenv bootdelay -- -2 (note the -- before the value, so -2 is interpreted as the value, not an option).

In my case it was a similar issue than the OP, with a LoraWAN node on a raspberry pi connected over the serial port that interrupted the boot.

So

• remove the serial device causing issue
• set bootdelay either from the booted system or from the bootloader
• shutdown and add the serial device back

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Comments

[Egor]

Thanks for the feedback! I've seen the docs on the silent mode, but this method has one flaw - while the console's output is now turned off, the console's input(Press any key to stop autoboot) actually works and you can stop the device from booting. I need to set the UART port free to use it with an accessory. I'll update my question to address this issue