How to Disable Serial Console(Non-Kernel) in U-Boot

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;
     }
  

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!

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see also

Why doesn't U-Boot disable the console output

U-Boot is doing exactly what it should (silencing the output) with the following command:

#define CONFIG_EXTRA_ENV_SETTINGS \

        "silent=1\0" \

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see also

How do I turn off the console on an embedded system built with Yocto?

For kernel versions 5.11 and newer:

In the submenu "Character devices" under "Device Drivers" from make menuconfig, there is an option called "Null TTY driver" (CONFIG_NULL_TTY) that you can enable and add console=ttynull to the kernel boot cmdline so that all console output will be simply discarded.

You can also disable CONFIG_VT and CONFIG_UNIX98_PTYS, since you don't need to interact with your program via console at all.

For older kernels (like my 4.14):
You can add this support with the diffs at: https://lore.kernel.org/lkml/20190403131213.GA4246@kroah.com/T/ and then follow the instructions above.

Kernel no serial console output if started through U-Boot

After some time with other tasks at hand I revisited the problem and literally magically found a working config. I still don't understand how the same kernel command line worked coming from cmdline.txt but not from u-boot's bootargs. Until further proof I'll assume gross negligence on my side. ^^

So now I'll post my boot.cmd for our cm3 and 3B+ in hopes it helps others.

cm3

setenv fdtfile bcm2710-rpi-cm3.dtb

mmc dev 0
fatload mmc 0:1 ${kernel_addr_r} Image
fatload mmc 0:1 ${fdt_addr} ${fdtfile}
setenv bootargs console=ttyAMA0,115200 printk.devkmsg=on usbcore.autosuspend=-1 fsck.mode=force fsck.repair=yes
booti ${kernel_addr_r} - ${fdt_addr}

3B+

setenv fdtfile bcm2710-rpi-3-b.dtb

fatload mmc 0:1 ${kernel_addr_r} Image
fatload mmc 0:1 ${fdt_addr} ${fdtfile}
setenv bootargs 8250.nr_uarts=1 console=ttyS0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 rootwait
booti ${kernel_addr_r} - ${fdt_addr}

Disclaimer: This is a rough cut. But as I fell into despair making this work I wanna get this solution out as fast as possible

Having trouble stopping U-Boot autoboot

So it turns out there is a short somewhere between the RX pin and the +3.3V pin which is not allowing me to send anything to the board. Thank you to those who have commented.

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