Disable console output on Uart A

Technical Support
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1

Colibri Imx7 512MB V1.1D
Viola Rev 1.2
Linux BSP: 5.7.6 (dunfell)

I have read following post and build u-boot
serial/UART
I got null console, working as expected but when ever I am rebooting or shutdown system from keyboard/ssh I am getting following on UART A
command: reboot
Output: [ 41.521168] reboot: Restarting system
command: shutdown -h now
output: [ 24.857378] reboot: System halted

2

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To fully disable console output on UART A during reboot and shutdown on your Colibri iMX7 512MB V1.1D with Linux BSP 5.7.6 (dunfell), you can try the following steps:

  1. Kernel Boot Parameters: Modify the kernel boot parameters to suppress console messages. You can add console=null or quiet to the kernel command line. This can be done by editing the U-Boot environment variable bootargs. For example:

    setenv bootargs 'console=null'
saveenv

  2. U-Boot Configuration: Ensure that the U-Boot environment is correctly set to not pass any console parameters to the kernel. Double-check that there are no conflicting settings that might re-enable console output.

  3. Kernel Configuration: If the above steps do not resolve the issue, you may need to reconfigure the kernel to ensure that it does not output messages to the console during shutdown or reboot. This might involve recompiling the kernel with specific options disabled.

  4. Device Tree: Review the device tree configuration to ensure that UART A is not being used for console output. This might involve modifying the device tree source to disable the console on UART A.

By following these steps, you should be able to suppress the unwanted console output on UART A during system reboot and shutdown.

Please, also check if these links can help you solve your problem:

Disable serial console apalis imx6.

3

Hi @bharat_sabne,
Is this solved or still need assistance?

4

hi @sahil.tx
Not able to solve this issue, need assistance
I have done few changes in uboot after that I was able to disable almost everything on Uart A but still whenever I reboot or shutdown system I am getting message. One more observation while experimenting with back light I was getting error related to back light also [FAILED] Failed to start Backlight …re display brightness setting.
See ‘systemctl status backlight.service’ for details.
[ OK ] Started Update UTMP about System Runlevel Changes.

Attaching file with git diff for your reference
uboot-diff.txt (2.4 KB)

5

Hi @bharat_sabne,
I followed the steps mentioned here and was able to disable the console completely.

  1. Make the changes in both the files ( colibri_imx7_defconfig & colibri_imx7.h ) as mentioned in the article.
  2. Compile the u-boot and generate u-boot-nand.imx. For your ease of testing, I have compiled it, please download it from here
  3. Deploy the new u-boot
  4. Now, after reboot, make the below changes accordingly
To disable u-boot messages
`fw_setenv silent 1`
To disable kernel messages
`fw_setenv console null`
To disable serial getty
`systemctl mask serial-getty@ttymxc0.service`

This will completely disable your console, however, you will still be able to login via ssh

6

Hi Sahil,

I am getting results as expected