T20 Hang on Boot

Kernel hang up when modified u-boot variable from console=ttyS0 to console=null.
The issue occurs on multiple reboots.
I have attached the log from LCD Display,

hello Ashokkumar

Welcome to the Toradex Community.
Could you please send a dmesg log, since the images are not clear? Were there any issues during the installation of Bsp 2.8b2? Which LCD Display are you using?

hi jaski,

Sorry for images, but i could only get those images since system hang up. System is not booting after hang up, i have no access to prompt. No issue during installation. I am using EDT 7 inch Display.

You should connect the board over UART_A (standard console port) to the Host and then turn the module on. For copying the text from console you can follow the instructions on this site.

This issue has occurred after disabling the UART console only.

Sorry, I missed that.

If you disable the console, you should still see the uboot, then you can stop the boot process by pressing any key. Once you are u-boot, you can reset the u-boot variables.

  1. env default -a
  2. saveenv

Additionally you can put the module in recovery mode and flash the module again.

This issue occurs only when disabling serial console, since i used serial port for other purpose need to disable console. Is there any fix or workaround for the issue.

I have tested disabling the console with Bsp Colibri-T20_LXDE-Image 2.8b2.97 20180331 and I have no kernel hangs.
Did you connect anything to console serial port? Are you sending receiving data on serial console port during the startup of linux?

yes, waiting for data in serial port.

how do you make the module wait for receiving data on startup? Is this during the uboot? Did you set also a timeout to continue with the uboot if the data is not arrived on given time?

After boot module will wait for data in serial port.

ok, will the module wait for infinite time?

Actually my code will run by systemd after sytem is booted up the hang happens before mounting rootfs itself.

As @jaski.tx mentioned, it seems to work here with 2.8b2. So, when you disconnect what is connected on UART_A, does it work for you? I would first try without an external device connected, just to make sure that it does not interfere in any way…

Issue occurance not consistant, simulated using continuous reboot test.

so you mean, the issue is still there, when nothing is connected to UART. How many errors during how many test do you have?