I'm working with a custom made image of Slackware ARM 14.1 with kernel 3.8.X since about 3 years and now needed to upgrade kernel for cdc-acm driver and watchdog.
I've tried different kernels from distro supplied with BeagleBone (Debian 7.11 to 9.5, kernel 4.1.X to 4.14.X). Each time I replace files in /boot/ and /lib/modules and /lib/firmware, they are all booting properly but never been able to make UART working again.
With kernel 3.8.X, I was using /boot/uEnv.txt line :
I know there was changes between 4.1.X and 4.4.X and 4.14.X but tried each configurations with no success. Is it possible the issue is because I have a FAT partition for /boot/ and EXT4 partition for / ? Because I'll have to remote update systems so will not be able to change partitions.
Also could it be possible that the issue is the U-Boot version? From the debug serial :
U-Boot 2014.04-rc2-00015-g99288ca (Mar 12 2014 - 09:49:41)
Updated the U-Boot, still the same issue
U-Boot 2018.09-00002-g0b54a51eee (Sep 10 2018 - 19:41:39 -0500), Build: jenkins-github_Bootloader-Builder-65