Enable framebuffer console in Android kernel source Is it possible to somehow enable the framebuffer console in android kernel sources from samsung, to see kernel messages instead of just the bootlogo?
You didn't really say what you were trying to do exactly-- but if I understand right, and you're any good with soldering, it sounds like you might want to find the UART pins on your device, then tap that and use a serial connection to your computer to read the bootloader output (via minicom or some other terminal emulator) and access the live console that way.  You may also be able to get serial data from the USB during boot.

Of course, if you are just stuck with a non-booting system and trying to recover a device, you might use odin/heimdall to reflash your boot image (including a new kernel) or install a custom recovery image and use that to flash a ROM with a good kernel.

It sounds like you're possibly deliberately messing with your own built kernels- maybe to upgrade to a new kernel base or something?  If that's the case, an alternative to seeing the kernel messages onscreen is to enable PSTORE (the file system-based replacement for /proc/last_kmesg), which will let you view the dmesg/kernel console + any panic messages after a bad boot on the next reboot (so long as the ram doesn't get overwritten).  Take a look at this example from the trlte (Samsung Note 4) kernel for how to implement it in the newer kernels.  (If it's an older kernel you may just need to turn on last_kmesg.)