default or selected kernelversion does not have config value CONFIG_SERIAL_S3C6400.
Result is shown for kernelversion 6.2.5

Samsung S3C6400/S3C6410/S5P6440/S5P6450/S5PC100 Serial port support

modulename: s3c6400.ko

configname: CONFIG_SERIAL_S3C6400

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>Samsung S3C6400/S3C6410/S5P6440/S5P6450/S5PC100 Serial port support
In linux kernel since version 2.6.29 (release Date: 2009-03-23)  
Serial port support for the Samsung S3C6400, S3C6410, S5P6440, S5P6450
and S5PC100 SoCs

source code:
drivers/tty/serial/s3c6400.c