CONFIG_AT91_DEBUG_LL_DBGU3 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_AT91_DEBUG_LL_DBGU3.
Result is shown for kernelversion 5.19-rc1

Kernel low-level debugging on sama5d2

configname: CONFIG_AT91_DEBUG_LL_DBGU3

Kernel low-level debugging port
└─>Kernel low-level debugging on sama5d2
In linux kernel since version 4.3 (release Date: 2015-11-01)