CONFIG_DEBUG_AT91_SAMA5D4_USART3 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
Kernel low-level debugging on SAMA5D4 USART3
configname: CONFIG_DEBUG_AT91_SAMA5D4_USART3
Kernel low-level debugging port
└─>Kernel low-level debugging on SAMA5D4 USART3
In linux kernel since version 4.1 (release Date: 2015-06-21)
Say Y here if you want kernel low-level debugging support
on the USART3 port of sama5d4.
on the USART3 port of sama5d4.