How can use earlycon in the agx xavier

Robotics & Edge Computing Jetson & Embedded Systems Jetson AGX Xavier
6

It seems you are using the custom carrier board.

I would suggest you could ask your vendor for the debug UART port.

For AGX Xavier devkit, customer could use Micro-USB port for debug UART as following:
NVIDIA Jetson Xavier - Serial Console (ridgerun.com)