Early console using ARM semihosting

modulename: earlycon-arm-semihost.ko

configname: CONFIG_SERIAL_EARLYCON_ARM_SEMIHOST

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>Early console using ARM semihosting
In linux kernel since version 3.16 (release Date: 2014-08-03)  
Support for early debug console using ARM semihosting. This enables
the console before standard serial driver is probed. This is enabled
with "earlycon=smh" on the kernel command line. The console is
enabled when early_param is processed.

source code: