Default [Q] Serial Console on Xperia devices?

Hi, is there any information on how to connect to the serial console on Xperia devices?
I looked into the sources of an Xperia Z1 Compact and found that
activates the serial console (see arch/arm/mach-msm/board-8974-console.c).
Has anybody tried a magic USB micro cable with different resistor values like for the Samsung i9100?

A console will help me debug kexec to jumpstart custom firmware on those devices with a locked bootloader.