System with serial console, which system is responsible for flow control settings

I have a proprietary Linux system, with a proprietary init system, which uses a serial console. I lately noticed, that the xon/xoff flow control is active on this serial console, which poses the risk of hanging the boot process when the xon character (0x13) is received by line noise. Looking at other systems with serial consoles (systemd based) shows that flow control is disabled there for the serial console, which seems sane. The question is, which part of the system is responsible for deactivating the flow control of the console tty? Is this done by the init process or the kernel itself? I.e., is this an error within the kernel configuration or must the init system be fixed to disable the flow control? I know, that the flow control can be disabled using the

()

function or by running

-ixon -F /dev/console

, but for a reliable system, this should be disabled before any process writes output to the console. I already browsed the systemd source code but wasn't able to find any code disabling flow control there.