Raspberry Pi serial console question

Hi, all,

I want to use a Raspberry Pi 3's main serial port, which by default 
mirrors the console, even when "console=fb" is used.

I've forgotten how to disable serial console on this port so that kernel 
messages don't get sent to the machine to which this serial port is 
connected, and search engines suck these days.

Does someone remember how to do this?

Thanks,
John