How does Linux assign a tty name to a certain UART?

I am debugging a single board computer that uses a Yacto Linux. It has 5 UARTS. When the system boots, what determines a) if a given UART is active, and b) what Linux port name is assigned to a particular UART?

For example, after booting the Linux console is /dev/ttymxc3. I’d like to know which physical UART it is using.

Thanks for any pointers. It may be that I just do not know the correct search term to use.