meta-raspberrypi/recipes-core/udev/udev-rules-rpi/99-com.rules

KERNEL=="ttyAMA[01]", PROGRAM="/bin/sh -c '\
	ALIASES=/proc/device-tree/aliases; \
	if cmp -s $ALIASES/uart0 $ALIASES/serial0; then \
		echo 0;\
	elif cmp -s $ALIASES/uart0 $ALIASES/serial1; then \
		echo 1; \
	else \
		exit 1; \
	fi\
'", SYMLINK+="serial%c"

KERNEL=="ttyS0", PROGRAM="/bin/sh -c '\
	ALIASES=/proc/device-tree/aliases; \
	if cmp -s $ALIASES/uart1 $ALIASES/serial0; then \
		echo 0; \
	elif cmp -s $ALIASES/uart1 $ALIASES/serial1; then \
		echo 1; \
	else \
		exit 1; \
	fi \
'", SYMLINK+="serial%c"