Tried this command on my local device with all the above points mentioned.
sudo udevadm test /devices/platform/bus@0/3100000.serial/tty/ttyTHS1
snippet:
Reading rules file: /etc/udev/rules.d/99-tegra-devices.rules
Reading rules file: /etc/udev/rules.d/99-tegra-mmc-ra.rules
Reading rules file: /etc/udev/rules.d/99-tty-ths0.rules
value '[dmi/id]sys_vendor' is 'NVIDIA'
value '[dmi/id]sys_vendor' is 'NVIDIA'
ttyTHS1: /usr/lib/udev/rules.d/50-udev-default.rules:25 GROUP 20
ttyTHS1: /etc/udev/rules.d/99-tty-ths0.rules:2 LINK 'mys'
ttyTHS1: Preserve permissions of /dev/ttyTHS1, uid=0, gid=20, mode=0660
ttyTHS1: Handling device node '/dev/ttyTHS1', devnum=c240:1
ttyTHS1: sd-device: Created db file '/run/udev/data/c240:1' for '/devices/platform/bus@0/3100000.serial/tty/ttyTHS1'
DEVPATH=/devices/platform/bus@0/3100000.serial/tty/ttyTHS1
DEVNAME=/dev/ttyTHS1
And it will create the symlink.
nvidia@tegra-ubuntu:/dev$ ll mys
lrwxrwxrwx 1 root root 7 Sep 23 06:45 mys -> ttyTHS1