xinput ids

[Kai Hendry]

On Tue, 9 Jun 2015, at 01:23 PM, Peter Korsgaard wrote:
> In the likely situation that the touchscreens are of the same type they
> will have the same device name, so you need to fish out the
> corresponding /dev/input/event* device node and pass it to udevadm info
> (assuming that the server is local) to E.G. key off the ID_PATH
> (E.G. the USB port the touchscreen is connected to).

Yes, Mr Hutterer's "some device name" suggestion doesn't work since IIUC
my user's device comes up twice:

"""
Also using xinput with device name method wouldn't work either because
there are 2 same eGalax touchscreen devices listed from xinput, so it
couldn't tell which one to use, the only unique identification between
the
two is the device ID."""

Sorry, I still don't quite understand how to map /dev/input/event* via
udevadm. Do you have a worked example, perhaps with systemd I could peer
at?
http://s.natalian.org/2015-06-11/lsusb.txt

Many thanks from Cornwall,