After playing with the HID interface in OS X, I have found out there exists an API for simulating input events from user space, so I've implemented the touchscreen driver using it.
One unexpected caveat was that you need to set up an increasing event number to be able to click the menu bar. Even worse, when launched from XCode, the app would hang if you clicked the XCode menu bar. If you click any other app or launch it outside XCode, everything's fine. Caused some pain while debugging.
Now I still want to implement the driver as a kernel module. On the other hand, the userspace version is also fine. I want to add the support for multitouch gestures, though I'm not sure it is possible to provide multiple pointers to applications.
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The code is at github https://github.com/astarasikov/osxhidtouch
You can get the binary OSX touchscreen driver for the Dell S2340T screen from the link below. Basically, you can replace the HidTouch binary with your own, and if you put it to "HidTouch.app/Contents/MacOS/HidTouch", you will get an app bundle that can be installed to Applications and added to the auto-start.