I finally came across this thread here,
Seems to be the same problem I'm having.
I am having serious problems with the touchscreen on my 4.3" display. I actually have two sets of Overo Waters + Chestnut43s and the problem is the same.
I set the environment correct, and occasionally the ts_calibrate program runs at boot. I can usually get 1 touch event before it stops working completely. Occasionally after trying holding the screen in many different positions and pressing with varied pressure, it registers a couple more touch events. After awhile, it seems like I can get through the calibration, but the touchscreen continues to be unresponsive
The problem is consistent on 2 entirely different sets of hardware.
I've tried updating to the latest dev build of u-boot, and openembedded with no luck. I've tried modprobe -r ads7846 && modprobe ads7846, etc... Am I missing something or did I get a bad set of touchscreens?