The am335x touchscreen driver in processor sdk 02.00.01.07 sometimes gives bad coordinates on pen-up. Most of the time this is filtered out by the tslib modules variance and dejitter.
Examine on am335x-evm hardware. edit /etc/ts.conf and comment out the lines for variance and dejitter filtering. run ts_test. Put ts_test in draw mode. Touch screen (pen-down, pen-up) many times on right hand side of screen. Observe occasional line draws to far right of screen. Example attached below.
I was able to fix this by bringing in the fifo interrupt handling code from the old kernel 3.2 driver and adjusting for the newer driver in the above mentioned sdk based on kernel 4.1.13. Its seems the fifo somehow has bad values in it possibly as part of sampling at the pen-up interrupt? I instrumented the driver to printk the raw fifo values. The old driver was filtering "out of range" values. The new driver sorts, discards high and low values, then averages.
