I have a HP 2310ti 23" touch screen display, that's connected to USB. It's identified as the following:
ID 0408:3001 Quanta Computer, Inc. Optical Touch Screen
Since upgrading from Ubuntu 14 to 16.04 LTS (and from 3.x kernel to 4.x), the touch screen stops responding whenever the screen goes into standby. I have no screen saver as such, the screen just fades to black and the monitor goes into standby mode after a few minutes.
The computer has no keyboard or mouse attached, so there's no way to wake up the display, except remotely over VNC. If the screen is woken up over VNC, the touch screen works again like normal.
Having had the display for a long time, I know from experience that the touch screen is a separate device from the display. The touch screen normally registers touches even if the display isn't turned on from the power switch.
What I've tried so far:
Suspecting the problem might be a new USB power saving thing in the 4.x kernel, I tried to find solutions related to that.
The /sys/bus/usb/devices/usb2/2-1/2-1.4/power/control is set as "on" by default, and I tried setting the power/autosuspend to "-1", but there was no change.
What should I try next? Is there somewhere in particular I should look for somekind of debugging info, so I could see what happens when the screen goes into standby?