've got a Pi3B+ here with a 10" touch display connected to it (HDMI+USB). Both together consume about 11W, so I'd like to switch off the display whenever not needed. Probably will wake it up with a proximity sensor or a button or something, as soon as this is working.
I found some commands for switching off the display:
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"tvcontrol -o" switches off the display and the power consumption drops to ~5W. Unfortunately only for a couple of seconds. Then the display comes back up with a "No signal" message. Again with full 11W.
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"xset dpms force off" blanks the screen, but doesn't switch off the display.
Since the display is fully powered via an USB port of the Pi, I thought about just disabling the port. Unfortunately this doesn't seem to be so easy with newer kernels. One can only "request" for the power to be switched off. I tried "powertop" with no success, and also "uhubctl -l 1-1.1 -a 0", which says that it switched off the port, but nothing happens.
So I assume that the request for switching the power off is denied, since there is an actual device (the touch screen of the display) connected. Am I right? Then how do I disable that first and enable it again on wakeup?