RPI 4 with DSI 7'' Touchscreen: sleep does not work (XSET)

[AGTDesigns]

Hi,

I hope I don't mess up on the bug report, but here it goes.

I've encountered an issue with RPi4 and Official 7'' Raspberry touchscreen connected by DSI.

The software is the latest Raspbian, and I've made also an apt-upgrade.

The following instructions are in start-up script, which worked flawlessly on a RPi3 with the same display:

#!/bin/bash
export DISPLAY=:0
xset s 10

On the Pi3, after 10 seconds of inactivity the backlight turned off, and the screen went black. If the mouse was moved/screen touched/key pressed the screen would turn back on.

On the Pi4, the screen goes black, the backlight keeps on, and it does not awake back when I move the mouse / press any key.

Is there any specific additional information I can provide to help solve this issue?

If I comment the xset command and let the pi run for a while, the screen eventually goes off, but the backlight keeps on. Nevertheless, it comes back after moving the mouse/touching the display.

I wanted to upgrade an wall-mount screen for Home Automation (Home Assistant) to the faster RPi4, and being able to have the screen off most of the time is very handy to lower power consumption, heat and also unnecessary night light.

Thanks!

[JamesH65]

There is a change in rpi-update that will hopefully fix this.
raspberrypi/linux#3289