RPI4 Dual Monitor blanking

grantc66

Started a new project with a dual monitor setup using a pi4. Connected via DVI as there is no HDMI (only display port, thanks HP).

Monitors are in portrait mode & MM is setup in single instance configuration using this post as a template (linky)

The latest version of Bullseye seems to have stopped “vcgencmd display_power 0” from working , it no longer blanks the display and just responds with display_power=1. This appears to be due to a change to the KMS driver.

Googling give me this as an alternative

xrandr --output HDMI-1 --off

It does work & switches the screens off (separate commands for HDMI-1 & HDMI-2) however, using

xrandr --output HDMI-2 --off
xrandr --output HDMI-1 --off

to switch off and

xrandr --output HDMI-1 --rotate right --auto
xrandr --output HDMI-2 --rotate left --right-of HDMI-1 --auto

Puts them back in the right place . Sometimes.
About 1 in every 10 off/on cycles the righthand display ends up on HDMI-1 & HDMI-2 shows the desktop. CTRL W puts it back in the right place, but that’s really annoying & I don’t want to reset the MM every time as it looks ugly whilst repopulating.

Has anyone found a more reliable method to blank the displays & return MM back to the correct displays?

wishmaster270

@grantc66 Hi,

it may be a timing issue.
Maybe a sleep 1 between the two xrand commands helps.

grantc66

@wishmaster270 Thanks for the suggestion. Unfortunately not a timing issue.

Adding a delay didn’t change the behaviour. ☹️

grantc66

After nearly a week of trying different things, short of removing the KMS driver or reverting to Buster, the only method I could come up with was to use the xset screensaver.

Set the timeout to 3 minutes
xset -display :0 s 180
and do
xset -display :0 s reset
to wake it up on motion.

It’s not elegant but without any cec control of the monitor it appears to be my only solution, unless anyone has a method to get xrandr to keep electron on the correct monitor.

wishmaster270

@grantc66
There are ways to move windows to a specific screen on the bash. But it is complicated.
Maybe one of the solutions in this thread solves your problem.

grantc66

@grantc66

For anyone having the same issue:

Another solution is to edit /boot/config.txt & change to the fake kms driver

dtoverlay=vc4-kms-v3d

to

dtoverlay=vc4-fkms-v3d

reboot & then

vcgencmd display_power 0
vcgencmd display_power 1

work as they used to do.

I’ve not noticed any negative effect from using the fake one but I’m not using any 3D effects (your results may vary).

grantc66

For anyone having this issue:

Change the kms driver to the fake one by editing /boot/config.txt

change

dtoverlay=vc4-kms-v3d

to

dtoverlay=vc4-fkms-v3d

Reboot & display will now switch on/off using

vcgencmd display_power 0
vcgencmd display_power 1

I’ve not noticed any problems using the fake driver but I’m not using anything 3D (your results may be different)