Dual displays not working using v2.87.16+rev1 or newer

I tried searching around but could not find anyone else with the same issue I am experiencing. I apologize if this is a duplicate post or if I am missing reading some documentation.

I am having troubles with v2.87.16+rev1 or newer and dual displays. I am running a container with xorg on a Raspberry Pi 4B 4GB with an official 7 inch raspberry pi touchscreen and 4K HDMI monitor and can only get one monitor to display even when BALENA_HOST_CONFIG_max_framebuffers=2 is set. The same code runs fine on v2.85.2+rev3 and lower (only tested up from v2.73.1+rev1). I would like to stay current with the recommended version so I thought I would ask if anyone else is having this issue. I put together a sample code base to replicate the problem here: Kevin Minshull / Balena DM · GitLab

Hi Kevin, off the top of my head it seems like this might be related to a power consumption issue with the screens. However, the fact that it works with a previous OS is odd. Just to rule out whether power consumption is an issue, could you try using different screens to see if it persists?

I was able to try this on different displays. An old 720p and a new 4K and have the same behavior.

hello @TheUnexplained

Thanks for providing the detailed context.

Are you still running into this issue?

Can you please confirm the following

  • Do you have any dtoverlay values set on the device? can you provide the ouput of cat /mnt/boot/config.txt by running the command by ssh’ing into the hostOS?
    if you have vc4-kms-v3d set, can you please try by setting BALENA_HOST_CONFIG_dtoverlay=vc4-fkms-v3d in Device configuration?
  • You mentioned that only one display works, is it always the first display?