Virtual displays for Sunshine/Moonlight without dongle on amdgpu in Bazzite-Gnome

Introduction

Users of GPUs leveraging the amdgpu driver can create virtual displays without using any dongle for use with Sunshine. This can be done via a kernel parameter as described here and here. However we opt for bringing up the screen during multiuser-target. This has the advantage of a faster boottime and it keeps the splash screen intact.

Preparation

Install Sunshine

To install Sunshine open a terminal and enter:

ujust setup-sunshine

Identify ports

You need to identify actual ports on your GPU to map the virtual display to. The following command will list potential ports (DP-1 - DP-X, HDMI-1 - HDMI-X).

for p in /sys/class/drm/*/status; do con=${p%/status}; echo -n "${con#*/card?-}: "; cat $p; done

Any disconnected port will do.

Prepare EDID firmware to accomodate your target screen

To make the kernel aware of the proper resolution and refresh rate of your virtual display we need an EDID firmware file. This can either be retrieved for example here [1]. Alternatively you can also create a tailored EDID file with this handy tool [2]. The tool takes a modeline from xorg and generates the EDID bin from it. To get a modeline for your target resolution you can use this website [3]. To prepare and use edid-generator on Bazzite-Gnome proceed as follows in a terminal:

ujust distrobox-assemble //Choose Ubuntu
distrobox enter ubuntu
sudo apt install zsh edid-decode automake dos2unix
mkdir -p ~/build/
cd ~/build/
git clone https://github.com/akatrevorjay/edid-generator
cd edid-generator
./modeline2edid - <<< 'Modeline "2560x1600" 348.16 2560 2752 3032 3504 1600 1601 1604 1656 -HSync +Vsync' //Replace with your modeline in the single brackets
make

You should now have a .bin file named according to the content of the first brackets in the modline. Copy this into your local firmware folder. Carry on in the terminal:

mkdir -p /usr/local/lib/firmware
sudo cp 2560x1600.bin /usr/local/lib/firmware/

Test your target display

We will now create a helper script to enable your virtual display.

Open the editor of your choice and paste the following, then replace DP-2 with a non connected interface and 2560x1600.bin with your EDID file:

#!/bin/bash
cat /usr/local/lib/firmware/2560x1600.bin > /sys/kernel/debug/dri/0/DP-2/edid_override
echo on > /sys/kernel/debug/dri/0/DP-2/force
echo 1 > /sys/kernel/debug/dri/0/DP-2/trigger_hotplug

Save the file as "enable-screens.sh". Then make it available to the root user:

sudo cp enable-screens.sh /usr/local/sbin/
sudo chmod +x /usr/local/sbin/enable-screens.sh

You can now test if everything works:

sudo /usr/local/sbin/enable-screens.sh
gnome-control-center display

The control center should now start up with the display section and show the newly created display.

Automation

Automatically bring up screen via systemd

You can trigger the script on startup via a systemd unit file. For this open the editor of your choice and paste the following:

[Unit]
Description=Enable Virtual Displays

[Service]
ExecStart=/usr/bin/bash /usr/local/sbin/enable-screens.sh

[Install]
WantedBy=multi-user.target

Save under "/etc/systemd/system/enable-screens.service". Then enable the service and reboot:

sudo systemctl daemon-reload
sudo systemctl enable enable-screens.service
systemctl reboot

After the system has restarted check your display is available in control center:

gnome-control-center display

Autostarting Sunshine

Sunshine autostart is currently not working in bazzite-gnome [4]. To work around this use xdg autostart.

sudo cp /usr/share/applications/sunshine.desktop /etc/xdg/autostart/

Switching screens in Sunshine

Gnome has recently added gdctl as a tool to manipulate screen layout across X and Wayland. This can be used in a Sunlight application in "Do Command" and "Undo Command" to setup the appropriate screen configuration. I use this to enable a multiscreen setup in desktop mode, but I also have an exclusive desktop mode just on my tablet and exclusive Big Picture to my tablet.

For the multiscreen "Do Command" add (I use scale on the small tablet screen to get a readable UI):

gdctl set --logical-monitor --primary --monitor DP-1 --logical-monitor --monitor DP-2 --scale 2 --right-of DP-1

In "Undo Command":

gdctl set --logical-monitor --primary --monitor DP-1

You can now connect to the application from your device with Moonlight.

Conclusion

I hope this little guide was helpful. Please put pointers to problems and I will try to correct them in the original post. Feel free to also share your successes. Enjoy your virtual display and Sunshine/Moonlight.