This is a somewhat naive binary that exists primarily to test/demonstrate the gud-gadget implementation.
It takes full control of a drm card and writes framebuffer data there.
Chances are your host machine (presumably a desktop/laptop PC) is more powerful than the postmarketOS device you're testing with.
You can build this crate for pmOS targets using cross:
# Run these commands from the top level gud-gadget directory.
# For arm64 devices
cross build --release --target aarch64-unknown-linux-musl
# For armv7 devices (untested)
cross build --release --target armv7-unknown-linux-musleabihf
You can then copy the statically linked binary from ./target/aarch64-unknown-linux-musl/release/gud-gadget-drm to the target device.
Running it from the device is simple:
# Stop the graphical desktop.
service tinydm stop
# Run the gadget
./gud-gadget-drm /dev/dri/card0 # or whichever card is available on your device