Gadget Implementations - notro/gud GitHub Wiki
GUD Gadget open source implementations.
Linux
Source: https://github.com/notro/gud/tree/master/buildroot/external/linux-patches/gud_gadget
Wiki: https://github.com/notro/gud/wiki/Linux-Gadget-Driver
Userspace Linux
It should be possible to implement GUD in userspace using USB FunctionFS. The problem is that AFAICT this leads to a memcpy when the USB buffer crosses from the kernel into userspace. This will degrade performance, but since I haven't tried it I don't know how severe that is.
Going from userspace into the DRM buffers is no problem since they can be mmap'ed.
Rust implementation (WIP): https://github.com/samcday/gud-gadget/
Raspberry Pi Pico
Source: https://github.com/notro/gud-pico
ESP32
https://github.com/affbotics/esp32-usb-monitor
Android
It would have been really cool to see old tablets and phones reused as GUD touch displays!