Where I can find the source?
As far as I searched what is free software is the Vulkan implementation that runs on top of the intrinsic GPU and drivers (that have DRM and no source code).
The intrinsic GPU drivers on the kernel are still close source. So basically AMD and NVIDIA are the same. They both have source for some engines implementation but both kernel drivers are close source.
https://github.com/GPUOpen-Drivers/
amdgpu is a blob.
I'm missing something?