I actually enjoy your video @ youtube a lot. Thank you first.
According my current 5.6 kernel: Yes, the GPU clockrate is required to imposed. Or it will get really unstable if you enable panfrost.
If you have a newer kernel, you might try it without setting clockrate first. If thing went bad for you, just remember to try this.
I use the kernel ripped from libreELEC at https://gitlab.com/FuyuriSeiji/linux-5.6-le
I made changes into build system config to use this kernel
For the root, I use Gentoo's and emerge mesa with VIDEO_CARDS="panfrost."
And the patched of ffmpeg at https://gitlab.com/FuyuriSeiji/ffmpeg
These enable my setup to have hardware decoding with DRMPRIME kodi.
If you have ever bumped any problem, you might consider what I list here as alternative approach.
Good luck