First many thanks for your reply.
I can understand resource problems you mentioned.
That's why I tried to help me alone during several days as a lot of people do. My initial problem was accelerated video. A little bit later I discovered BT issue. I was thinking BT will be easier to solve but hard enough for low experienced ARM people like me.
I'm software developer and I tried to build Mali driver from official open sources with recent kernel found in Armbian.
I quickly understand that Mali sources are not ready for such recent kernel. A lot of kernel refactoring like: timespec, Y2K38 bug, and more cause Mali sources unable to build. I fixed some Mali code to progress but I need to fix more stuff to obtain a mali.ko fully functional.
ARM world is a new world for me: I have a lot to understand to progress. DTB and so on...
If you have any recommendations (tuto, docs, ...) to help to progress as quick as possible, don't hesitate to give me some URLs