@ixi
The latest firmware is required in order to boot on the 7900 series cards. There are some other issues with mesa that causes flickering and losing the cursor. One can get around that with some work and some knowledge & skills. I created a test ISO that works. But there are a number of things you would need to do after to overcome the flickering and cursor issues. It’s not just a matter of the 6.1 kernel. The card works on Windows. If you pm me i can provide you more information if you like.
Edit: Here is the post from another user that has it working