> It would be nice :). In its absence, xf86-video-modesetting should be
> used. But without firmware you don't have KMS, so ... 

Done.

> What kernel version is used?

4.20.4-gnu

> What does dmesg say about amdgpu?

Absolutely nothing.

> Anyway i'm suspect that without a firmware (deblobed in linux-libre) KMS
> and power management (and hibernation too) will not work.

Any idea where I could get more info about that?

Also what good it the amdgpu without the firmware?  What's the role of the
firmware in the picture?

-- 
Pierre Neidhardt
https://ambrevar.xyz/