Hey anon, I'm desperately need to tell you something about the xf86-video-ati driver. Well apperently, just recently I made a switch to use a linux libre kernel and it seems to work flawlessly on most of its free driver modules that can be loaded at boot into xorg server without kernel mode drm. The xf86-video-ati source code can be reach at its github here
https://github.com/freedesktop/xorg-xf86-video-ati, there's also other alternative sources available which you can easily find it on the internet.
So, according to its shell man page documentation they provided, it only mention few option of modesettings modules that can be loaded into linux-libre kernel. The choices are "glamor", "exa" and "xaa" which being said that "xaa" it's an traditional technique of acceleration method according to
https://manpages.ubuntu.com/manpages/precise/man4/radeon.4.html. I read somewhere about the glamor modules, supposely it is the highest end of xf86-video-ati module has to offer. Out of my curiousity, I did more analysis on it and finally figure out where the system fetched all these module files according to my xorg log until, I found out more undocumented driver modules available that can be loaded into config files.
All of these modules can be fetch from /usr/lib/xorg/modules
glamor 212.0 kb
int10 142.6 kb
wfb 134.9 kb
fb 110.9 kb
exa 94.7 kb
shadow 38.1 kb
gahw 35.1 kb
vbe 30.3 kb
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