GPU compatibility with Linux-libre

[Bone Baboon]

This is a summary of what I have learned about GPU compatibility with
Linux-libre from the help I received in these email threads: 

Start Xorg server using xinit manually
https://lists.gnu.org/archive/html/help-guix/2021-03/msg00197.html

Two more computers unable to start X with GDM
https://lists.gnu.org/archive/html/help-guix/2021-03/msg00250.html

Starting Sway a Wayland window manager
https://lists.gnu.org/archive/html/help-guix/2021-03/msg00268.html

Corrections or further information is appreciated.

Testing was done on two i686 computers and three x86_64 computers.

1) After installing the Guix operating system on a computer check if the
directory /dev/dri/ exists.
** If it does *not* exist then your computer's GPU is *not* compatible
   with Linux-libre.
** If it does exist then your computer's GPU is compatible with
   Linux-libre.

2) If your GPU is not compatible with Linux-libre (see 1 above) then
Xorg server and Wayland window managers will not work.

3) If your GPU is compatible with Linux-libre (see 1 above) but you have
trouble getting Xorg server to work consider using a Wayland window
manager.  I was able to get Sway a Wayland window manager working on a
computer that Xorg server was not working with.

Note: If you use a Wayland window manager some programs that work with
Xorg server may not work.  There may be alternatives programs for those
that do not work.  I found this helpful:
https://github.com/natpen/awesome-wayland