How to force GNOME to use Wayland?

Question

TL;DR

gnome-shell does not want to be a Wayland compositor.

Edit: Sometimes it does want to be, sometimes it doesn't.

Log

Dec 31 06:55:26 speedy-desktop gnome-shell[393]: Can't initialize KMS backend: could not find drm kms device
Dec 31 06:55:29 speedy-desktop /usr/lib/gdm/gdm-x-session[410]: (II) [KMS] Kernel modesetting enabled.

I have 2 video cards. (See LSPCI below)

Extended Problem

I've been told that GNOME uses Wayland by default. But for some reason, I don't know how to get them to work together. Arch wiki just mentions the usage of weston and the GDM & GNOME pages don't say anything about wayland... only the GNOME page, but that's only for manual startup.

⚡ loginctl show-session c6 -p Type 
Type=x11 -- GDM

⚡ loginctl show-session c7 -p Type
Type=x11 -- GNOME

Tries

1. Putting export XDG_SESSION_TYPE=wayland to /etc/profile => no result

2. Reinstalling the gnome group (yaourt -S gnome) => messed up my NetworkManager, but I fixed that myself.

3. Launching weston from an X session => works, but weston-launch from a tty hanged my PC... (I can't find logs, if you can comment their path, I'll post them, journalctl -xe doesn't seem to contain anything wayland-or-weston-related)

   The only thing I did find in journalctl -xe -b -1 is this:

   Dec 31 07:18:08 speedy-desktop kernel: radeon_dp_aux_transfer_native: 158 callbacks suppressed
   

4. Put MUTTER_ALLOW_HYBRID_GPUS=1 to /etc/environment => no result

Almost working...

I was looking through the journal, and... what did I find?

Dec 31 04:31:57 speedy-desktop /usr/lib/gdm/gdm-wayland-session[382]: /usr/lib/gio/modules/libgvfsdbus.so: file too short
Dec 31 04:31:57 speedy-desktop /usr/lib/gdm/gdm-wayland-session[382]: Failed to load module: /usr/lib/gio/modules/libgvfsdbus.so

The file wasn't simply short, it was EMPTY. How? I have no idea.

After lots of g00gling it turned out that my pacman database was corrupt (somehow), and this one-liner (posted here) fixed it.

LANG= pacman -Qkk 2>&1 | grep "^.*: no mtree file$" | cut -d: -f1 | sudo xargs pacman -S --force --noconfirm

BUT GNOME still uses X11. I have absolutely no idea why. Here's the problem:

Dec 31 06:55:26 speedy-desktop gnome-shell[393]: Can't initialize KMS backend: could not find drm kms device
Dec 31 06:55:29 speedy-desktop /usr/lib/gdm/gdm-x-session[410]: (II) [KMS] Kernel modesetting enabled.

X server knows that there is KMS, but gnome-shell doesn't?! What?

Configs?

DEFAULT. I simply haven't touched them. (Or at least I have reversed my modifications)

LSPCI

⚡ lspci | grep VGA
00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Trinity [Radeon HD 7560D]
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]

Any help is appreciated!

PS: Just ran yaourt -Syu a couple seconds ago.

Answer 1

I had a similar problem width GDM ("Just FYI, it now works... Partially. Sometimes it starts wayland, sometimes X") and to solve my problem I had to add a driver card module to my mkinitcpio config file. Was something to do with concurrency load with systemd or something like that. Im not an expert so i really dont know. something like this (i915 for intel or nouveau for nvidia):

in /etc/mkinitcpio.conf

MODULES=(... i915 ...)

and then run:

# mkinitcpio