https://bugs.freedesktop.org/show_bug.cgi?id=93895
--- Comment #6 from Azari azari4096@gmail.com --- I have something new to report after doing more testing.
It seems that if I launch weston with the pixman backend (weston --use-pixman), that works, but meanwhile, startx with 'exec twm' in .xinitrc doesn't work on first attempt, it causes the lockup.
However, after the lockup, if i try to startx again (still with twm), it suddenly works and i can start applications in twm and use the desktop. I managed to reproduce this with Xfce as well, the first 'startxfce4' after bootup will fail and lockup the GPU, and after it resets, I try again and Xfce works.
One thing of note is that when I finally do manage to get a DE started (after the GPU has locked up and reset once), glxinfo shows only "gallium on llvmpipe"; no hardware acceleration available.
So whatever is causing the lockup is something that X does at startup (even when a minimal X window manager like twm is used), but weston-pixman doesn't do.