Random hangs from unnoticable to system freeze
These hangs are usually noted in my .xsession-errors log and start out like this
nouveau: kernel rejected pushbuf: Cannot allocate memory
I'm not sure whether this is the relevant log entry but it always accompanies these hangs. The effect ranges from not noticable, over plasma hanging for a while, but apps still usable, to complete freeze without even the mouse moving. Luckily, in can still get in via SSH and examine things and shut the system down. The main problem is that this renders the system useless, because there's no way of knowing when it strikes. Prusaslicer is a good candidate for triggering errors on 4.15 kernel, but now it seems vivaldi is better at it.
I'm running kde neon 5.19 and had this problem with the ubuntu 4.15 kernel. I went ahead and built a fresh kernel using the linux-5.5 branch of https://github.com/skeggsb/linux.git.
There the problem is happening, too. Then i went ahead and followed https://nouveau.freedesktop.org/InstallNouveau.html to build the user land dependencies as described there except for using meson instead of autotools for libdrm, mesa and libvdpau.
BTW. i translated the mesa autogen call to the following
meson out/ -Dprefix=$NVD \ -Dgles1=true \ -Dgles2=true \ -Dglx=auto \ -Degl=true \ -Dshared-glapi=true \ -Dgbm=true \ -Dosmesa=true \ -Dplatforms=x11 \ -Dgallium-drivers=nouveau,swrast \ -Ddri-drivers=nouveau
Not sure whether that's right, but it built, installed and ran.