OK, thanks. Meanwhile I found the old machine with Atom N450, installed Leap 15.0 freshly on it, and could reproduce a similar problem. Then I tried to revert a few patches, and it seems that the key commit is 9b27390139dbe0dc10d1899545248862fe826b61 drm/i915: Use the correct crtc when sanitizing plane mapping Reverting this one together with the commit in comment 4 made the graphics working again. Now I pushed two reverts to SLE15 branch.