Skylake+ freezes after 311770173fac27845a3a83e2c16100a54d308f72
Somewhere between 5.4 and 5.5, a change was introduced that caused frequent system hangs on my Skylake system. These hangs are terrible to diagnose, since they simply leave no trace (there are no dmesg logs / stack traces at all, even when resorting to netconsole / pstore). So over the last few weeks, I've been slowly bisecting the 5.4->5.5 transition, and have arrived at the following culprit with reasonably high confidence:
311770173fac27845a3a83e2c16100a54d308f72 drm/i915/gt: Schedule request retirement when timeline idles
The immediately preceding commit has never hanged here, and this commit -- and every subsequent commit up to the latest drm-tip (20200229) -- has caused hangs repeatedly, usually not longer than a couple of hours after booting.
This seems to suggest that #614 has not been properly fixed.
Since this appears related to RC6 power states (whose disabling has been disabled, cf. #100 (closed)), I would personally take a workaround that simply disabled RC6 power states, as that appears related to the problem here.