i915: occasional hangs on Baytrail with deeper C-states

Daniel Bilik ddb at neosystem.org
Wed Mar 2 08:06:47 PST 2016


(This is not really a bugreport, just a notice to inform potential
victims. :) AFAICT it's not DragonFly specific issue, see below.)

I'm experiencing occasional freezes running DragonFly desktop on a
Baytrail system (namely Intel Celeron J1900) with machdep.mwait.CX.idle
set to AUTODEEP (which enables C6 and C7 on this system). Limiting it to
C1/1 makes the system stable.

Interestingly, the problem is evolving somewhat... The system was stable
before commit 2c9916c+ (drm/i915: Upgrade to Linux 4.0). After this update
I started to experience the hangs, approximately once a day. I didn't know
about the "C1 workaround" at that time, so I just locally reverted that
commit to get the stable system. Commit 477eb7f+ (drm/i915: Update to
Linux 4.1) somehow fixed it, and system was stable again, even with
machdep.mwait.CX.idle=AUTODEEP. But commit 19c468b+ (drm/i915: Update to
Linux 4.2) brought the hangs back, and this time I've "resolved" it via

According to these bugreports from linux users...


... it doesn't seem to be DragonFly specific issue but more probably a bug
in shared i915 code. Those discussions also confirm that bug was
introduced somewhere after linux 3.16, then disappeared for a while during
4.1 and was brought back with 4.2 (and remains to 4.5). So far, nobody has
come with a solution, but everyone confirm that "C1 workaround" prevents
from hangs.



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