[Bug 97985] [BDW] System hang while running Qt QML application, with unclaimed registers

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97985

--- Comment #15 from Anssi Hannula <anssi.hannula at bitwise.fi> ---
Some additional details:

- Setting the DDX option "VSync" to off seems to workaround the issue, so I
guess the issue is indeed vblank related as per comment #10. So far I've run
the problematic case on 4.4.22 (not tested with nightly yet) for several hours
and I have gotten no freezes and no "unclaimed register" warnings with VSync
off (with no other workarounds active).

- If I use the modesetting DDX (with glamor), the problem does not seem to
appear (no warnings, no hang, on 4.4.22). Judging from the tearing I see I
guess VSync is just not getting used (at least with my versions of everything)
so this is in effect the same as disabling VSync.

- "intel_idle.max_cstate=2" (2 = C1E-BDW) does not produce a hang with a ~12h
run, but does produce the unclaimed register warnings.
"intel_idle.max_cstate=3" (3 = C3-BDW) does also produce the hang.

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