i915: occasional hangs on Baytrail with deeper C-states

Daniel Bilik ddb at neosystem.org
Sat Apr 2 05:13:17 PDT 2016


Another follow-up... The story has got famous already:


But regardless pessimistic tone of the article, there are also good news,
at least for me. :)

The problem commit that introduced freezes was bisected to this:


In fact, it was mentioned earlier in bugzilla.kernel.org disscussion, but
I've missed it in those hundreds of comments.

And now good news. Mika Kuoppala has come with tentative patches...


... that solve stability issues on my system. Diff against recent
DragonFly sources is attached.

I'm running this on my Baytrail system for a week now, with C6 and C7
enabled, and without a single freeze. Previously, it was freezing at least
each second day, sometimes two or three times a day.

If I read it correctly, the problem commit introduced "aggressive"
re-clocking on Valleyview, removing some specific thresholds. And
Mika's patches bring those "sane" thresholds back, in a different way,
with some additional safebelts. It touches just Valleyview-specific code
and should not affect driver behaviour on other chips. AFAICT it can
be safely imported to DragonFly, but Francois Tigeot may comment it

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