[Bug 88012] [bisected BYT] complete freeze after: drm/i915/vlv: WA for Turbo and RC6 to work together

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=88012

--- Comment #31 from Jesse Barnes <jbarnes at virtuousgeek.org> ---
Juergen sounds certain that this commit affects this issue, and I can believe
it.

The punit provides several services, including CPU and GPU power management,
and the code in question changes how we interact with the Punit to a degree.

So it's possible a BIOS upgrade (which would include a new Punit firmware)
might help.

It's also possible that we're not validating the result of Deepak's code enough
and end up feeding some bad values to the Punit as as result of the new
calculations.

Or the simple fact that we're reading a new Punit reg fairly frequently is
enough to cause trouble.  In that case, throttling the vlv_c0_residency reads
of the CZ timestamp may be enough to avoid this.  (I don't think the C0 count
reads should cause trouble, but it's possible they trigger additional punit
activity as well, just by being enabled for read out in the control reg.)

Deepak, Ben, or Chris, any other ideas?

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