[Bug 94605] [SKL] Flashing black screen ([drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94605

--- Comment #81 from Mauro Santos <registo.mailling at gmail.com> ---
(In reply to Peter Wu from comment #80)
> Under what circumstances? Any special cmdline, patches or userspace
> packages? So far it seems to work for me (i7-6700HQ, Arch Linux, 4.8.6-1).

I'm also on Arch with kernel 4.8.6-1. I have an i7-6500U.

I guess the only "special" thing I have on the cmdline is intel_iommu=on, but I
don't see any memory errors as reported by syphyr.

I have a way to avoid the problems, but that will limit the package c-state to
PC2, let me try to explain.

If I do not do modifications to any of the kernel's defaults, the cpu never
gets to a package c-state lower than PC2 (1)(or higher, whichever way you want
to see it).

If I enable sata ALPM then the cpu will to go into PC6 and that is when I start
to see the problem.

Further, if I turn on auto suspend for a usb bluetooth device, the cpu will now
get into PC7 and I also see the problem in this case. I have not been able to
get the cpu to go into PC8~PC10 even when doing all the changes recommended by
powertop.

(1) The cpu's datasheet states clearly that "Long term reliability cannot be
assured unless all the Low-Power Idle States are enabled.". I'm not sure if
this applies to package c-states but even if it doesn't I would like the cpu to
be as efficient as possible so that I get more time when using battery and so
that there is less heat and noise.

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