[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 #83 from syphyr at gmail.com ---
(In reply to Mauro Santos from comment #81)
> (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.

Could you try replacing "intel_iommu=on" with:
intel_iommu=igfx_off

I also still have problems with intel_iommu=on.

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