Regression in v4.8-rc4: i915 flickering since commit 1c80c25fb6

[Dominik Brodowski]

Hi!

Since commit 1c80c25fb6 (determined by git bisect, and confirmed by
reverting this patch on top of 9ca581b50d), the sceen on my DELL XPS 13
is flickering every once in a while (sometimes multiple times per
second, sometimes only every few seconds).

That's for

00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09) (prog-if 00 [VGA controller])
        Subsystem: Dell Device 0665
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin A routed to IRQ 42
        Region 0: Memory at f6000000 (64-bit, non-prefetchable) [size=16M]
        Region 2: Memory at e0000000 (64-bit, prefetchable) [size=256M]
        Region 4: I/O ports at f000 [size=64]
        [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: i915

and Debian Jessie userland.

Best,
	Dominik