Experiencing FIFO underruns on Intel Skylake platform

[Rainer Koenig]

Hi,

I'm testing the vanilla kernel on prototype boards for Intel Skylake.
The graphics adapter on those boards identifies like this:

00:02.0 0300: 8086:1912 (rev 04) (prog-if 00 [VGA controller])
	Subsystem: 1734:121c
	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 123
	Region 0: Memory at d0000000 (64-bit, non-prefetchable) [size=16M]
	Region 2: Memory at c0000000 (64-bit, prefetchable) [size=256M]
	Region 4: I/O ports at f000 [size=64]
	Expansion ROM at <unassigned> [disabled]
	Capabilities: [40] Vendor Specific Information: Len=0c <?>
	Capabilities: [70] Express (v2) Root Complex Integrated Endpoint, MSI 00
		DevCap:	MaxPayload 128 bytes, PhantFunc 0
			ExtTag- RBE+
		DevCtl:	Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
			RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
			MaxPayload 128 bytes, MaxReadReq 128 bytes
		DevSta:	CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr- TransPend-
		DevCap2: Completion Timeout: Not Supported, TimeoutDis-, LTR-, OBFF
Not Supported
		DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF
Disabled
	Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
		Address: fee00018  Data: 0000
	Capabilities: [d0] Power Management version 2
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [100 v1] #1b
	Capabilities: [200 v1] Address Translation Service (ATS)
		ATSCap:	Invalidate Queue Depth: 00
		ATSCtl:	Enable-, Smallest Translation Unit: 00
	Capabilities: [300 v1] #13
	Kernel driver in use: i915
	Kernel modules: i915


I'm running both Fedora 21 and OpenSUSE 13.2 on those boards at the
moment, both with a self compiled Kernel 4.1-rc4 (latest git pull was
today).

Problem: Whenever power management kicks in and blanks the screen the
systems behave very strange when trying to get the screen back. The
screen is not fully restored then, but when I move the mouse (Gnome 3 or
XFCE desktops) up and down the image rolls up and down like a curtain. I
see no mouse cursor anymore and can't resume to normal operation.

When this happens I see the following line in dmesg:

[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO
underrun

Hardware is still the first prototypes for Skylake, BIOS is beta too.
But I wanted to give a note about that problem here, maybe someone has
an idea what is missing.

Regards
Rainer
-- 
Dipl.-Inf. (FH) Rainer Koenig
Project Manager Linux Clients
Dept. PDG WPS R&D SW OSE

Fujitsu Technology Solutions
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Germany

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