dp blanks randomly with errors

[Christopher Barry]

Getting these errors in syslog

[drm:radeon_dp_link_train_ce] *ERROR* displayport link status failed
[drm:radeon_dp_link_train_ce] *ERROR* channel eq failed

also, there have been a lot of 'clock recovery failed' errors as well.

running debian sid, and I upgrade about every 5 days or so, so my box
is quite up to date for a packaged distro. I upgraded this afternoon
EST and behavior is still bad.

debian packaged kernel 2.14.2

X.Org X Server 1.16.2.901 (1.16.3 RC 1)
Release Date: 2014-12-09
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.2.0-4-amd64 x86_64 Debian
Current Operating System: Linux monolith 3.12-1-amd64 #1 SMP Debian
3.12.9-1 (2014-02-01) x86_64
Kernel command line: BOOT_IMAGE=/vmlinuz-3.12-1-amd64
root=/dev/mapper/system_vg-os_lv ro quiet
Build Date: 09 December 2014  10:15:28PM
xorg-server 2:1.16.2.901-1 (http://www.debian.org/support) 
Current version of pixman: 0.32.6
	Before reporting problems, check http://wiki.x.org
	to make sure that you have the latest version.


lspci -vv for video card:

02:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
[AMD/ATI] Pitcairn PRO [Radeon HD 7850] (prog-if 00 [VGA controller])
Subsystem: PC Partner Limited / Sapphire Technology Radeon HD 7850 2GB
GDDR5 DVI-I/DVI-D/HDMI/DP 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, Cache Line Size: 256 bytes
Interrupt: pin A routed to IRQ 56 Region 0: Memory at d0000000 (64-bit,
prefetchable) [size=256M] Region 2: Memory at fb9c0000 (64-bit,
non-prefetchable) [size=256K] Region 4: I/O ports at b000 [size=256]
Expansion ROM at fb9a0000 [disabled] [size=128K] Capabilities: [48]
Vendor Specific Information: Len=08 <?> Capabilities: [50] Power
Management version 3 Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA
PME(D0-,D1+,D2+,D3hot+,D3cold-) Status: D0 NoSoftRst- PME-Enable-
DSel=0 DScale=0 PME- Capabilities: [58] Express (v2) Legacy Endpoint,
MSI 00 DevCap: MaxPayload 256 bytes, PhantFunc 0, Latency L0s <4us, L1
unlimited ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset-
                DevCtl: Report errors: Correctable- Non-Fatal- Fatal-
Unsupported- RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop+
                        MaxPayload 128 bytes, MaxReadReq 512 bytes
                DevSta: CorrErr+ UncorrErr- FatalErr- UnsuppReq+
AuxPwr- TransPend- LnkCap: Port #0, Speed 8GT/s, Width x16, ASPM L0s
L1, Exit Latency L0s <64ns, L1 <1us ClockPM- Surprise- LLActRep- BwNot-
                LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- CommClk+
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
                LnkSta: Speed 5GT/s, Width x16, TrErr- Train- SlotClk+
DLActive- BWMgmt- ABWMgmt- DevCap2: Completion Timeout: Not Supported,
TimeoutDis-, LTR-, OBFF Not Supported DevCtl2: Completion Timeout: 50us
to 50ms, TimeoutDis-, LTR-, OBFF Disabled LnkCtl2: Target Link Speed:
8GT/s, EnterCompliance- SpeedDis- Transmit Margin: Normal Operating
Range, EnterModifiedCompliance- ComplianceSOS- Compliance De-emphasis:
-6dB LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete-,
EqualizationPhase1- EqualizationPhase2-, EqualizationPhase3-,
LinkEqualizationRequest- Capabilities: [a0] MSI: Enable+ Count=1/1
Maskable- 64bit+ Address: 00000000fee00000  Data: 4023
        Capabilities: [100 v1] Vendor Specific Information: ID=0001
Rev=1 Len=010 <?> Capabilities: [150 v2] Advanced Error Reporting
                UESta:  DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt-
UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol- UEMsk:  DLP- SDES-
TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq-
ACSViol- UESvrt: DLP+ SDES+ TLP- FCP+ CmpltTO- CmpltAbrt- UnxCmplt-
RxOF+ MalfTLP+ ECRC- UnsupReq- ACSViol- CESta:  RxErr- BadTLP- BadDLLP-
Rollover- Timeout- NonFatalErr+ CEMsk:  RxErr- BadTLP- BadDLLP-
Rollover- Timeout- NonFatalErr+ AERCap: First Error Pointer: 00,
GenCap+ CGenEn- ChkCap+ ChkEn- Capabilities: [270 v1] #19 Capabilities:
[2b0 v1] Address Translation Service (ATS) ATSCap: Invalidate Queue
Depth: 00 ATSCtl: Enable-, Smallest Translation Unit: 00
        Capabilities: [2c0 v1] #13
        Capabilities: [2d0 v1] #1b
        Kernel driver in use: radeon

(pardon the wrapping)

starting last week sometime, my displayport driven monitor (center of 3
monitors) began randomly blanking out. The only way to (sometimes)
correct it for maybe 2 or three hours was to power down, then power up.
if I just rebooted, it would almost always blank in a matter of minutes
after login.

I am converting the DP into DVI with an active dongle, but this has
worked flawlessly for me in the past.

I started booting the last debian kernel, which is 3.12.2, and so far
the blanking has not re-appeared. I think I probably need to run this
kernel for a couple of days to verify that it is somehow related to a
software change to be sure my dongle is not really flaking out,
but thought I would post a heads up here in case anyone might know of
any changes that may have caused this behavior.

-C