With newer kernels, display resolutions under 60Hz the attached monitors (tried multiple with multiple modes on DVI and display port) fail to sync.

Working kernel: 3.16.0-4-amd64 (Debian)

Non working: 4.1.0 (Debian), and 4.3.0-rc6 (mainline).

My main monitor is a 4k resolution monitor which will only supports 30Hz at the default full native resolution.

[   14.102283] [drm] radeon kernel modesetting enabled.
[   14.103946] radeon 0000:01:00.0: VRAM: 1024M 0x0000000000000000 - 0x000000003FFFFFFF (1024M used)
[   14.104022] radeon 0000:01:00.0: GTT: 1024M 0x0000000040000000 - 0x000000007FFFFFFF
[   14.105476] [drm] radeon: 1024M of VRAM memory ready
[   14.105672] [drm] radeon: 1024M of GTT memory ready.
[   14.108782] radeon 0000:01:00.0: firmware: direct-loading firmware radeon/REDWOOD_pfp.bin
[   14.109799] radeon 0000:01:00.0: firmware: direct-loading firmware radeon/REDWOOD_me.bin
[   14.114441] radeon 0000:01:00.0: firmware: direct-loading firmware radeon/REDWOOD_rlc.bin
[   14.117105] radeon 0000:01:00.0: firmware: direct-loading firmware radeon/REDWOOD_smc.bin
[   14.143419] [drm] radeon: dpm initialized
[   14.144488] radeon 0000:01:00.0: firmware: direct-loading firmware radeon/CYPRESS_uvd.bin
[   14.145853] [drm] enabling PCIE gen 2 link speeds, disable with radeon.pcie_gen2=0
[   14.154866] radeon 0000:01:00.0: WB enabled
[   14.154910] radeon 0000:01:00.0: fence driver on ring 0 use gpu addr 0x0000000040000c00 and cpu addr 0xffff88033072ac00
[   14.154975] radeon 0000:01:00.0: fence driver on ring 3 use gpu addr 0x0000000040000c0c and cpu addr 0xffff88033072ac0c
[   14.155929] radeon 0000:01:00.0: fence driver on ring 5 use gpu addr 0x000000000005c418 and cpu addr 0xffffc9000241c418
[   14.156093] radeon 0000:01:00.0: radeon: MSI limited to 32-bit
[   14.156159] radeon 0000:01:00.0: radeon: using MSI.
[   14.156242] [drm] radeon: irq initialized.
[   15.443703] fbcon: radeondrmfb (fb0) is primary device                                                                                                                                
[   15.669263] radeon 0000:01:00.0: fb0: radeondrmfb frame buffer device
[   15.669288] radeon 0000:01:00.0: registered panic notifier
[   15.679661] [drm] Initialized radeon 2.43.0 20080528 for 0000:01:00.0 on minor 0



01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Redwood XT GL [FirePro V4800] (prog-if 00 [VGA controller])
        Subsystem: Dell Device 240a
        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: 32 bytes
        Interrupt: pin A routed to IRQ 49
        Region 0: Memory at d0000000 (64-bit, prefetchable) [size=256M]
        Region 2: Memory at fbce0000 (64-bit, non-prefetchable) [size=128K]
        Region 4: I/O ports at c000 [size=256]
        Expansion ROM at fbcc0000 [disabled] [size=128K]
        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 5GT/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: Range ABCD, TimeoutDis+, LTR-, OBFF Not Supported
                DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled
                LnkCtl2: Target Link Speed: 5GT/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: 00000000feeff00c  Data: 4172
        Capabilities: [100 v1] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
        Capabilities: [150 v1] 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-
        Kernel driver in use: radeon