Linux Kernel 4.4.0-66 Possible DRM connector_status Bug For LG Displays

Deucher, Alexander Alexander.Deucher at
Wed May 31 16:48:08 UTC 2017

Use git to bisect between the current problematic kernel and the last working kernel.  Bisecting is a git feature that allows you to bisect the commits between two points to determine what change caused the regression.  Google for "git bisect howto".


From: Tom Reddish [mailto:tom.reddish at]
Sent: Wednesday, May 31, 2017 12:44 PM
To: Deucher, Alexander
Cc: Koenig, Christian; amd-gfx at; Brian Kane
Subject: Re: Linux Kernel 4.4.0-66 Possible DRM connector_status Bug For LG Displays

What do you mean by bisect?

My gut is telling me it's something that changed in the kernel. Maybe the kernel is correctly parsing the information it is being given from the display now and in the older kernel it was handling that information differently? With the exact same display and no settings changed on it if I use the older kernel it shows up as connected

Tom Reddish
Software Engineer
MediaVue Systems
Skype: t.reddish
Tel: +1 781.926.0676

On May 31, 2017, at 12:24 PM, Deucher, Alexander <Alexander.Deucher at<mailto:Alexander.Deucher at>> wrote:

Can you bisect?  Sounds like the monitor does not keep the EDID powered up when the display is off as is required by the vesa spec.


From: Tom Reddish [mailto:tom.reddish at]
Sent: Wednesday, May 31, 2017 12:20 PM
To: Deucher, Alexander; Koenig, Christian
Cc: amd-gfx at<mailto:amd-gfx at>; Brian Kane
Subject: Linux Kernel 4.4.0-66 Possible DRM connector_status Bug For LG Displays

LG Displays are being reported as "disconnected" when they are powered off (currently connected through DVI to mini-displayport adapter)

Only seeing this with LG displays (have tested NEC and Samsung *limited model types for each manufacturer*). With the LG display connected to the graphics card and powered off the system is reporting the DisplayPort as disconnected. In any kernel <= 4.4.0-31 the system would report the DisplayPort as connected even if the LG display was off.

Kernel tested on
Linux version 4.4.0-66-generic (buildd at lgw01-28) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4) ) #87-Ubuntu

Most recent kernel without the bug:
Linux version 4.4.0-31-generic (buildd at lgw01-16) (gcc version 5.3.1 20160413 (Ubuntu 5.3.1-14ubuntu2.1) ) #50-Ubuntu

"cat /sys/class/drm/card1-DP-1/status" will show the status as disconnected if the LG display is powered off

          Ubuntu 16.04
          Graphics Card: Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
          Radeon Graphics Drivers
          Kernel: 4.4.0-66

processor       : 0-3
vendor_id      : AuthenticAMD
cpu family     : 21
model                        : 48
model name   : AMD A8-7600 Radeon R7, 10 Compute Cores 4C+6G
stepping         : 1
microcode      : 0x6003106
cpu MHz                   : 1400.000
cache size      : 2048 KB
physical id     : 0
siblings          : 4
core id                       : 0
cpu cores       : 2
apicid             : 16
initial apicid   : 0
fpu                 : yes
fpu_exception           : yes
cpuid level     : 13
wp                 : yes
flags               : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc extd_apicid aperfmperf eagerfpu pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 popcnt aes xsave avx f16c lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt lwp fma4 tce nodeid_msr tbm topoext perfctr_core perfctr_nb bpext cpb hw_pstate vmmcall fsgsbase bmi1 xsaveopt arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold
bugs               : fxsave_leak sysret_ss_attrs
bogomips       : 6188.48
TLB size        : 1536 4K pages
clflush size     : 64
cache_alignment        : 64
address sizes  : 48 bits physical, 48 bits virtual
power management: ts ttp tm 100mhzsteps hwpstate cpb eff_freq_ro [13]

Loaded driver and hardware information
cat /proc/ioports:
0000-03af : PCI Bus 0000:00
  0000-001f : dma1
  0020-0021 : pic1
  0040-0043 : timer0
  0050-0053 : timer1
  0060-0060 : keyboard
  0061-0061 : PNP0800:00
  0064-0064 : keyboard
  0070-0071 : rtc0
  0080-008f : dma page reg
  00a0-00a1 : pic2
  00c0-00df : dma2
  00f0-00ff : PNP0C04:00
    00f0-00ff : fpu
03b0-03df : PCI Bus 0000:00
  03c0-03df : vesafb
03e0-0cf7 : PCI Bus 0000:00
  03f8-03ff : serial
  040b-040b : pnp 00:08
  04d0-04d1 : pnp 00:07
    04d0-04d1 : pnp 00:08
  04d6-04d6 : pnp 00:08
  0800-0803 : ACPI PM1a_EVT_BLK
  0804-0805 : ACPI PM1a_CNT_BLK
  0808-080b : ACPI PM_TMR
  0810-0815 : ACPI CPU throttle
  0820-0827 : ACPI GPE0_BLK
  0900-090f : pnp 00:08
  0910-091f : pnp 00:08
  0a00-0a0f : pnp 00:03
    0a00-0a07 : f71882fg
  0a10-0a1f : pnp 00:03
  0b00-0b07 : piix4_smbus
  0b20-0b3f : pnp 00:08
    0b20-0b27 : piix4_smbus
  0c00-0c01 : pnp 00:08
  0c14-0c14 : pnp 00:08
  0c50-0c51 : pnp 00:08
  0c52-0c52 : pnp 00:08
  0c6c-0c6c : pnp 00:08
  0c6f-0c6f : pnp 00:08
  0cd0-0cd1 : pnp 00:08
  0cd2-0cd3 : pnp 00:08
  0cd4-0cd5 : pnp 00:08
  0cd6-0cd7 : pnp 00:08
  0cd8-0cdf : pnp 00:08
0cf8-0cff : PCI conf1
0d00-ffff : PCI Bus 0000:00
  d000-dfff : PCI Bus 0000:02
    d000-d0ff : 0000:02:00.0
      d000-d0ff : r8169
  e000-efff : PCI Bus 0000:01
    e000-e0ff : 0000:01:00.0
  f000-f0ff : 0000:00:01.0
  f100-f10f : 0000:00:11.0
    f100-f10f : ahci
  f110-f113 : 0000:00:11.0
    f110-f113 : ahci
  f120-f127 : 0000:00:11.0
    f120-f127 : ahci
  f130-f133 : 0000:00:11.0
    f130-f133 : ahci
  f140-f147 : 0000:00:11.0
    f140-f147 : ahci
  fe00-fefe : pnp 00:08

PCI Information
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] (prog-if 00 [VGA controller])
          Subsystem: Hightech Information System Ltd. Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
          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: 64 bytes
          Interrupt: pin A routed to IRQ 48
          Region 0: Memory at c0000000 (64-bit, prefetchable) [size=256M]
          Region 2: Memory at fea00000 (64-bit, non-prefetchable) [size=256K]
          Region 4: I/O ports at e000 [size=256]
          Expansion ROM at fea40000 [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 256 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- ASPMOptComp+
                      LnkCtl:            ASPM Disabled; RCB 64 bytes Disabled- CommClk+
                                  ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
                      LnkSta:           Speed 8GT/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: 0000
          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: [200 v1] #15
          Capabilities: [270 v1] #19
          Kernel driver in use: radeon
          Kernel modules: radeon

Tom Reddish
Software Engineer
MediaVue Systems
Skype: t.reddish
Tel: +1 781.926.0676

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