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

Deucher, Alexander Alexander.Deucher at
Wed May 31 16:24:30 UTC 2017

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; 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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