kern/60529: kernel output lost when using DVI connected monitor

["sjg%crufty.net@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60529
>Category:       kern
>Synopsis:       kernel output lost when using DVI connected monitor
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Aug 02 03:55:00 +0000 2026
>Originator:     Simon Gerraty
>Release:        11.0-RC6
>Organization:
>Environment:
NetBSD bad.crufty.net 11.0_RC6 NetBSD 11.0_RC6 (GENERIC) #0: Tue Jul  7 15:10:39 UTC 2026  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
In an effort to save space, I setup a HDMI kvm so that two machines could share the same monitor and usb keyboard.
On "bad" I used a DVI to HDMI adaptor.
While booting I could see BIOS flash screen and EFI loader output, and I could interact with the loader ok.

Once the kernel itself started booting I lost all video output.
The machine came up to the point where it was pingable, but I was not able
to login via ssh.

I had to power off the box so I could reconnect the VGA monitor.
When booting I could see the BIOS flash screen and EFI loader output on both displays, but once the kernel started booting I lost all video on both displays.
Again the box booted to the point of being pingable, but could not login via ssh.

Unplugging the HDMI cable at the KVM end and reboot did not help.
Unplugging the HDMI cable from the DVI adaptor and reboot, the VGA display showed kernel output and the box booted normally.

Since I had to power the box off to move it to access the monitor connections I do not have any dmesg output from when the HDMI was connected to monitor.

FWIW below is dmesg with VGA console only

Copyright (c) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
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    2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023,
    2024, 2025, 2026
    The NetBSD Foundation, Inc.  All rights reserved.
Copyright (c) 1982, 1986, 1989, 1991, 1993
    The Regents of the University of California.  All rights reserved.

NetBSD 11.0_RC6 (GENERIC) #0: Tue Jul  7 15:10:39 UTC 2026
        mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC
total memory = 3993 MB
avail memory = 3832 MB
timecounter: Timecounters tick every 10.000 msec
Kernelized RAIDframe activated
timecounter: Timecounter "i8254" frequency 1193182 Hz quality 100
efi: systbl at pa bdb87f18
mainbus0 (root)
ACPI: RSDP 0x00000000BDB5BF98 000024 (v02 INTEL )
ACPI: XSDT 0x00000000BDB5AE18 00004C (v01 INTEL  DG43NB   0000005A MSFT 00010013)
ACPI: FACP 0x00000000BDB59D98 0000F4 (v04 INTEL  DG43NB   06222004 MSFT 00010013)
ACPI: DSDT 0x00000000BDB54018 004E89 (v01 INTEL  DG43NB   0000005A INTL 20051117)
ACPI: FACS 0x00000000BDB5DF40 000040
ACPI: FACS 0x00000000BDB62F40 000040
ACPI: APIC 0x00000000BDB59F18 00006C (v02 INTEL  DG43NB   0000005A MSFT 00010013)
ACPI: MCFG 0x00000000BDB64E18 00003C (v01 INTEL  DG43NB   0000005A MSFT 00000097)
ACPI: ASF! 0x00000000BDB63D18 0000A0 (v32 INTEL  DG43NB   0000005A TFSM 000F4240)
ACPI: HPET 0x00000000BDB64D98 000038 (v01 INTEL  DG43NB   0000005A AMI. 00000003)
ACPI: 1 ACPI AML tables successfully acquired and loaded
ioapic0 at mainbus0 apid 0: pa 0xfec00000, version 0x20, 24 pins
cpu0 at mainbus0 apid 0
cpu0: Use lfence to serialize rdtsc
cpu0: Intel(R) Core(TM)2 Quad CPU    Q9550  @ 2.83GHz, id 0x1067a
cpu0: node 0, package 0, core 0, smt 0
cpu1 at mainbus0 apid 1
cpu1: Intel(R) Core(TM)2 Quad CPU    Q9550  @ 2.83GHz, id 0x1067a
cpu1: node 0, package 0, core 1, smt 0
cpu2 at mainbus0 apid 2
cpu2: Intel(R) Core(TM)2 Quad CPU    Q9550  @ 2.83GHz, id 0x1067a
cpu2: node 0, package 0, core 2, smt 0
cpu3 at mainbus0 apid 3
cpu3: Intel(R) Core(TM)2 Quad CPU    Q9550  @ 2.83GHz, id 0x1067a
cpu3: node 0, package 0, core 3, smt 0
acpi0 at mainbus0: Intel ACPICA 20241212
acpi0: X/RSDT: OemId < INTEL,  DG43NB,0000005a>, AslId <MSFT,00010013>
acpi0: MCFG: segment 0, bus 0-255, address 0x00000000e0000000
acpi0: SCI interrupting at int 9
acpi0: fixed power button present
timecounter: Timecounter "ACPI-Fast" frequency 3579545 Hz quality 1000
hpet0 at acpi0: high precision event timer (mem 0xfed00000-0xfed00400)
timecounter: Timecounter "hpet0" frequency 14318180 Hz quality 2000
MCH (PNP0C01) at acpi0 not configured
com0 at acpi0 (UAR1, PNP0501-1): io 0x3f8-0x3ff irq 4
com0: ns16550a, 16-byte FIFO
attimer1 at acpi0 (TMR, PNP0100): io 0x40-0x43 irq 0
pcppi1 at acpi0 (SPKR, PNP0800): io 0x61
spkr0 at pcppi1: PC Speaker
wsbell at spkr0 not configured
midi0 at pcppi1: PC speaker
sysbeep0 at pcppi1
ICH9 (PNP0C01) at acpi0 not configured
acpibut0 at acpi0 (SLPB, PNP0C0E): ACPI Sleep Button
acpibut1 at acpi0 (PWRB, PNP0C0C-170): ACPI Power Button
RMEM (PNP0C01) at acpi0 not configured
ACPI: Enabled 3 GPEs in block 00 to 3F
attimer1: attached to pcppi1
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
pchb0 at pci0 dev 0 function 0: Intel 82G45 Host Bridge (rev. 0x03)
agp0 at pchb0: G4X-family chipset
agp0: detected 32252k stolen memory
agp0: aperture at 0xc0000000, size 0x10000000
ppb0 at pci0 dev 1 function 0: Intel product 2e21 (rev. 0x03)
ppb0: PCI Express capability version 2 <Root Port of PCI-E Root Complex> x16 @ 5.0GT/s
pci1 at ppb0 bus 1
pci1: i/o space, memory space enabled, rd/line, wr/inv ok
i915drmkms0 at pci0 dev 2 function 0: Intel 82G45 Integrated Graphics Device (rev. 0x03)
genfb0 at pci0 dev 2 function 1: Intel product 2e23 (rev. 0x03)
Intel product 2e24 (miscellaneous communications, revision 0x03) at pci0 dev 3 function 0 not configured
wm0 at pci0 dev 25 function 0, 64-bit DMA: 82567V-2 LAN Controller (rev. 0x00)
wm0: interrupting at msi0 vec 0
wm0: PCI-Express bus
wm0: 2048 words FLASH, version 1.8.5
wm0: RX packet buffer size: 10KB
wm0: Ethernet address 00:1c:c0:a1:f5:3a
wm0: 0x2a4080<FLASH,PCIE,ASF_FIRM,AMT,WOL>
makphy0 at wm0 phy 2: Marvell 88E1149 Gigabit PHY, rev. 1
makphy0: 10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
uhci0 at pci0 dev 26 function 0: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci0: interrupting at ioapic0 pin 16
usb0 at uhci0: USB revision 1.0
uhci1 at pci0 dev 26 function 1: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci1: interrupting at ioapic0 pin 21
usb1 at uhci1: USB revision 1.0
uhci2 at pci0 dev 26 function 2: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci2: interrupting at ioapic0 pin 18
usb2 at uhci2: USB revision 1.0
ehci0 at pci0 dev 26 function 7: Intel 82801JI USB EHCI Controller (rev. 0x00)
ehci0: 64-bit DMA
ehci0: interrupting at ioapic0 pin 18
ehci0: BIOS refuses to give up ownership, using force
ehci0: EHCI version 1.0
ehci0: 3 companion controllers, 2 ports each: uhci0 uhci1 uhci2
ehci0: Using DMA subregion for control data structures
usb3 at ehci0: USB revision 2.0
hdaudio0 at pci0 dev 27 function 0: HD Audio Controller
hdaudio0: interrupting at msi1 vec 0
hdaudio0: HDA ver. 1.0, OSS 4, ISS 4, BSS 0, SDO 1, 64-bit
hdafg0 at hdaudio0: Realtek ALC888
hdafg0: DAC00 2ch: Speaker [Jack]
hdafg0: DAC01 2ch: HP Out [Jack]
hdafg0: DIG02 2ch: SPDIF Out [Built-In]
hdafg0: ADC03 2ch: Line In [Jack], Mic In [Jack]
hdafg0: 2ch/2ch 44100Hz 48000Hz 96000Hz 192000Hz PCM16 PCM20 PCM24 AC3
audio0 at hdafg0: playback, capture, full duplex, independent
audio0: slinear_le:16 2ch 48000Hz, blk 1920 bytes (10ms) for playback
audio0: slinear_le:16 2ch 48000Hz, blk 1920 bytes (10ms) for recording
spkr1 at audio0: PC Speaker (synthesized)
wsbell at spkr1 not configured
ppb1 at pci0 dev 28 function 0: Intel 82801JI PCI Express Port (rev. 0x00)
ppb1: PCI Express capability version 1 <Root Port of PCI-E Root Complex> x1 @ 2.5GT/s
pci2 at ppb1 bus 2
pci2: i/o space, memory space enabled, rd/line, wr/inv ok
ppb2 at pci0 dev 28 function 3: Intel 82801JI PCI Express Port (rev. 0x00)
ppb2: PCI Express capability version 1 <Root Port of PCI-E Root Complex> x1 @ 2.5GT/s
pci3 at ppb2 bus 3
pci3: i/o space, memory space enabled, rd/line, wr/inv ok
jmide0 at pci3 dev 0 function 0: JMicron Technology JMB368 PATA Controller (rev. 0x00)
jmide0: 1 PATA port
jmide0: interrupting at ioapic0 pin 19
jmide0: PCI IDE interface used
jmide0: bus-master DMA support present
jmide0: primary channel wired to native-PCI mode
jmide0: primary channel is PATA
atabus0 at jmide0 channel 0
jmide0: secondary channel wired to native-PCI mode
jmide0: secondary channel is unused
uhci3 at pci0 dev 29 function 0: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci3: interrupting at ioapic0 pin 23
usb4 at uhci3: USB revision 1.0
uhci4 at pci0 dev 29 function 1: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci4: interrupting at ioapic0 pin 19
usb5 at uhci4: USB revision 1.0
uhci5 at pci0 dev 29 function 2: Intel 82801JI USB UHCI Controller (rev. 0x00)
uhci5: interrupting at ioapic0 pin 18
usb6 at uhci5: USB revision 1.0
ehci1 at pci0 dev 29 function 7: Intel 82801JI USB EHCI Controller (rev. 0x00)
ehci1: 64-bit DMA
ehci1: interrupting at ioapic0 pin 23
ehci1: BIOS refuses to give up ownership, using force
ehci1: EHCI version 1.0
ehci1: 3 companion controllers, 2 ports each: uhci3 uhci4 uhci5
ehci1: Using DMA subregion for control data structures
usb7 at ehci1: USB revision 2.0
ppb3 at pci0 dev 30 function 0: Intel 82801BA Hub-PCI Bridge (rev. 0x90)
pci4 at ppb3 bus 4
pci4: i/o space, memory space enabled
ahc0 at pci4 dev 0 function 0: Adaptec 2940 Ultra SCSI adapter
ahc0: interrupting at ioapic0 pin 20
ahc0: aic7880: Ultra Wide Channel A, SCSI Id=7, 16/253 SCBs
scsibus0 at ahc0: 16 targets, 8 luns per target
puc0 at pci4 dev 2 function 0: VScom PCI-800 (com, com, com, com, com, com, com, com)
com2 at puc0 port 0 (Generic XT-compatible): ioaddr 0xd180, interrupting at ioapic0 pin 21
com2: ns16550a, 16-byte FIFO
com3 at puc0 port 1 (Generic XT-compatible): ioaddr 0xd188, interrupting at ioapic0 pin 21
com3: ns16550a, 16-byte FIFO
com4 at puc0 port 2 (Generic XT-compatible): ioaddr 0xd190, interrupting at ioapic0 pin 21
com4: ns16550a, 16-byte FIFO
com5 at puc0 port 3 (Generic XT-compatible): ioaddr 0xd198, interrupting at ioapic0 pin 21
com5: ns16550a, 16-byte FIFO
com6 at puc0 port 4 (Generic XT-compatible): ioaddr 0xd1a0, interrupting at ioapic0 pin 21
com6: ns16550a, 16-byte FIFO
com7 at puc0 port 5 (Generic XT-compatible): ioaddr 0xd1a8, interrupting at ioapic0 pin 21
com7: ns16550a, 16-byte FIFO
com8 at puc0 port 6 (Generic XT-compatible): ioaddr 0xd1b0, interrupting at ioapic0 pin 21
com8: ns16550a, 16-byte FIFO
com9 at puc0 port 7 (Generic XT-compatible): ioaddr 0xd1b8, interrupting at ioapic0 pin 21
com9: ns16550a, 16-byte FIFO
fwohci0 at pci4 dev 6 function 0: Lucent Technologies FW322/323 IEEE 1394 Host Controller (rev. 0x70)
fwohci0: interrupting at ioapic0 pin 23
fwohci0: OHCI version 1.0 (ROM=0)
fwohci0: No. of Isochronous channels is 8.
fwohci0: EUI64 00:90:27:00:02:43:ec:9e
fwohci0: Phy 1394a available S400, 2 ports.
fwohci0: Link S400, max_rec 2048 bytes.
ieee1394if0 at fwohci0: IEEE1394 bus
fwip0 at ieee1394if0: IP over IEEE1394
fwohci0: Initiate bus reset
fwohci0: Clear PME# now
ichlpcib0 at pci0 dev 31 function 0: Intel 82801JIB LPC Interface Bridge (rev. 0x00)
timecounter: Timecounter "ichlpcib0" frequency 3579545 Hz quality 1000
ichlpcib0: 24-bit timer
tco0 at ichlpcib0: TCO (watchdog) timer configured.
tco0: Min/Max interval 1/367 seconds
ahcisata0 at pci0 dev 31 function 2: Intel 82801JI SATA Controller (AHCI mode) (rev. 0x00)
ahcisata0: 64-bit DMA
ahcisata0: ignoring broken port multiplier support
ahcisata0: AHCI revision 1.20, 6 ports, 32 slots, CAP 0xe320ffe5<SXS,EMS,CCCS,PSC,SSC,PMD,ISS=0x2=Gen2,SCLO,SAL,SSNTF,SNCQ,S64A>
ahcisata0: interrupting at msi2 vec 0
atabus1 at ahcisata0 channel 0
atabus2 at ahcisata0 channel 1
atabus3 at ahcisata0 channel 2
atabus4 at ahcisata0 channel 3
atabus5 at ahcisata0 channel 4
atabus6 at ahcisata0 channel 5
ichsmb0 at pci0 dev 31 function 3: Intel 82801JI SMBus Controller (rev. 0x00)
ichsmb0: interrupting at ioapic0 pin 18
iic0 at ichsmb0: I2C bus
isa0 at ichlpcib0
pckbc0 at isa0 port 0x60-0x64
acpicpu0 at cpu0: ACPI CPU
acpicpu0: C1: FFH, lat  20 us, pow  1000 mW
coretemp0 at cpu0: thermal sensor, 1 C resolution
coretemp0: autoconfiguration error: WARNING: Tjmax(0) retrieved was below expected range, using default (100).
acpicpu1 at cpu1: ACPI CPU
coretemp1 at cpu1: thermal sensor, 1 C resolution
coretemp1: autoconfiguration error: WARNING: Tjmax(0) retrieved was below expected range, using default (100).
acpicpu2 at cpu2: ACPI CPU
coretemp2 at cpu2: thermal sensor, 1 C resolution
coretemp2: autoconfiguration error: WARNING: Tjmax(0) retrieved was below expected range, using default (100).
acpicpu3 at cpu3: ACPI CPU
coretemp3 at cpu3: thermal sensor, 1 C resolution
coretemp3: autoconfiguration error: WARNING: Tjmax(0) retrieved was below expected range, using default (100).
fwohci0: BUS reset
fwohci0: node_id=0xc800ffc0, gen=1, CYCLEMASTER mode
ieee1394if0: 1 nodes, maxhop <= 0 cable IRM irm(0) (me)
ieee1394if0: bus manager 0
timecounter: Timecounter "clockinterrupt" frequency 100 Hz quality 0
scsibus0: waiting 2 seconds for devices to settle...
IPsec: Initialized Security Association Processing.
uhub0 at usb0: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
uhub1 at usb1: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub1: 2 ports with 2 removable, self powered
uhub2 at usb3: NetBSD (0x0000) EHCI root hub (0x0000), class 9/0, rev 2.00/1.00, addr 1
uhub2: 6 ports with 6 removable, self powered
uhub3 at usb4: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub3: 2 ports with 2 removable, self powered
uhub4 at usb2: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub4: 2 ports with 2 removable, self powered
uhub5 at usb5: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub5: 2 ports with 2 removable, self powered
uhub6 at usb6: NetBSD (0x0000) UHCI root hub (0x0000), class 9/0, rev 1.00/1.00, addr 1
uhub6: 2 ports with 2 removable, self powered
uhub7 at usb7: NetBSD (0x0000) EHCI root hub (0x0000), class 9/0, rev 2.00/1.00, addr 1
uhub7: 6 ports with 6 removable, self powered
ahcisata0 port 0: device present, speed: 3.0Gb/s
ahcisata0 port 1: device present, speed: 3.0Gb/s
uhidev0 at uhub0 port 1 configuration 1 interface 0
uhidev0: DELL (0x413c) DELL USB Keyboard (0x2005), rev 1.10/1.05, addr 2, iclass 3/1
ukbd0 at uhidev0
wskbd0 at ukbd0: console keyboard
atapibus0 at atabus0: 2 targets
cd0 at atapibus0 drive 0: <TOSHIBA DVD-ROM SD-M1612, , 1004> cdrom removable
cd0: 32-bit data port
cd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 2 (Ultra/33)
cd0(jmide0:0:0): using PIO mode 4, Ultra-DMA mode 2 (Ultra/33) (using DMA)
wd0 at atabus1 drive 0
wd0: <ST31500541AS>
wd0: drive supports 16-sector PIO transfers, LBA48 addressing
wd0: 1397 GB, 2907021 cyl, 16 head, 63 sec, 512 bytes/sect x 2930277168 sectors
wd0: GPT GUID: d5ada7dc-44c3-4d82-b024-961966ab7ff7
dk0 at wd0: "efi0", 262144 blocks at 2048, type: msdos
dk1 at wd0: "fe7450b6-6259-4499-b984-54d3e59cc568", 2930012943 blocks at 264192, type: raidframe
wd0: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133), WRITE DMA FUA, NCQ (32 tags)
wd0(ahcisata0:0:0): using PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133) (using DMA), NCQ (31 tags)
wd1 at atabus2 drive 0
wd1: <ST31500541AS>
wd1: drive supports 16-sector PIO transfers, LBA48 addressing
wd1: 1397 GB, 2907021 cyl, 16 head, 63 sec, 512 bytes/sect x 2930277168 sectors
wd1: GPT GUID: 7ea51766-7a2a-4077-8182-f0e8c6e67020
dk2 at wd1: "efi1", 262144 blocks at 2048, type: msdos
dk3 at wd1: "9ae68253-2262-486c-ba52-134ea0fe147f", 2930012943 blocks at 264192, type: raidframe
wd1: drive supports PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133), WRITE DMA FUA, NCQ (32 tags)
wd1(ahcisata0:1:0): using PIO mode 4, DMA mode 2, Ultra-DMA mode 6 (Ultra/133) (using DMA), NCQ (31 tags)
swwdog0: software watchdog initialized
WARNING: findroot: double match for boot device (bootinfo/bootwedge:wd0 bootinfo/bootwedge:wd1)
raid0: RAID Level 1
raid0: Components: /dev/dk1 /dev/dk3
raid0: Total Sectors: 2930012800 (1430670 MB)
raid0: GPT GUID: 0cc7b928-3537-4adc-a337-b90de61d0cb5
dk4 at raid0: "raid0root", 17235968 blocks at 2048, type: ffs
dk5 at raid0: "raid0swap", 50331648 blocks at 17238016, type: swap
dk6 at raid0: "raid0data", 2862443103 blocks at 67569664, type: ffs
WARNING: 4 errors while detecting hardware; check system log.
boot device: dk4
root on dk4 dumps on dk5
root file system type: ffs
kern.module.path=/stand/amd64/11.0/modules
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] Driver supports precise vblank timestamp query.
i915drmkms0: interrupting at ioapic0 pin 16 (i915drmkms0)
[drm] Initialized i915 1.6.0 20200114 for i915drmkms0 on minor 0
intelfb0 at i915drmkms0
[drm] DRM_I915_DEBUG enabled
[drm] DRM_I915_DEBUG_GEM enabled
intelfb0: framebuffer at 0xc0010000, size 1280x1024, depth 32, stride 5120
wsdisplay0 at intelfb0 kbdmux 1: console (default, vt100 emulation), using wskbd0
wsmux1: connecting to wsdisplay0
wsdisplay0: screen 1 added (default, vt100 emulation)
wsdisplay0: screen 2 added (default, vt100 emulation)
wsdisplay0: screen 3 added (default, vt100 emulation)
wsdisplay0: screen 4 added (default, vt100 emulation)


>How-To-Repeat:

>Fix: