External monitor is missing from the display output list in GNOME Settings after connecting HDMI following a cold boot

[zjzhao-eda]

snap_list.log
dmesg-of-boot-3ac4985b9a7d4eabbe418879cd7f6f67.log

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name: Bug report
about: External monitor is missing from the display output list in GNOME Settings after connecting HDMI following a cold boot

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[Summary]
While connecting an external HDMI monitor to DUT via HDMI cable, I cannot select the sink option of HDMI monitor in Gnome Settings

[Steps to Reproduce]

1. Flash image and poweroff DUT
2. Cold boot DUT without an external monitor
3. Open Gnome Settings and navigate to Sounds section
4. Check if there's a sink option of the external Monitor

[Expected Result]
Able to choose the sink option of HDMI monitor

[Actual Result]

1. Able to play the sound via HDMI monitor by the following command

$ aplay -D plughw:CARD=vc4hdmi0,DEV=0 /usr/share/sounds/alsa/Front_Right.wav

2.Only the following sink options be listed in Gnome Settings (w/o plugging headset, w/ an external HDMI monitor)

Speakers - USB Advanced Audio Device

Digital Ouptut (S/PDIF) - USB Advanced Audio Device

When issue happens, hotplug the external monitor doesn’t work

GPU:
System Product Name:
Bios Version:
Kernel Version: 7.0.0-1012-raspi

[Stage]
Right after it happened

[popcornmix]

Gnome settings are not something we modify or support. You may be better off asking this question in a forum relevant to your OS (Ubuntu?)

If you see the same behaviour on RPiOS trixie with default settings, then we can investigate further.

[zjzhao-eda]

HDMI audio device not detected on hot-plug when booting without an HDMI display (Raspberry Pi OS Trixie / CM5)

I believe I have reproduced this issue on Raspberry Pi OS Trixie, and it appears to be the same problem previously observed on Ubuntu OS.

Environment:

Hardware: Raspberry Pi Compute Module 5 (CM5)

OS: Raspberry Pi OS Trixie (latest image)

Kernel: 6.18.34+rpt-rpi-2712

Steps to reproduce:

Boot the CM5 with an HDMI display (with audio support) already connected.

Observed: HDMI audio options appear in the sound/volume settings and work correctly.

Boot the CM5 with no HDMI display connected.

Observed: HDMI audio options are absent, which is expected.

Hot-plug the same HDMI display after the system has fully booted.

Observed: The HDMI audio options still do not appear, even though the display itself is detected.

Reboot the device with the display connected.

Observed: The HDMI audio options return.

Expected behavior:
After hot-plugging an HDMI display that supports audio, the HDMI audio device should be detected and made available in the sound settings without requiring a reboot.

Actual behavior:
HDMI audio is never detected during a hot-plug event. It only becomes available if the HDMI display is connected at initial power-on.

Additional notes:
I took some screenshots but the upload seems to have failed. I can re-upload them if needed. Please let me know if you require any further information or specific tests — I am happy to help.

[6by9]

The kernel creates the relevant hotplug events through the audio subsystem to report connection/disconnection of the audio device through
snd_soc_jack_report(jack, hcp->jack_status, SND_JACK_AVOUT); and documented in https://docs.kernel.org/6.18/sound/soc/jack.html

That gets reported as a boolean mixer control "HDMI Jack".
eg

pi@raspberrypi:~ $ amixer contents
numid=1,iface=CARD,name='HDMI Jack'
  ; type=BOOLEAN,access=r-------,values=1
  : values=on
numid=6,iface=MIXER,name='PCM Playback Volume'
  ; type=INTEGER,access=rw---RW-,values=2,min=0,max=255,step=0
  : values=255,255
  | dBscale-min=-51.00dB,step=0.20dB,mute=0
numid=5,iface=PCM,name='ELD'
  ; type=BYTES,access=r--v----,values=128
  : values=0x10,0x00,0x08,0x00,0x6b,0x10,0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x10,0xac,0xea,0xa0,0x44,0x45,0x4c,0x4c,0x20,0x55,0x32,0x37,0x31,0x38,0x51,0x09,0x1f,0x07,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
numid=4,iface=PCM,name='IEC958 Playback Default'
  ; type=IEC958,access=rw------,values=1
  : values=[AES0=0x04 AES1=0x82 AES2=0x00 AES3=0x02]
numid=3,iface=PCM,name='IEC958 Playback Mask'
  ; type=IEC958,access=r-------,values=1
  : values=[AES0=0xff AES1=0xff AES2=0xff AES3=0xff]
numid=2,iface=PCM,name='Playback Channel Map'
  ; type=INTEGER,access=r--v-R--,values=8,min=0,max=36,step=0
  : values=0,0,0,0,0,0,0,0
  | container
    | chmap-fixed=FL,FR

Unplug HDMI and that first control changes to off

pi@raspberrypi:~ $ amixer contents
numid=1,iface=CARD,name='HDMI Jack'
  ; type=BOOLEAN,access=r-------,values=1
  : values=off

It also gets reported via the input subsystem, so evtest for device vc4-hdmi-0 HDMI Jack reports

pi@raspberrypi:~ $ evtest
No device specified, trying to scan all of /dev/input/event*
Not running as root, no devices may be available.
Available devices:
/dev/input/event0:	Dell KB216 Wired Keyboard
/dev/input/event1:	Dell KB216 Wired Keyboard System Control
/dev/input/event2:	Dell KB216 Wired Keyboard Consumer Control
/dev/input/event3:	Logitech USB Optical Mouse
/dev/input/event4:	pwr_button
/dev/input/event5:	vc4-hdmi-0
/dev/input/event6:	vc4-hdmi-0 HDMI Jack
/dev/input/event7:	vc4-hdmi-1
/dev/input/event8:	vc4-hdmi-1 HDMI Jack
Select the device event number [0-8]: 6
Input driver version is 1.0.1
Input device ID: bus 0x0 vendor 0x0 product 0x0 version 0x0
Input device name: "vc4-hdmi-0 HDMI Jack"
Supported events:
  Event type 0 (EV_SYN)
  Event type 5 (EV_SW)
    Event code 6 (SW_LINEOUT_INSERT) state 1
Properties:
Testing ... (interrupt to exit)
Event: time 1782746012.326677, type 5 (EV_SW), code 6 (SW_LINEOUT_INSERT), value 0
Event: time 1782746012.326677, -------------- SYN_REPORT ------------
Event: time 1782746016.410031, type 5 (EV_SW), code 6 (SW_LINEOUT_INSERT), value 1
Event: time 1782746016.410031, -------------- SYN_REPORT ------------

value 0 is disconnect, and value 1 on connect.

That behaviour is consistent whether the HDMI display was connected or not at reboot.

Pipewire on Raspberry Pi OS listens to the relevant events updates the state appropriately.

[zjzhao-eda]

I followed your steps and tested it, confirming that the issue lies with Pipewire, not the kernel driver.

Our engineer colleague modified the vc4_hdmi.c file in the GPU driver and created a patch file as linked below:

0001-drm-vc4-hdmi-Allow-audio-PCM-open-prepare-without-a-.patch

This patch allows the ALSA PCM audio device to be opened and prepared normally even without an HDMI display connected. In actual testing, it has achieved very good results.

However, since we are not very familiar with graphics, we are unsure whether this is a good solution. We hope you could give us some advice. Thanks.

Meanwhile, I will reach out to the Pipewire project and submit this issue to see if there is a better solution.