RPI5 - 'dmas' DT property is missing or empty, no HDMI audio

[camrossi]

Creating a bug report/issue

• I have searched the existing open and closed issues

Required Information

• DietPi version | cat /boot/dietpi/.version

cat /boot/dietpi/.version
G_DIETPI_VERSION_CORE=10
G_DIETPI_VERSION_SUB=5
G_DIETPI_VERSION_RC=2
G_GITBRANCH='master'
G_GITOWNER='MichaIng'

• Distro version | echo $G_DISTRO_NAME $G_RASPBIAN
trixie 0

• Kernel version | uname -a
Linux rpi5-tv 6.18.34+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.18.34-1+rpt1 (2026-06-09) aarch64 GNU/Linux

• SBC model | echo $G_HW_MODEL_NAME or (EG: RPi3)
  RPi 5 Model B (aarch64)

Steps to reproduce

Connect RPi to HDMI TV, configure it to do Audio over HDMI

Expected behaviour

Audio Over HDMI Works

Actual behaviour

No audio and I get
'dmas' DT property is missing or empty, no HDMI audio

I can fix this by setting: dtparam=audio=on but my understanding is that this parameter is deprecated on RPi5 and the default config anyway sets it to off making HDMI audio broken.

[MichaIng]

dtparam=audio=on enables the Broadcom audio driver snd_bcm2835, which should not be needed or even functional on Raspberry Pi 5. Did you enable HDMI audio via dietpi-config?

When KMS/DRM is enabled, HDMI audio is managed by that stack. aplay -l should show vc4-hdmi audio devices. If it is disabled, snd_bcm2835 manages it instead, which however did not work at all on Raspberry Pi 5 last time I tested. That driver is needed for the analogue 3.5mm audio jack, which is however not present on Raspberry Pi 5, hence the driver is generally not needed there, hence probably not really implemented in the RPi 5 kernel or device tree. For this reason, when enabling HDMI audio in dietpi-config on RPi 5, KMS/DRM and the respective audio stack is enabled automatically.

'dmas' DT property is missing or empty, no HDMI audio

Where exactly do you see this error?

[camrossi]

Hi @MichaIng ,

The 'dmas' DT property is missing or empty, no HDMI audio is show in dmesg

I have set the dtparam=audio=off this is what I see:

root@rpi5-tv:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

root@rpi5-tv:~# dmesg | grep hdmi
[    7.355855] rc rc0: vc4-hdmi-0 as /devices/platform/soc@107c000000/107c701400.hdmi/rc/rc0
[    7.355900] input: vc4-hdmi-0 as /devices/platform/soc@107c000000/107c701400.hdmi/rc/rc0/input1
[    7.356265] vc4_hdmi 107c701400.hdmi: 'dmas' DT property is missing or empty, no HDMI audio

And no Sound.

Now I set the dtparam=audio=on this is what I see:

root@rpi5-tv:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 1: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Noteic the vc4hdmi0 was missing before...

root@rpi5-tv:~# dmesg | grep hdmi
[    7.237075] rc rc0: vc4-hdmi-0 as /devices/platform/soc@107c000000/107c701400.hdmi/rc/rc0
[    7.237114] input: vc4-hdmi-0 as /devices/platform/soc@107c000000/107c701400.hdmi/rc/rc0/input1
[    7.238495] input: vc4-hdmi-0 HDMI Jack as /devices/platform/soc@107c000000/107c701400.hdmi/sound/card0/input2

and now I also get a HDMI Jack...

The only config I have changed is the dtparam=audio=on and without it for some reason the hdmi-0 sound card don't initialise.

[MichaIng]

Do not select the exact vc4hdmi device in dietpi-config, instead select "onboard HDMI" at the top of the list. I know that these are using snd_bcm2835 names is confusing, as it does not always use that driver.

Background is that, when using the KMS/DRM audio stack, the ALSA device requires a certain setup, which is done by /usr/share/alsa/cards/vc4-hdmi.conf, which is loaded only if the default ALSA device remains untouched. When selecting a particular PCM as audio device, it is set as pcm.!default, which means that /usr/share/alsa/cards/vc4-hdmi.conf is not loaded anymore, and essential setup for this to work is missing.

[camrossi]

Yes that is what is actually selected, I was just showing the bottom to show the missing device.

I'm heading to bed now but I can add a screen shot tomorrow 😊

I'll check as well if I have those files

[MichaIng]

and now I also get a HDMI Jack...

But is this really functional on RPi 5, i.e. do you get actual HDMI audio output when selecting the respective vc4hdmi device? Possible that something changed in the kernel a way that it does, but in the past it did not, and dtparam=audio=on did just necessarily invoke the Broadcom driver.

[camrossi]

Not sure I understand the comment 100% :)
My RPi5 is connected to a TV and the only way I can get the audio working over the HDMI0 port (the one closer to the power cable) is by having the dtparam=audio=on

Alsamixer also sees the vc4hdmi card only if dtparam=audio=on as show below

I checked the vc4-hdmi.conf and the content is the same regardless if is on/off, what is probably more interesting is that I did decode the Device tree and indeed the dmas is empty for the HDMI0: left is off right is on
I used the dtc -I fs -O dts /sys/firmware/devicetree/base/ command:

Oddly however is not empty for HDMI1...

It might be something wrong with the kernel I have to admit I am not too sure :)