Is it possible to disable VC4 sound?

[vanfanel]

Hi,

Using the BRCM drivers, there's the "dtparam=audio=off" option in config.txt to disable loading the audio modules, but what's the way to do the same with the VC4 drivers?
I am having problems with my HifiBerry DAC+ and I would like to disable the onboard audio.
I suppose I could build a kernel without VC4 audio support, but I'm sure there must be a way to archieve the same without rebuilding the kernel, right?

Thanks

[JamesH65]

@popcornmix @pelwell Not quite sure what is wanted here. Is there such a thing as VC4 audio support? Nothing in the kernel config about it.

@vanfanel What do you mean by VC4 audio with regard to the Linux kernel?

[JamesH65]

@popcornmix Any ideas?

[JamesH65]

The audio driver is bcm2835-audio, it's a module, so can you simply remove the module to disable it?

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[pelwell]

I'm pretty sure he's referring to the HDMI audio support available from the VC4 driver, but why he couldn't reply to that effect beats me.

Audio is part of the regular vc4_hdmi driver, which is itself bundled into the overall vc4 module, so blacklisting won't work. It will skip the audio initialisation without failing to create everything else if the Device Tree node has no dmas property, but deleting a property isn't possible with an overlay. Fortunately a present-but-empty dmas doesn't make any sense, so we can modify the driver to treat an empty dmas the same as an absent one.

If @vanfanel shows an interest I can make that change and add an overlay parameter to control it, otherwise I have more important things to do.

[vanfanel]

@JamesH65 and @pelwell : I am VERY sorry I did nor reply earlier. I thought I had! Sorry.

I am referring to the VC4-related vc4-hdmi ALSA card, yes, not the bcm2835 ALSA card. The bcm2835 card works fine, and I know it can be disabled on config.txt very easily.
But the vc4-hdmi audio card provided by the VC4 stack only seems to support one format and frequency:

#3043

So, yes, disabling the vc4-hdmi in config.txt card via an overlay parameter would be desirable.
But even better would be having the vc4-hdmi audio card working instead of depending on the (deprecated?) bmc2835 interface.

[pelwell]

Tweaking the driver and adding the overlay parameter is something I can do in a few minutes, getting the driver to work could take days/weeks for me.

[vanfanel]

@pelwell: I perfectly understand.
Do you have an idea on why the vc4-hdmi driver only supports one audio format? Is it still being developed?

[pelwell]

Is it still being developed?

Yes and no - it isn't finished (in that it isn't fully featured), but the developer isn't actively working on it.

[vanfanel]

@pelwell : This is shocking! The vc4 development is abandoned? What will be the graphics standard for the Pi then?

[pelwell]

Others are being moved onto the project, but progress will be slow for a while.

[popcornmix]

Note: you can still use the legacy alsa driver with vc4-fkms-v3d (and vc4-kms-v3d).
That is how LibreELEC is configured on Pi4.

[vanfanel]

@popcornmix : full vc4-kms-v3d is what I use on my projects involving small Pi systems. I know the legacy alsa driver (bmc2835) works fine with that, but having two ALSA drivers (legacy bmc2835 and vc4-hdmi) is causing problems, thats why I was asking if the non-working vc4-hdmi alsa driver could be somehow disabled.

[pelwell]

I'll add the ability to disable it when I get a spare moment.

[vanfanel]

@pelwell : Thanks!

[pelwell]

I've pushed patches that should resolve this issue for you. They'll get picked up by future kernel builds.

[vanfanel]

@pelwell: Great! I hope one day we can rely on the vc4-hdmi ALSA driver... but for now, this will do!

[6by9]

The hardware only supports one format, and that is SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_LE.
Questions were asked on the relevant kernel mailing lists as to who or what should be responsible
for adding that encapsulation when the client wants to provide something else, but no answers were forthcoming.

Duplication in all relevant drivers seems wrong and alsa should in theory support it, but getting the magic runes in asoundrc correct is non-trivial. There is some reference in https://anholt.livejournal.com/49474.html?nojs=1, but I can't find the kernel mailing list references at present.
Memory says Pulseaudio will also deal with it all for you, and allows mixing of the streams prior to encapsulation which AIUI alsalib won't allow you to do.

[popcornmix]

@vanfanel this is in latest rpi-update kernel. Can you test? I think you want:

dtoverlay=vc4-kms-v3d,audio=off

[vanfanel]

@popcornmix : Yes! It works! 👍

@6by9 : I put all the information I could find regarding a possible asoundrc here: #3043
There is a supposedly working asoundrc in: https://github.com/raw/takaswie/alsa-lib/master/src/conf/cards/vc4-hdmi.conf
...but sadly it does not work for me.
As you can see, I tried different combinations with no success... I believe ALSA can take care of format conversions.

[DennisFury]

just wanted to say I also ran into this issue. Mine was a bit different, my USB speaker and one of the HDMI audios (vc4hdmi#) kept switching positions as the card # (result of aplay -l ) after each reboot. I use this as a personal kisok display and my script would fail to run after 1/2 the reboots because no audio device found (wrong default device set).

Using this command in /boot/config.txt and now I only see 1 HDMI audio in aplay -l
dtoverlay=vc4-kms-v3d,audio=off

so far so good, I would expect both HDMI audio devices to be gone ( I still see vc4hdmi1, but at least vc4hdmi0 is gone).

4 reboots and he card numbers for the devices appear to be sticking.

thanks

[uxigene]

just wanted to say I also ran into this issue. Mine was a bit different, my USB speaker and one of the HDMI audios (vc4hdmi#) kept switching positions as the card # (result of aplay -l ) after each reboot. I use this as a personal kisok display and my script would fail to run after 1/2 the reboots because no audio device found (wrong default device set).

Using this command in /boot/config.txt and now I only see 1 HDMI audio in aplay -l dtoverlay=vc4-kms-v3d,audio=off

so far so good, I would expect both HDMI audio devices to be gone ( I still see vc4hdmi1, but at least vc4hdmi0 is gone).

4 reboots and he card numbers for the devices appear to be sticking.

thanks

Have same issue. Can't disable vc4hdmi1 in my rasberrypi 4

[strilov]

Hi. In case this is still an issue, there seems to be a pi4 specific overlay, which has audio options for hdmi0 and hdmi1: https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/vc4-kms-v3d-pi4-overlay.dts#L181

[mightyoakbob]

Interesting, thanks for the info, just wish i understood it.
Bob.

[vanfanel]

Hi. In case this is still an issue, there seems to be a pi4 specific overlay, which has audio options for hdmi0 and hdmi1: https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/vc4-kms-v3d-pi4-overlay.dts#L181

Can you please give an example on how to use that overlay to get video & audio on HDMI-1 only?

Thanks

[pelwell]

There is help available: $ dtoverlay -h vc4-kms-v3d (or browse the README directly).
The answer you are looking for is:

dtoverlay=vc4-kms-v3d,nohdmi0

Unless you are labelling the connectors 1 & 2, in which case you want:

dtoverlay=vc4-kms-v3d,nohdmi1

[vanfanel]

There is help available: $ dtoverlay -h vc4-kms-v3d (or browse the README directly). The answer you are looking for is:

dtoverlay=vc4-kms-v3d,nohdmi0

Unless you are labelling the connectors 1 & 2, in which case you want:

dtoverlay=vc4-kms-v3d,nohdmi1

Ah, yes, thanks for that :)