vc4.ko brings unusable&unstable ALSA sinks

[Ryutaroh Matsumoto]

Hi Dave, thank you for your email.

> snd_bcm2835 has two modes of operation, controlled by module parameters.
> enable_compat_alsa=1 will expose one audio device that can be switched
> between analogue out and HDMI via a control. This is generally not
> used now.
> enable_compat_alsa=0 will create separate devices for each output.
> enable_headphones and enable_hdmi control which devices should be
> enabled. Do not use enable_hdmi=1 if using the vc4 DRM/KMS driver.

One of problems in the upstream snd_bcm2835.ko (not including Raspberry Pi OS)
is that it does not honor the module parameters. For example,
enable_compat_alsa=0/1 enable_hdmi=0
does not prevent snd_bcm2835.ko from touching HDMI audio.

This was reported to the upstream maintainers as
http://lists.infradead.org/pipermail/linux-rpi-kernel/2021-March/008082.html

Best regards, Ryutaroh