vc4.ko brings unusable&unstable ALSA sinks

[Ryutaroh Matsumoto]

Hi all,

This is again an issue regarding on vc4.ko.
This is observed both on the plain upstream kernel 5.10.24 and
the latest Raspberry Pi OS kernel 5.10.17.

With vc4.ko, ALSA devices vc4-hdmi-[01] are brought as the bottom of this email.
aplay /usr/share/sounds/alsa/Front_Center.wav -D sysdefault:CARD=vc4hdmi[01]
gives no effect/sound (even on Raspberry Pi OS).
In addition, touching vc-hdmi-[01] ALSA devices cause lots of kernel error messages

bcm2835_audio bcm2835_audio: vchi message timeout
vc4_hdmi fef05700.hdmi: ASoC: error at snd_soc_dai_startup on fef05700.hdmi: -19

Touching vc4-hdmi-[01] too many times makes the kernel unstable,
and shutting down often needs several minutes.

/usr/bin/pulseaudio in its default setting touches all available  ALSA sinks
and causes the above inconvenience.

I mainly use HDMI audio output, and 

plughw:CARD=ALSA,DEV=1
    bcm2835 ALSA, bcm2835 IEC958/HDMI
    Hardware device with all software conversions

is sufficient for my audio playing. For pulseaudio, I am using
load-module module-alsa-sink device=hw:2,1
and commenting out
#load-module module-udev-detect
#load-module module-detect

I wonder if what is intended use of vc4-hdmi-[01] ALSA sinks,
which seems only bringing inconvenience and unstability...

The Debian package versions are as follows:
# dpkg-query -W | egrep linux-image\|firmware
bluez-firmware	1.2-4
firmware-brcm80211	20210315-1
firmware-linux-free	20200122-1
firmware-misc-nonfree	20210315-1
linux-image-5.10.0-5-rt-arm64	5.10.24-1
linux-image-rt-arm64	5.10.24-1
raspi-firmware	1.20210111+ds-2


# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM vc4-hdmi-hifi-0 [MAI PCM vc4-hdmi-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM vc4-hdmi-hifi-0 [MAI PCM vc4-hdmi-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 7/7
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
card 2: ALSA [bcm2835 ALSA], device 1: bcm2835 IEC958/HDMI [bcm2835 IEC958/HDMI]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

# aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
default
    Default Audio Device
sysdefault
    Default Audio Device
iec958
    IEC958 (S/PDIF) Digital Audio Output
lavrate
    Rate Converter Plugin Using Libav/FFmpeg Library
samplerate
    Rate Converter Plugin Using Samplerate Library
speexrate
    Rate Converter Plugin Using Speex Resampler
jack
    JACK Audio Connection Kit
oss
    Open Sound System
pulse
    PulseAudio Sound Server
upmix
    Plugin for channel upmix (4,6,8)
vdownmix
    Plugin for channel downmix (stereo) with a simple spacialization
hw:CARD=vc4hdmi0,DEV=0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Direct hardware device without any conversions
plughw:CARD=vc4hdmi0,DEV=0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Hardware device with all software conversions
default:CARD=vc4hdmi0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Default Audio Device
sysdefault:CARD=vc4hdmi0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Default Audio Device
front:CARD=vc4hdmi0,DEV=0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Front output / input
iec958:CARD=vc4hdmi0,DEV=0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=vc4hdmi0,DEV=0
    vc4-hdmi-0, MAI PCM vc4-hdmi-hifi-0
    Direct sample mixing device
usbstream:CARD=vc4hdmi0
    vc4-hdmi-0
    USB Stream Output
hw:CARD=vc4hdmi1,DEV=0
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Direct hardware device without any conversions
plughw:CARD=vc4hdmi1,DEV=0
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Hardware device with all software conversions
default:CARD=vc4hdmi1
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Default Audio Device
sysdefault:CARD=vc4hdmi1
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Default Audio Device
front:CARD=vc4hdmi1,DEV=0
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Front output / input
iec958:CARD=vc4hdmi1,DEV=0
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    IEC958 (S/PDIF) Digital Audio Output
dmix:CARD=vc4hdmi1,DEV=0
    vc4-hdmi-1, MAI PCM vc4-hdmi-hifi-0
    Direct sample mixing device
usbstream:CARD=vc4hdmi1
    vc4-hdmi-1
    USB Stream Output
hw:CARD=ALSA,DEV=0
    bcm2835 ALSA, bcm2835 ALSA
    Direct hardware device without any conversions
hw:CARD=ALSA,DEV=1
    bcm2835 ALSA, bcm2835 IEC958/HDMI
    Direct hardware device without any conversions
plughw:CARD=ALSA,DEV=0
    bcm2835 ALSA, bcm2835 ALSA
    Hardware device with all software conversions
plughw:CARD=ALSA,DEV=1
    bcm2835 ALSA, bcm2835 IEC958/HDMI
    Hardware device with all software conversions
default:CARD=ALSA
    bcm2835 ALSA, bcm2835 ALSA
    Default Audio Device
sysdefault:CARD=ALSA
    bcm2835 ALSA, bcm2835 ALSA
    Default Audio Device
dmix:CARD=ALSA,DEV=0
    bcm2835 ALSA, bcm2835 ALSA
    Direct sample mixing device
dmix:CARD=ALSA,DEV=1
    bcm2835 ALSA, bcm2835 IEC958/HDMI
    Direct sample mixing device
usbstream:CARD=ALSA
    bcm2835 ALSA
    USB Stream Output

Best regards, Ryutaroh Matsumoto