[pulseaudio-discuss] Linux Mint 20.1: the internal mic of ALC255 card is not recognised sometimes on reboot

[Vikas Rawal]

I have a Linux Mint 20.1 (kernel 5.8.0-53) installation on my laptop. The
system also has kernel 5.4.0-73, but the problem is not dependent on the
choice between these two. The sound card of my laptop (which looks like a
generic intel card) is behaving strangely. Sometimes on reboot, the
internal mic stops working.

When the mic is working, the output of "pacmd list-sources" shows that
there are two sources:
index: 0
name: <alsa_output.pci-0000_00_1f.3.analog-stereo.monitor>

* index: 1
name: <alsa_input.pci-0000_00_1f.3.analog-stereo>

The full output is here: https://pastebin.com/DHH2CzC7

index 1 shows that there are two ports: analog-input-internal-mic and
analog-input-mic. Analog-input-internal-mic is the inbuilt microphone,
while the analog-input-mic is connected to the 3.5mm jack (and connects to
the microphone of the headset). When I plugin the headset, the active port
becomes <analog-input-mic>.

----
ports:
analog-input-internal-mic: Internal Microphone (priority 8900, latency
offset 0 usec, available: unknown)
properties:
device.icon_name = "audio-input-microphone"
analog-input-mic: Microphone (priority 8700, latency offset 0 usec,
available: no)
properties:
device.icon_name = "audio-input-microphone"
active port: <analog-input-internal-mic>
----

Sometimes on reboot, the internal mic simply vanishes. Now, the pacmd shows
only one source (alsa_output .. monitor):
index: 0
name: <alsa_output.pci-0000_00_1f.3.analog-stereo.monitor>

See the output here: https://pastebin.com/BawabVZh

index 1, alsa_input....., does not show up at all.

If I plugin the headset, a new input index (numbered 2) shows up, with only
one port <analog-input-mic>, which connects to the microphone of the
headset.

How is it that the internal source is sometimes detected and sometimes not?
It is really random. On some reboots it works and on some it doesn't.

It would be really helpful if somebody could point out what might be going
wrong? Or, point in the direction where the problem/solution may lie? How
does one debug something like this?

Thanks in advance,

Vikas
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