Updated Bug Report: Intel Comet Lake + Conexant CX20585 (Audio Lock-Up
Resolution)
Hardware: Intel Comet Lake PCH-LP cAVS Codec: Conexant CX20585 (detected via
/proc/asound) Kernel Issue: snd_hda_intel fails to probe codecs on boot; module
unloading is impossible due to persistent dependency lock.
1. Findings & Root Cause
The snd_hda_intel driver fails to initialize the Conexant codec ("Cannot
probe codecs") due to a strict dependency lock created by the HDMI audio
stack.
The Lock: The module snd_hda_codec_intelhdmi holds a reference to
snd_hda_codec_hdmi, which in turn locks the audio controller.
The Failure: This lock persists even when trying to manually unload
modules (modprobe -r), resulting in FATAL: Module is in use errors. This
prevents the necessary hardware reset from occurring.
Impact: The system boots into a "Dummy Output" state because the
controller is effectively zombie-locked by the HDMI driver before the
analog codec can be probed.
2. Successful Workaround (The "HDMI Blacklist" Method)
A stable, persistent fix was achieved only by preventing the HDMI audio
stack from loading entirely. Standard kernel parameters (i915.audio=0,
probe_mask) were insufficient to break the lock.
Configuration:
Blacklist HDMI Audio:
blacklist snd_hda_codec_hdmi
blacklist snd_hda_codec_intelhdmi
Result: Prevents the dependency chain from forming, allowing the
main driver to be unloaded/reloaded.
Runtime "Jailbreak" Service: A systemd service executes a PCI reset
script 15 seconds post-boot:
Unload: modprobe -r snd_hda_intel (Successful only because HDMI
is blacklisted).
PCI Reset: echo 1 > /sys/bus/pci/devices/0000:00:1f.3/remove
then rescan.
Reload: modprobe snd_hda_intel model=auto position_fix=4
power_save=0
3. Critical Parameters for this Chipset
Once the lock was broken, the following parameters were required for
stability:
model=auto: Required for Conexant CX20585 Headphone Jack detection
(generic failed to switch outputs).
position_fix=4 (POSIX_FIX_POSBUF): Required to eliminate severe
audio crackling/static.
power_save=0: Required to prevent "popping" and device loss on
suspend/resume.
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https://bugs.launchpad.net/bugs/2130757
Title:
Comet Lake PCH-LP cAVS: Analog audio (Realtek ALCxxx) not detected,
only HDMI outputs present (Dummy Output issue).
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