Bug Report: iMac 18,3 – CS8409/CS42L83 Audio Chip Not Functional on Linux Introduction This report documents an in-depth technical analysis of audio failure on the iMac 18,3 (27" 5K, 2017), which uses the Cirrus Logic CS8409/CS42L83 audio chipset. The issue was reproduced across multiple distributions and environments:
Zorin OS 17.3 with Wayland Fedora OS 42 with GNOME and Wayland Both systems exhibited identical failures in ALSA’s parser and kernel- level audio initialization. The root cause spans three layers of the system: the kernel driver, ALSA/UCM configuration, and distribution- level integration. Overview of the Original Problems # Problem Technical Detail Consequence 1 Faulty kernel driver The standard snd_hda_intel module loads but lacks Apple’s proprietary verb sequence required to wake the DSP and activate the amplifier Hardware remains inactive, controls are not exposed 2 UCM profile blocked ALSA’s parser reads the UCM profile, which expects specific controls (e.g., Bass Speaker PEQ), but rejects it because the inactive hardware doesn’t expose them The sound routing chain fails to initialize 3 Failed automatic installation The original installation script failed to compile and deploy the module and profile Both the driver and UCM profile remained non-functional Solution We Applied Action Problem Solved Result Installed patched module snd-hda-codec-cs8409 (egorenar’s version) Problem 1 The module includes the missing initialization code, activates the hardware, and exposes all required controls Manually created UCM profile with PEQ filters Problem 2 The profile loads successfully, the parser accepts it, and the sound routing chain is activated Final system reboot Problem 3 The system boots with the patched module and functional UCM profile, resulting in stable and persistent audio output Diagnostic Outputs (available upon request) Output of dmesg | grep cs8409 Output of aplay -l Output of alsaucm -c HDA-Intel-PCH get _devices Contents of imac_pincfgs[] from the patched driver source Custom UCM2 profile HiFi.conf with PEQ definitions I am also attaching an installer script named iMac_CS8409_Installer.sh — simply run it, and the module and UCM profile will be installed automatically Recommendations for Ubuntu/ALSA Include the snd-hda-codec-cs8409 module in the linux-modules-extra package Add documentation for Apple iMac 18,x models using the CS42L83 audio chipset Consider patching alsa-lib to support Syntax 4 and PEQ control definitions ** Attachment added: "iMac_CS8409_Fix.zip" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2119402/+attachment/5915151/+files/iMac_CS8409_Fix.zip -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2119402 Title: )Persistent driver issues on iMac 18,3 (27", 2017) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2119402/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
