snd-hda-codec-cs8409 (out-of-tree)

Out-of-tree Linux kernel module for the Cirrus Logic CS8409 HD Audio bridge and related fixups (including Apple machine quirks). It mirrors the in-kernel ALSA HDA codec driver logic but can be built and updated without rebuilding the whole kernel.

Requirements

Linux kernel headers for the kernel you are running
(e.g. on Debian/Ubuntu/Pop!_OS: linux-headers-$(uname -r))
Toolchain able to build external modules (gcc, make, etc.)
Build from a shell where uname -r matches the target kernel (or set KVER — see below)

Build

Always build from this directory using the provided Makefile so module C flags are applied correctly:

cd /path/to/snd-hda-codec-cs8409
make

Do not run only:

make -C /lib/modules/$(uname -r)/build M=$(pwd) modules

without passing the same CFLAGS_MODULE values as in the Makefile all: recipe. The Makefile sets defines such as APPLE_CODECS and CONFIG_SND_HDA_RECONFIG that this tree expects.

Optional: build for another installed kernel

make KVER=6.18.7-76061807-generic

(Use the directory name under /lib/modules/ for that kernel.)

Install module into `updates/` (takes precedence over in-tree module)

sudo make install
sudo depmod -a   # install target runs depmod; repeat if you copy the .ko manually

Reload the audio stack or reboot as appropriate on your distribution (e.g. unload/reload snd-hda-intel and related modules, or reboot).

Kernel compatibility

Recent work in this repository targets modern kernels (6.17+) where the ALSA HDA stack uses:

struct hda_codec_driver with probe / remove instead of the old codec->patch_ops / .free callbacks
snd_hda_gen_remove() instead of the former snd_hda_gen_free() export (a compatibility wrapper in hda_generic.h maps the old name for this module)

The module has been verified to build and run on 6.18.x (e.g. Pop!_OS). Older kernels may still work if the symbols and APIs match; if not, use a branch or commit intended for that era.

Tested on

Environment	Kernel	Notes
Pop!_OS	`6.18.7-76061807-generic`	`make` and `sudo make install` succeed; audio confirmed working after reload/reboot as needed on the test machine.

Always install kernel headers that match your running kernel (linux-headers-$(uname -r) on Debian-based systems).

Development

The entire set of changes in this repository as published here—the kernel 6.17+ HDA API port (hda_codec_driver, variant ops, snd_hda_gen_remove compatibility), Makefile / .gitignore updates, README, and related integration—was written and iterated using Cursor (AI-assisted editor). The CS8409 codec logic and Apple extensions remain derived from Cirrus Logic and the Linux ALSA HDA codebase; original SPDX and copyright lines in the source files still apply.

Configuration flags (Makefile)

KBUILD_EXTRA_CFLAGS enables, among other things:

APPLE_CODECS — Apple-specific paths in patch_cirrus_apple.h
APPLE_PINSENSE_FIXUP
CONFIG_SND_HDA_RECONFIG

A debug-oriented line is commented out in the Makefile (extra logging defines).

License

The sources are under GPL-2.0-or-later (see SPDX headers in the individual files). This tree includes code attributed to Cirrus Logic and Takashi Iwai / the ALSA project, consistent with the upstream HDA codec drivers.

Troubleshooting

Issue	What to check
`No rule to make target .../build`	Install kernel headers for `uname -r`.
Many errors about missing `cs8409_spec` fields	Build with this repo’s `make` (see above), not bare kbuild without `CFLAGS_MODULE`.
`modpost: "snd_hda_gen_free" undefined`	Use a tree that includes the `hda_generic.h` wrapper for `snd_hda_gen_remove` (kernel ≥ 6.17).
Compiler differs from kernel	Usually a warning only; same major `gcc` as the distro kernel is ideal.

Contributing

Pull requests and reports against specific kernel version and hardware (PCI subsystem ID, machine model) help keep this module useful for others.

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