Document neon audio fixes (avs driver, topologies, cros UCM)
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Claude Opus 5.5
Claude Opus 5.5
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# Audio on hp-chell (KDE neon)
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Working state (verified 2026-09-27): speakers, headset jack and internal
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mic work under neon. PipeWire/WirePlumber shows `Built-in Audio Speaker`
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and `Built-in Audio Internal Microphone`, and the headset appears when
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something is plugged in. None of this works out of the box. It took the
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fixes below, all applied **2026-03-05**, reconstructed on 2026-09-27
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from `~/.bash_history` and file timestamps.
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## Hardware
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HP Chromebook 13 G1 ("chell", Skylake). The audio DSP is Intel Skylake
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SST, driven by the kernel's **`avs`** driver (`snd_soc_avs`), with three
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board-specific machine drivers. Each one is its own ALSA card:
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| Card | Driver | What |
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|---|---|---|
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| `avs_ssm4567` | `snd_soc_avs_ssm4567` | speakers: 2x ADI SSM4567 amps |
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| `avs_nau8825` | `snd_soc_avs_nau8825` | headset jack: Nuvoton NAU88L25 codec |
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| `avs_dmic` | `snd_soc_avs_dmic` | internal digital mic |
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| `avs_probe_mb` | `snd_soc_avs_probe` | DSP debug probe, not a real device |
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The cards report the long name `Google-Chell-1.0`.
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Speaker safety: the upstream script disables speakers on Chromebooks
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with a **MAX98357A** amp (no volume limiter, so it can blow the
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speakers). Chell uses **SSM4567**, not MAX98357A, so that doesn't apply
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and the speakers are enabled.
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## The fixes
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### 1. WeirdTreeThing's `chromebook-linux-audio` script
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Checkout: `~/github/chromebook-linux-audio`
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(<https://github.com/WeirdTreeThing/chromebook-linux-audio>, shallow
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clone at `8c7e15e`, 2026-02-16). Run as `sudo ./setup-audio -b chell`.
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`-b` is the branch of the UCM repo to clone, and there's no `chell`
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branch; a plain `./setup-audio` is what's intended. For a Skylake board
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(`skl`/`kbl`/`apl`) it:
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- **Switches the DSP driver to `avs`**:
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`/etc/modprobe.d/snd-avs.conf`
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```
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options snd-intel-dspcfg dsp_driver=4
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options snd-soc-avs ignore_fw_version=1
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options snd-soc-avs obsolete_card_names=1
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```
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`dsp_driver=4` selects `avs`. Without it `snd-intel-dspcfg` picks
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legacy HDA or SOF, and neither works on chell. `obsolete_card_names=1`
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gives the `avs_ssm4567`-style card names that the UCM profiles below
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match on.
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- **Installs Chromebook UCM profiles**: clones
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<https://github.com/WeirdTreeThing/alsa-ucm-conf-cros> and copies
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`ucm2/` into `/usr/share/alsa/ucm2/`, and `overrides/` into
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`/usr/share/alsa/ucm2/conf.d/`. The ones this board uses are
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`conf.d/avs_ssm4567/`, `conf.d/avs_nau8825/` and `conf.d/avs_dmic/`
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(`avs_ssm4567/HiFi.conf` sets amp boost, the master volumes at 219,
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and `Left/Right Speaker Switch`).
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- **Adds WirePlumber headroom**:
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`/etc/wireplumber/wireplumber.conf.d/51-increase-headroom.conf` sets
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`api.alsa.headroom = 2048` on all `alsa_output.*` nodes (the script
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says it fixes instability and crashes on these DSPs).
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- Runs `alsactl init`.
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### 2. Duplicate modprobe option (harmless)
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`/etc/modprobe.d/inteldsp.conf`: `options snd-intel-dspcfg dsp_driver=4`,
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written by hand a few minutes before the script ran. It duplicates the
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first line of `snd-avs.conf`. You can delete it.
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### 3. AVS topology files, downloaded by hand
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The `avs` driver needs a per-board **topology** blob for each machine
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driver. Ubuntu's `linux-firmware-intel-misc` ships only the base DSP
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firmware (`/lib/firmware/intel/avs/skl/dsp_basefw.bin.zst` plus one
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module), not the topologies, and the script doesn't provide them
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either. They were fetched straight from upstream linux-firmware:
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```
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cd /lib/firmware/intel/avs/
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BASE=https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/avs
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sudo wget $BASE/ssm4567-tplg.bin $BASE/nau8825-tplg.bin $BASE/dmic-tplg.bin
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```
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Installed: `ssm4567-tplg.bin`, `nau8825-tplg.bin` and `dmic-tplg.bin`
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(not owned by any package, so apt won't update or remove them). The
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history also shows `hda-80862809-tplg.bin` and
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`hda-8086-generic-tplg.bin` being fetched, but they aren't present now
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and aren't needed; chell has no HDA codec.
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### 4. UCM `Syntax 7` → `Syntax 6`
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The cros UCM repo writes its files as `Syntax 7`, but neon's alsa-lib
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(`libasound2t64` 1.2.11) only understands up to `Syntax 6`, so
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`alsaucm -c avs_ssm4567 list _verbs` failed and PipeWire fell back to
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raw, unusable profiles. Fixed with:
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```
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sudo find /usr/share/alsa/ucm2/ -type f -exec sed -i 's/Syntax 7/Syntax 6/g' {} +
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```
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As of 2026-09-27 there are 0 `Syntax 7` files and `dpkg -V
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alsa-ucm-conf` reports no modified package files, so the sed only hit
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the cros files. **If the cros UCM is ever re-copied** (re-running
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`setup-audio`, or `cp -r alsa-ucm-conf-cros/ucm2/*`), re-run this sed,
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unless alsa-lib has been upgraded to a version that accepts Syntax 7.
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Then `systemctl --user restart wireplumber pipewire pipewire-pulse`
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(or reboot).
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## Reapplying on a fresh neon install
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```
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# 1. script: avs driver, cros UCM, wireplumber headroom
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git clone --depth 1 https://github.com/WeirdTreeThing/chromebook-linux-audio
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cd chromebook-linux-audio && sudo ./setup-audio
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# 2. topologies (not in Ubuntu's linux-firmware packages)
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BASE=https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/avs
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cd /lib/firmware/intel/avs && sudo wget $BASE/ssm4567-tplg.bin $BASE/nau8825-tplg.bin $BASE/dmic-tplg.bin
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# 3. UCM syntax downgrade for alsa-lib 1.2.11
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sudo find /usr/share/alsa/ucm2/ -type f -exec sed -i 's/Syntax 7/Syntax 6/g' {} +
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sudo reboot
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```
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Checks: `aplay -l` should list `avs_ssm4567` / `avs_nau8825`,
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`alsaucm -c avs_ssm4567 list _verbs` should print `HiFi`, and
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`wpctl status` should show the Speaker sink and the Internal Microphone
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source.
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## FydeOS on the eMMC has no audio
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Seen 2026-09-27, not investigated yet. The neon fixes don't carry over
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directly. FydeOS is ChromiumOS: a read-only verified rootfs, CRAS instead
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of PipeWire, and its own kernel and UCM. Things to check from a FydeOS
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shell (developer mode, or `crosh` → `shell`):
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- which DSP driver loaded (`lsmod | grep -E 'avs|sof|skl'`, `dmesg`)
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and whether `aplay -l` shows any cards;
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- whether `/lib/firmware/intel/avs/*-tplg.bin` exist there;
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- whether its UCM has `avs_ssm4567` etc. (`/usr/share/alsa/ucm2`).
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The same three pieces (driver selection, topologies, UCM) are the likely
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gaps.
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