# Audio on hp-chell (KDE neon)

Working state (verified 2026-09-27): speakers, headset jack and internal
mic work under neon. PipeWire/WirePlumber shows `Built-in Audio Speaker`
and `Built-in Audio Internal Microphone`, and the headset appears when
something is plugged in. None of this works out of the box. It took the
fixes below, all applied **2026-03-05**, reconstructed on 2026-09-27
from `~/.bash_history` and file timestamps.

## Hardware

HP Chromebook 13 G1 ("chell", Skylake). The audio DSP is Intel Skylake
SST, driven by the kernel's **`avs`** driver (`snd_soc_avs`), with three
board-specific machine drivers. Each one is its own ALSA card:

| Card | Driver | What |
|---|---|---|
| `avs_ssm4567` | `snd_soc_avs_ssm4567` | speakers: 2x ADI SSM4567 amps |
| `avs_nau8825` | `snd_soc_avs_nau8825` | headset jack: Nuvoton NAU88L25 codec |
| `avs_dmic` | `snd_soc_avs_dmic` | internal digital mic |
| `avs_probe_mb` | `snd_soc_avs_probe` | DSP debug probe, not a real device |

The cards report the long name `Google-Chell-1.0`.

Speaker safety: the upstream script disables speakers on Chromebooks
with a **MAX98357A** amp (no volume limiter, so it can blow the
speakers). Chell uses **SSM4567**, not MAX98357A, so that doesn't apply
and the speakers are enabled.

## The fixes

### 1. WeirdTreeThing's `chromebook-linux-audio` script

Checkout: `~/github/chromebook-linux-audio`
(<https://github.com/WeirdTreeThing/chromebook-linux-audio>, shallow
clone at `8c7e15e`, 2026-02-16). Run as `sudo ./setup-audio -b chell`.
`-b` is the branch of the UCM repo to clone, and there's no `chell`
branch; a plain `./setup-audio` is what's intended. For a Skylake board
(`skl`/`kbl`/`apl`) it:

- **Switches the DSP driver to `avs`**:
  `/etc/modprobe.d/snd-avs.conf`
  ```
  options snd-intel-dspcfg dsp_driver=4
  options snd-soc-avs ignore_fw_version=1
  options snd-soc-avs obsolete_card_names=1
  ```
  `dsp_driver=4` selects `avs`. Without it `snd-intel-dspcfg` picks
  legacy HDA or SOF, and neither works on chell. `obsolete_card_names=1`
  gives the `avs_ssm4567`-style card names that the UCM profiles below
  match on.
- **Installs Chromebook UCM profiles**: clones
  <https://github.com/WeirdTreeThing/alsa-ucm-conf-cros> and copies
  `ucm2/` into `/usr/share/alsa/ucm2/`, and `overrides/` into
  `/usr/share/alsa/ucm2/conf.d/`. The ones this board uses are
  `conf.d/avs_ssm4567/`, `conf.d/avs_nau8825/` and `conf.d/avs_dmic/`
  (`avs_ssm4567/HiFi.conf` sets amp boost, the master volumes at 219,
  and `Left/Right Speaker Switch`).
- **Adds WirePlumber headroom**:
  `/etc/wireplumber/wireplumber.conf.d/51-increase-headroom.conf` sets
  `api.alsa.headroom = 2048` on all `alsa_output.*` nodes (the script
  says it fixes instability and crashes on these DSPs).
- Runs `alsactl init`.

### 2. Duplicate modprobe option (harmless)

`/etc/modprobe.d/inteldsp.conf`: `options snd-intel-dspcfg dsp_driver=4`,
written by hand a few minutes before the script ran. It duplicates the
first line of `snd-avs.conf`. You can delete it.

### 3. AVS topology files, downloaded by hand

The `avs` driver needs a per-board **topology** blob for each machine
driver. Ubuntu's `linux-firmware-intel-misc` ships only the base DSP
firmware (`/lib/firmware/intel/avs/skl/dsp_basefw.bin.zst` plus one
module), not the topologies, and the script doesn't provide them
either. They were fetched straight from upstream linux-firmware:

```
cd /lib/firmware/intel/avs/
BASE=https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/avs
sudo wget $BASE/ssm4567-tplg.bin $BASE/nau8825-tplg.bin $BASE/dmic-tplg.bin
```

Installed: `ssm4567-tplg.bin`, `nau8825-tplg.bin` and `dmic-tplg.bin`
(not owned by any package, so apt won't update or remove them). The
history also shows `hda-80862809-tplg.bin` and
`hda-8086-generic-tplg.bin` being fetched, but they aren't present now
and aren't needed; chell has no HDA codec.

### 4. UCM `Syntax 7` → `Syntax 6`

The cros UCM repo writes its files as `Syntax 7`, but neon's alsa-lib
(`libasound2t64` 1.2.11) only understands up to `Syntax 6`, so
`alsaucm -c avs_ssm4567 list _verbs` failed and PipeWire fell back to
raw, unusable profiles. Fixed with:

```
sudo find /usr/share/alsa/ucm2/ -type f -exec sed -i 's/Syntax 7/Syntax 6/g' {} +
```

As of 2026-09-27 there are 0 `Syntax 7` files and `dpkg -V
alsa-ucm-conf` reports no modified package files, so the sed only hit
the cros files. **If the cros UCM is ever re-copied** (re-running
`setup-audio`, or `cp -r alsa-ucm-conf-cros/ucm2/*`), re-run this sed,
unless alsa-lib has been upgraded to a version that accepts Syntax 7.

Then `systemctl --user restart wireplumber pipewire pipewire-pulse`
(or reboot).

## Reapplying on a fresh neon install

```
# 1. script: avs driver, cros UCM, wireplumber headroom
git clone --depth 1 https://github.com/WeirdTreeThing/chromebook-linux-audio
cd chromebook-linux-audio && sudo ./setup-audio

# 2. topologies (not in Ubuntu's linux-firmware packages)
BASE=https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/plain/intel/avs
cd /lib/firmware/intel/avs && sudo wget $BASE/ssm4567-tplg.bin $BASE/nau8825-tplg.bin $BASE/dmic-tplg.bin

# 3. UCM syntax downgrade for alsa-lib 1.2.11
sudo find /usr/share/alsa/ucm2/ -type f -exec sed -i 's/Syntax 7/Syntax 6/g' {} +

sudo reboot
```

Checks: `aplay -l` should list `avs_ssm4567` / `avs_nau8825`,
`alsaucm -c avs_ssm4567 list _verbs` should print `HiFi`, and
`wpctl status` should show the Speaker sink and the Internal Microphone
source.

## FydeOS on the eMMC has no audio

Seen 2026-09-27, not investigated yet. The neon fixes don't carry over
directly. FydeOS is ChromiumOS: a read-only verified rootfs, CRAS instead
of PipeWire, and its own kernel and UCM. Things to check from a FydeOS
shell (developer mode, or `crosh` → `shell`):
- which DSP driver loaded (`lsmod | grep -E 'avs|sof|skl'`, `dmesg`)
  and whether `aplay -l` shows any cards;
- whether `/lib/firmware/intel/avs/*-tplg.bin` exist there;
- whether its UCM has `avs_ssm4567` etc. (`/usr/share/alsa/ucm2`).
The same three pieces (driver selection, topologies, UCM) are the likely
gaps.