Document neon audio fixes (avs driver, topologies, cros UCM)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-09-27 13:05:00 -04:00
parent c7231628b8
commit f55d51fccc
2 changed files with 155 additions and 0 deletions
@@ -0,0 +1,144 @@
+# 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.
@@ -137,3 +137,14 @@ Quick reference:
  directly.
 - ChromeOS updates re-add a UEFI entry and put it first in `BootOrder`;
  see `CHROMEOS-FLEX.md`.
+
+## Audio (neon)
+
+Speakers, headset jack and mic work under neon thanks to custom fixes
+applied 2026-03-05, documented in **`AUDIO.md`**: WeirdTreeThing's
+`chromebook-linux-audio` script (`avs` driver via
+`/etc/modprobe.d/snd-avs.conf`, cros UCM profiles, WirePlumber
+headroom), avs topology blobs hand-downloaded from upstream
+linux-firmware into `/lib/firmware/intel/avs/`, and a `Syntax 7` →
+`Syntax 6` sed over the UCM files for neon's alsa-lib 1.2.11. FydeOS on
+the eMMC has no audio yet (not investigated).