84 lines
4.8 KiB
Markdown
84 lines
4.8 KiB
Markdown
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# Pixel 3 (blueline) — loudspeaker routing fix
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**Status:** SOLVED 2026-07-12 — pmOS routing applied; fix lives in Pixel3Arch rootfs-overlay UCM (commit 2f39c06) + alsactl store. Both speakers verified by ear.
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**Goal:** Make the loud bottom speaker work. Right now sound only comes from the
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top **earpiece**; the loud bottom-firing speaker never fires. Casey reports
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postmarketOS had audio working but with the channels "reversed".
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## Device / stack
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- Google Pixel 3 (blueline), sdm845, mainline kernel `7.1.1-sdm845` (built 2026-07-11)
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- Souveraine OS (Arch Linux ARM), Hyprland/Wayland
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- ALSA card 0 = "Google Pixel 3" (`G3`)
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- Audio: PipeWire 1.6.7 (PulseAudio shim)
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- Speakers: **dual Cirrus CS35L36** amps ("Left"/"Right") on `QUAT_TDM_RX_0` (MultiMedia1)
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- Earpiece amp: WCD9340 `EAR PA` (separate codec)
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## Key config files
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- Active UCM (system): `/usr/share/alsa/ucm2/Google/blueline/HiFi.conf`
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- referenced by `/usr/share/alsa/ucm2/conf.d/sdm845/Google-Pixel-3.conf`
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- **Only defines a "Speaker" device. No earpiece device. Never sets Channel Mux.**
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- Intended fix location: **user override** under `~/.config/alsa/ucm2/...`
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(Casey chose user-override so pacman updates to alsa-ucm-conf don't clobber it.)
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- Baseline ALSA state snapshot saved to scratchpad as `asound-current.state`
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(scratchpad is ephemeral — re-capture with `alsactl -f <file> store 0` if needed).
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## What we PROVED (via live tone tests)
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1. Both CS35L36 amps are healthy; both transducers (earpiece + loud speaker)
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can physically produce sound.
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2. **The 30% volume / SUSPENDED sink was a huge red herring** — many "silent"
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test results were just low volume. ALWAYS test at `pactl set-sink-volume
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@DEFAULT_SINK@ 100%` and un-suspend the sink first.
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3. Default state: both amps have `Channel Mux = RX1` (numid 121 Left, 112 Right).
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=> both amps pull the same slot => only earpiece is audible.
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4. `EAR PA Volume`=0 did NOT silence the earpiece output => the sound you hear
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from the "earpiece" is being driven by a **CS35L36 amp**, not the WCD EAR PA.
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5. At 100% vol, an L-only vs R-only test: **one channel DID come out the loud
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bottom speaker.** So the loudspeaker amp works — it just needs the right
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channel/slot routed to it. (Casey couldn't reliably tell L vs R by ear.)
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6. BUT: simply splitting `Left Channel Mux=RX1 / Right Channel Mux=RX2` and
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playing duplicated-mono did NOT wake the loudspeaker in a later test.
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=> The channel→amp mapping is UPSTREAM of `Channel Mux`, on the QUAT_TDM_RX_0
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TDM bus. `Channel Mux` alone is not the whole story.
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## Relevant mixer controls (card 0, by numid)
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- 121 `Left Channel Mux` (enum: 0=RX1, 1=RX2) — default 0
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- 112 `Right Channel Mux` (enum: 0=RX1, 1=RX2) — default 0
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- 122 `Left AMP Enable Switch` / 113 `Right AMP Enable Switch` (default on)
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- 123 `Left BOOST Enable Switch` / 114 `Right BOOST Enable Switch`(default on)
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- 18 `EAR PA Volume` (WCD earpiece amp; default 4)
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- CS35L36 input source slots: `Left/Right ASPTX1..6SRC` (both amps identical:
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1SRC=2, 2SRC=3, 3SRC=5, 4SRC=6, 5SRC=4, 6SRC=0)
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- UCM SectionVerb enables: `QUAT_TDM_RX_0 Audio Mixer MultiMedia1` = 1
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## NEXT STEP (where we stopped)
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Get postmarketOS's authoritative blueline mixer mapping — pmOS works, so its
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UCM / mixer_paths is the source of truth. The most relevant is the pmaports
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**7.1rc1 kernel MR (!8446)** because that matches this exact kernel (7.1.x):
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- https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/8446
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- Device/blueline MR: https://gitlab.com/postmarketOS/pmaports/-/merge_requests/3932
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- Original Pixel 3 device MR (!5514): https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5514
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- pmOS SDM845 audio writeup: https://postmarketos.org/edge/2023/01/11/sdm845-audio/
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- pmOS Audio wiki (xml2ucm / mixer_paths.xml -> UCM): https://wiki.postmarketos.org/wiki/Audio
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Find in pmOS's config: which TDM slot / channel each CS35L36 amp is fed, and
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whether it sets `Channel Mux` + the TDM RX slot routing so earpiece(top) and
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loudspeaker(bottom) each get a distinct channel. Then encode that as a user UCM
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override in `~/.config/alsa/ucm2/` (copy blueline HiFi.conf there, add the
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Channel Mux / slot csets to the Speaker device's EnableSequence).
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## HOW TO TEST (repeatable)
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```sh
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pactl set-sink-volume @DEFAULT_SINK@ 100% # ALWAYS — 30% masks everything
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pactl set-sink-mute @DEFAULT_SINK@ 0
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# distinct L/R tones already generated in scratchpad: left.wav right.wav stereo.wav
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paplay left.wav ; paplay right.wav
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# read/toggle mux:
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amixer -c 0 cget numid=121 # Left Channel Mux
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amixer -c 0 cset numid=112 1 # Right -> RX2
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```
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Restore baseline: both muxes -> 0, EAR PA -> 4, volume -> 30%.
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## CAUTION
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- Don't trust "silent" results unless volume is 100% and sink un-suspended.
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- Reverse-engineering the TDM routing blind was NOT converging. Read the pmOS
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config first, then change mixers — don't guess.
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