FP3 on mainline Linux: one BSP-side pointer needed to unblock audio (SLIMbus framer) — before support ends in August

Participate Development
1

Hi all,

TL;DR: Mainline Linux (postmarketOS) runs well on the FP3 — display, GPU, WiFi, modem, cameras all work. The one big missing piece is audio through the WCD9326 codec (earpiece, calls, mic): the ADSP never starts the SLIMbus framer on a mainline boot, even though the identical stock firmware does so on the Android/downstream boot. We have exhaustively ruled out the AP/kernel side and are stuck at a question only someone with Qualcomm BSP access can answer.

Full technical report with all the evidence (register decodes, working-vs-failing traces, QMI byte-comparison, firmware analysis) is here:
:backhand_index_pointing_right: FP3 (SDM632/msm8953): WCD9326 (Tasha-lite) SLIMbus framer never comes up on mainline — earpiece/in-call/mic silent · Issue #255 · msm8953-mainline/linux · GitHub

What we’re asking from Fairphone (or anyone with SDM632 BSP/QXDM access):

  1. What — beyond the QMI SELECT_INSTANCE+POWER_REQ handshake (which is byte-identical and ACKed on both stacks) — makes the ADSP actually start framing the SLIMbus and broadcast MASTER_CAPABILITY? A device.cfg/ACDB flag, an SMD/GLINK handshake, a boot parameter?
  2. Ideally: a QXDM / ADSP diag F3 capture of the SLIMbus framer bring-up on a working stock boot. The diag .dci message database is build-specific, so this is the one artifact the community cannot produce on its own.

Why now: official FP3 software support concludes in August. After that, community projects like postmarketOS are what keeps these phones alive — very much in the spirit of Fairphone’s longevity mission. Audio is the last blocker for the FP3 being a usable mainline-Linux daily driver, and one pointer from someone who shipped the SDM632 audio BSP would likely unblock it for the whole msm8953/sdm6xx family.

If any current or former Fairphone software folks are around (or can forward this internally), we’d be very grateful. Happy to run any experiment — we have instrumented mainline and downstream kernels booting side-by-side on the same device with full register-level access on both.

Thanks!

(Previous related thread: “Getting Linux on Fairphone 3: DTS / Hardware specification” — now auto-closed, hence the new topic.)

2

Please def send this to Fairphone directly to support, however PM OS already has the direct compnay connection

3

Thanks @yvmuell! I’ve filed it with Fairphone support and asked them to
forward it to the software/BSP team — ticket #1453513, referencing this
topic and the GitHub issue.

Good point on the postmarketOS connection — I’ll also raise it through the
pmOS side so it can reach Fairphone via the existing company contact. If the
two routes meet in the middle, even better :slight_smile: