libva-multiplanar/README.md

# libva-multiplanar

Single-question campaign on the libva V4L2-stateless backend: **make multi-planar libva work, end-to-end, on Rockchip hantro hardware, for production VA-API consumers (Brave/Chromium, Firefox via libavcodec, mpv `--hwdec=vaapi`, vainfo as smoke test)**.

The deliverable is a libva-v4l2-request fork that any VA-API consumer can dlopen and get H.264 (initially) and MPEG-2 hardware-decoded NV12 dmabufs out of, on PineTab2 RK3568 first, with the same plumbing intended to extend to RK3399 (fresnel) and RK3588 (boltzmann/ampere) once the RK3568 path is solid.

The fork lives as a subdirectory of this campaign:

- [`libva-v4l2-request-fourier/`](libva-v4l2-request-fourier/) — clone of `bootlin/libva-v4l2-request` with our `master` ahead. Existing substrate: see its [`STUDY.md`](libva-v4l2-request-fourier/STUDY.md) for the build-cleanly + probe + control-flow + WIP-tracing work landed before this campaign opened.

This README is the Claude-facing entry point for resumption after compaction. Read it first.

## Origin

`fourier_attribution` campaign closed 2026-05-04 with the per-package wheat-vs-chaff verdict on bbb 1080p H.264 first-60s playback (PineTab2):

- **kwin-fourier**: WHEAT, robust. Removing it triples kwin CPU, drives Mali to 95 % peak-freq residency, doubles drops. Confirmed.
- **chromium-fourier**: WHEAT-but-fragile (Sonnet review's downgrade). Removing it (= falling back to stock Brave 1.89 / Chromium-147 base) costs 83 pp browser CPU (54 % → 137 %) — a magnitude consistent with **multi-planar libva enabling the hantro hardware-decode fast path**, but confounded with the Brave-147-vs-Chromium-149 base-version delta. Cell E (vanilla Chromium 149 control) was identified as the cheapest disambiguator and not yet run.
- **qt6-fourier**: CHAFF on this workload.

Phase 5 review: <https://dokuwiki.reauktion.de/doku.php?id=fourier:attribution_2026-05-03>

The chromium-fourier verdict's load-bearing claim is "multi-planar libva is the binding decode-side enabler on hantro." Whether that claim survives a clean control depends on this campaign's deliverable shipping. **The reverse is also true**: until a working multi-planar libva-v4l2-request lands, no consumer other than chromium-fourier-with-Step-1-patches has hardware decode on RK3568. Firefox VAAPI, mpv `--hwdec=vaapi`, gst-vaapi, vainfo all degrade to software or fall over.

## Process

Eight-plus-one phase loop per [`feedback_dev_process.md`](../../.claude/projects/-home-mfritsche-src/memory/feedback_dev_process.md). Phase 0 is locked in [`phase0_findings.md`](phase0_findings.md) — read that next. The fork's prior `STUDY.md` content was migrated into `phase0_findings.md` and the file in the fork is now a pointer (recover from commit `e0acc33` if historic content needed).

Phase 5 (second-model review via DokuWiki) and Phase 8 (memory entry) follow the predecessor cadence — invoke the Plan subagent with `model: sonnet` for the open-consultation review pattern (cf. `fourier_attribution` reviewer response).

Per the [`feedback_replicate_baseline_first.md`](../../.claude/projects/-home-mfritsche-src-kwin-overlay-subsurface/memory/feedback_replicate_baseline_first.md) lesson: any binding cell in this campaign anchors to in-session-acquired data. The migrated STUDY.md material and ohm_gl_fix patch-correctness audits are reference history, not threshold sources.

## Predecessor work that this campaign builds on

State (carry-over) — fork content, file:line pointers, contract analyses:

- [`libva-v4l2-request-fourier/STUDY.md`](libva-v4l2-request-fourier/STUDY.md) — Phase 0 / Phase 2 substrate already written, dated through 2026-05-02. Goal statement, why-the-fork-exists, build-cleanly stack of fixes, probe/control-flow fixes, eager-probe rationale, failure-mode-as-of-2026-04-26 (Brave-side wall is chromeos pipeline, not libva surface stack).
- [`libva-v4l2-request-fourier/`](libva-v4l2-request-fourier/) git history: 12 commits ahead of bootlin tip `a3c2476`, including kernel-UAPI renames, NV12 multi-plane format entry, V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE probe fallback, and recent (2026-05-02) WIP entry-point tracing for Brave's libva surface stack.
- [`~/src/ohm_gl_fix/phase6/step1/`](../ohm_gl_fix/phase6/step1/) — Step 1 patches 0001..0018, contract-correct port of libva-v4l2-request to hantro multi-planar / Chromium-149 era. Audit at `audit_0008_decode_params_2026-05-01.md`. **vainfo enumerates H.264 profiles cleanly on this binary; Brave's chromium-fourier 149 binary engages this libva path end-to-end** (per `fourier_attribution` cell A's 54 % browser CPU vs cell B's 137 %). Step 1 patches are the working substrate that this campaign should reconcile against the libva-v4l2-request-fourier `master` and either fold-in or supersede.
- [`~/src/ohm_gl_fix/`](../ohm_gl_fix/) — closed campaign, README documents the Step 1 audit and the test corpus (`bbb_1080p30_h264.mp4` etc.).
- [`~/src/fourier_attribution/`](../fourier_attribution/) — most recent campaign. Pay attention to:
  - Cell A (chromium-fourier on, libva-multi-planar engaged): browser_cpu_median = 54.4 %, fps = 24.0, drops_60s = 12.
  - Cell B (Brave 1.89 / Chromium 147, libva path absent or broken): browser_cpu_median = 137.15 %, fps = 23.18, drops_60s = 16.
  - `phase4_findings.md` for cross-cell verdict; `phase5_review_sonnet_2026-05-04.md` for the reviewer's pushback on the chromium-fourier conclusion.

Reference history (context, NOT data this campaign anchors to) — orthogonal scanout-plane constraint:

- [`~/src/kwin_overlay_subsurface/phase2_source_findings.md`](../kwin_overlay_subsurface/phase2_source_findings.md) — rockchip-drm RK3568 plane format/modifier table. **Plane 39 (Primary, NV12 LINEAR) is the only NV12-capable scanout; KWin owns it. Plane 45 (Overlay) advertises zero NV12.** Therefore: even when libva-multi-planar produces a clean NV12 dmabuf, no scanout plane is reachable while KWin runs, and some component must GL-composite NV12 → RGB before display. **This is orthogonal to libva**: libva is on the decode side, the scanout-plane gap is on the display side. They're separate problems with separate fixes.
- [`~/src/x11-session-research/phase0_evidence/x11_baseline_2026-05-03/x1_summary.md`](../x11-session-research/phase0_evidence/x11_baseline_2026-05-03/x1_summary.md) — confirms the scanout-plane gap isn't fixable by switching session servers either. mpv-xv {SW,HW} and mpv-gpu {SW,HW} all leave Plane 39 in XRGB8888 throughout. It's a kernel/Mesa/Xorg-DDX gap, not a hardware-decoding gap. **Don't expect this campaign to "fix the video pipeline end-to-end"** — fixing libva-multi-planar fixes the decode side; the scanout-plane question stays open after.
- [`~/src/kwin_overlay_subsurface/`](../kwin_overlay_subsurface/) — closed without patch (`phase8_handover.md`); its `feedback_replicate_baseline_first.md` lesson is the discipline that this campaign inherits.

External reference:

- Mozilla bug 1833354 / 1965646 (Firefox HW decode on RK3566/RK3588 explicitly needs libva-v4l2-request, not v4l2-m2m).
- Bootlin upstream `bootlin/libva-v4l2-request` — dormant since 2021, written for single-plane sunxi-cedrus.
- Collabora's `cros-codecs` (Rust, bypasses libva) — strategic replacement, not shipping soon.
- Other dormant forks (per `STUDY.md`): jernejsk, ndufresne, pH5, jc-kynesim, ArtSvetlakov — none ship multi-planar.

## In-scope (LOCKED 2026-05-04 in phase0_findings.md)

- libva-v4l2-request fork (`libva-v4l2-request-fourier/`), **backend only** — multi-planar correctness across the V4L2-stateless lifecycle: format probing (single-plane fallback to multi-plane), control protocol sequencing, surface-handle export, dmabuf modifier negotiation.
- H.264 first; MPEG-2 next. HEVC explicitly out.
- Hardware target: **ohm RK3568 hantro G1/G2 first iteration only.** fresnel RK3399 + ampere/boltzmann RK3588 explicit future iterations after ohm path is solid.
- Test consumers: vainfo, mpv `--hwdec=vaapi`, Firefox `media.ffmpeg.vaapi.enabled`, chromium-fourier 149 (regression check). Brave 1.89 deferred (chromeos-pipeline gating, not a libva-side problem).
- Phase 1 success criterion: **boolean correctness** — "libva accepted + providing access to hardware decoder". Performance metrics deferred to follow-up iteration.

## Out-of-scope (LOCKED 2026-05-04)

- Front-end libva (API library). Backend only.
- Other hardware: fresnel, ampere, boltzmann — separate iterations.
- HEVC, VP8, VP9, AV1 codecs.
- Performance metrics (CPU%, fps, drops_60s, panfrost freq).
- KWin / Wayland scanout-plane work — orthogonal (`kwin_overlay_subsurface` closed without patch).
- `cros-codecs` Rust replacement (per [`user_stance_rust.md`](../../.claude/projects/-home-mfritsche-src-fourier/memory/user_stance_rust.md)).
- Bootlin / Collabora upstreaming (per [`feedback_no_upstream.md`](../../.claude/projects/-home-mfritsche-src/memory/feedback_no_upstream.md)).

## Hardware target

- ohm — PineTab2, Rockchip RK3568 (4× Cortex-A55, Mali-G52 MP2, hantro G1/G2 VPU). Kernel `6.19.10-danctnix1-1-pinetab2`. **Primary measurement target.**
- (later) fresnel — Pinebook Pro, Rockchip RK3399 (hantro G1, no G2). EndeavourOS-ARM custom OC kernel — see [`reference_fresnel_kernel_constraints.md`](../../.claude/projects/-home-mfritsche-src-fourier/memory/reference_fresnel_kernel_constraints.md).
- (much later) ampere/boltzmann — RK3588 (hantro VDPU381). Adding VDPU381 is a code addition this fork doesn't have today.

## Non-upstreaming default

Inherited from the predecessors. Patches must be aligned to upstream in syntax and semantics, but no PR/MR/bug-report happens without explicit operator instruction. Bootlin upstream is dormant; once this campaign reaches a defensible state, Markus may wish to engage Bootlin / Collabora / Hans de Goede / Jernej Škrabec — that's a separate explicit decision.

## Repository layout

```
~/src/libva-multiplanar/                       <- this campaign (its own git repo for findings)
├── README.md                                  <- this file
├── (worklist.md, phase0_findings.md, ... — created as phases land)
└── libva-v4l2-request-fourier/                <- the actual fork (separate git repo)
    ├── .git/                                  <- origin: marfrit/libva-v4l2-request-fourier
    │                                              upstream: bootlin/libva-v4l2-request
    ├── STUDY.md                               <- pre-existing Phase 0/2 substrate
    └── src/                                   <- libva-v4l2-request source tree
```

The campaign repo and the fork repo are **separate git repositories** — campaign findings and fork commits are versioned independently. This matches the operator's general pattern (`ohm_gl_fix` campaign vs the bootlin fork it patched).

Operator-facing repo URL TBD: probably `git.reauktion.de/marfrit/libva-multiplanar` once the campaign produces something worth pushing. The fork is already at `git.reauktion.de/marfrit/libva-v4l2-request-fourier`.

## File map (will grow)

| File | What it is |
|---|---|
| `README.md` | This file |
| `phase0_findings.md` | **Read this next.** Locked research question, locked scope, predecessor state-vs-data discipline, Phase 0 inventory work-to-do, source-read references |
| `worklist.md` | Phase-by-phase task list (filled in as phases land) |
| `phase0_evidence/` | Phase 0 inventory + in-session baseline anchor (created when first run lands) |
| `libva-v4l2-request-fourier/` | The fork (separate repo: `marfrit/libva-v4l2-request-fourier`) |