claude-noether
2651e4cfdf
header parser requirement
Source-read of every file the iter4 patch series will touch, plus
kernel UAPI + VAAPI + downstream FFmpeg + kernel rkvdec reference
sources. Conducted on noether against fork tip e1aca9c (iter3 close).
Critical scope-shaping finding: rkvdec on RK3399 REQUIRES
V4L2_CID_STATELESS_VP9_COMPRESSED_HDR (not optional). Per
drivers/staging/media/rkvdec/rkvdec-vp9.c::rkvdec_vp9_run_preamble
lines 752-754:
ctrl = v4l2_ctrl_find(&ctx->ctrl_hdl,
V4L2_CID_STATELESS_VP9_COMPRESSED_HDR);
if (WARN_ON(!ctrl))
return -EINVAL;
VAAPI does NOT expose compressed-header probability updates
(va_dec_vp9.h:50-192 — only frame parameters + segmentation;
vendor VAAPI drivers parse compressed header in firmware/GPU).
Therefore the libva backend MUST parse the compressed header
itself via a VPX boolean decoder + inv_map_table[]. ~150-200 LOC
of bitstream parsing logic (port from FFmpeg
v4l2_request_vp9.c::fill_compressed_hdr).
Bug enumeration (12 sites):
B1 config.c::RequestQueryConfigProfiles enum block missing
B2 config.c::RequestCreateConfig VP9 case missing
B3 config.c::RequestQueryConfigEntrypoints VP9 case missing
B4 src/vp9.c new file ~500-600 LOC
B5 src/vp9.h new file ~35-45 LOC
B6 src/vp9_rac.h NEW or inline (Phase 4
plan locks Option A:
inline in vp9.c)
B7 picture.c::codec_set_controls VP9 dispatch missing
B8 picture.c::codec_store_buffer 2 buffer-type cases
(Picture + Slice;
NOT 4 like VP8)
B9 picture.c::RequestBeginPicture predicted no reset
needed (no flag-state
like VP8 iqmatrix_set)
B10 surface.h::object_surface::params union vp9 member missing
B11 meson.build vp9.c/vp9.h not in lists
B12 buffer.c predicted no change
needed (VP9 uses
Picture/Slice/SliceData
— all whitelisted)
Non-bugs (intentionally untouched): context.c (no DECODE_MODE/
START_CODE menus per FFmpeg ref), video.c (CAPTURE-side format
list), v4l2.c (fourcc-agnostic), include/hevc-ctrls.h (already
includes <linux/v4l2-controls.h>).
Contract surface cited verbatim:
V4L2_CID_STATELESS_VP9_FRAME = 0xa40b2c (~144 bytes — much
smaller than VP8's 1232 bytes because VP9_FRAME carries no
entropy table; that's in COMPRESSED_HDR)
V4L2_CID_STATELESS_VP9_COMPRESSED_HDR = 0xa40b2d (~1947 bytes
— coef[4][2][2][6][6][3] alone is 1728 bytes)
Per-frame submission: 2 controls batched in single S_EXT_CTRLS
v4l2_request_vp9.c references confirmed: 2-control shape,
runtime-probed COMPRESSED_HDR availability (rkvdec advertises
it; we MUST provide)
VAAPI buffer types: 2 per frame (Picture + Slice) vs iter3 VP8's
4. NO Probability buffer (VP9 keeps probs in compressed header).
NO IQMatrix (VP9 keeps quant in slice's per-segment seg_param[8]).
VAAPI → V4L2 mapping table: 30+ fields enumerated. Several gap
candidates identified for Phase 3 empirical resolution:
Q1 lf.ref_deltas/mode_deltas/flags — not in VAAPI; FFmpeg reads
from VP9Context internal. BBB likely zero.
Q2 quant.base_q_idx + deltas — VAAPI exposes only effective
per-segment scales. Inverse-derive needed.
Q3 reference_mode — not in VAAPI. Default to SELECT?
Q4 interpolation_filter mapping (FFmpeg ^ remap)
Q5 reset_frame_context off-by-one (FFmpeg > 0 ? - 1 : 0)
Q6 Per-segment feature_data[8][4] derivation from VAAPI's
effective scales is non-trivial
Q7 mpv 0.41.0 VP9 hwdec engagement (per memory feedback_hw_
decode_engagement_check.md — known gap from iter3 VP8)
Q8 rkvdec dma_resv issue? (predicted NO based on iter1+iter2
successful mpv-DMA-BUF-GL on rkvdec)
Patch-shape prediction: ~580-690 LOC across 5 modified + 2 new
files (closer to iter2 HEVC's 470 than iter3 VP8's 370). Compressed-
header parser is the dominant cost.
Phase 3 baseline targets queued: cross-validator strace verbatim
S_EXT_CTRLS payloads (both controls), VAAPI consumer trace, mpv-
VP9-vaapi engagement check, rkvdec readback non-zero check.
Phase 4 plan structure anticipated: 10-clause template per
iter2/iter3, with new Clause 8 dedicated to compressed-header
parser.
Refs:
phase0_findings_iter4.md (Phase 1 lock)
phase8_iteration3_close.md (predecessor)
references/ffmpeg-kwiboo/libavcodec/v4l2_request_vp9.c (V4L2 ref)
references/ffmpeg-kwiboo/libavcodec/vaapi_vp9.c (VAAPI ref)
/home/mfritsche/src/linux-rfc/drivers/staging/media/rkvdec/
rkvdec-vp9.c (kernel driver — confirms COMPRESSED_HDR
requirement at lines 752-754)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
fresnel-fourier
TL;DR
Peer campaign to libva-multiplanar, targeting fresnel (Pinebook Pro / Rockchip RK3399) instead of ohm (PineTab2 / RK3566). Same deliverable shape — make libva-v4l2-request-fourier work end-to-end, for production VA-API consumers — but on a different SoC with a different (and broader) V4L2 decoder surface.
The libva backend fork itself (libva-v4l2-request-fourier) is shared: it lives at ../libva-multiplanar/libva-v4l2-request-fourier/. This campaign does not nest a second copy. Code-side work that turns out to be RK3399-specific lands either as #ifdef/runtime-detected paths inside that fork's master or, if scope diverges sharply, on a feature branch — Phase 2 source-read of each iteration decides.
Origin
libva-multiplanar reached iter5-close on 2026-05-05 with the ohm path solid: hantro (rk3568-vpu DT compatible) decodes H.264 to NV12 dmabufs end-to-end, three iterations of bugs fixed, mpv --hwdec=vaapi smooth, firefox-fourier RDD-sandboxed Firefox engages the backend without MOZ_DISABLE_RDD_SANDBOX=1, chromium-fourier 149 confirmed as the regression-check consumer.
That campaign's README explicitly names fresnel (RK3399) and ampere/boltzmann (RK3588) as "future iterations after ohm path is solid" (libva-multiplanar/README.md:87). fresnel-fourier is the formal peer campaign for the RK3399 leg of that promise.
Topology choice (LOCKED 2026-05-07): peer campaign, not child of libva-multiplanar. Each runs its own 8(+1) phase loop. Cross-link only — fresnel-fourier results do not gate libva-multiplanar's Phase 8 close (which already happened iteration-by-iteration on ohm).
Hardware target
fresnel — Pinebook Pro laptop. See reference_fresnel_kernel_constraints.md for the custom-OC-kernel discipline (don't let pacman -Syu clobber the OC DTB) and project_fresnel.md for fleet placement.
| Property | Value |
|---|---|
| SoC | Rockchip RK3399 (2× Cortex-A72 + 4× Cortex-A53) |
| GPU | Mali-T860 MP4 (Midgard, panfrost) |
| Decoder block 1 | rkvdec (/dev/video3) — H.264 + HEVC + VP9 |
| Decoder block 2 | hantro-vpu-dec (rk3399-vpu-dec, /dev/video5) — MPEG-2 + VP8 (RK3399 hantro does not advertise H.264; corrected 2026-05-07 from empirical V4L2 enumeration — see phase0_evidence/2026-05-07/v4l2_inventory_findings.md) |
| Encoder block | hantro-vpu-enc (/dev/video4) — JPEG only |
| OS | EndeavourOS-ARM (Arch derivative; same pacman + marfrit-packages mechanism as ohm) |
| Kernel | linux-eos-arm 6.19.9-99 — CONFIG_FTRACE=y, CONFIG_FUNCTION_TRACER=y, CONFIG_DYNAMIC_FTRACE=y, CONFIG_TRACING=y verified 2026-05-07. No rebuild needed for trace work. |
The decode-side surface area is genuinely broader than ohm. ohm has hantro (H.264 + MPEG-2 + VP8) and an rkvdec block whose mainline rkvdec2/vdpu346 driver isn't merged. fresnel has hantro (MPEG-2 + VP8 only — empirical, see correction note in the table above) plus a fully-driven mainline rkvdec covering H.264 + HEVC + VP9. So this campaign exercises codecs (HEVC, VP9) the libva-v4l2-request-fourier fork has never run on real hardware to date, and there is exactly one decoder bind for H.264 (rkvdec) — no two-block routing decision.
GPU side: panfrost on Mali-T860 (Midgard) is a different generation than ohm's Mali-G52 (Bifrost). KWin / Mesa / panfrost stack regressions or wins on T860 are not assumed to track G52 — the kwin-fourier verdict from fourier_attribution doesn't transfer for free.
Scope (LOCKED 2026-05-07 in phase0_findings.md)
In scope:
- libva-v4l2-request-fourier backend exercised on fresnel V4L2 decode nodes (
rkvdec+hantro-vpu-dec). - Codecs: everything decode-capable — H.264 + HEVC + VP9 (via rkvdec) + MPEG-2 + VP8 (via hantro-vpu-dec). This is the explicit broadening from libva-multiplanar's H.264-first locked scope.
- Test consumers:
vainfo,mpv --hwdec=vaapi, Firefox viamedia.ffmpeg.vaapi.enabled, chromium-fourier 149 (regression check). - Phase 1 success criterion (matching libva-multiplanar): boolean correctness — "libva accepted + providing access to hardware decoder for each codec." Performance metrics deferred.
- Phase 0 task 1: recover fresnel from the SDDM greeter crash-loop (per
~/.claude/plans/dynamic-forging-piglet.md). Recovery is bookkept as substrate work inside this campaign, not as a separate prereq.
Out of scope:
- Front-end libva (API library). Backend only.
- Other hardware (ohm + ampere/boltzmann are libva-multiplanar's iterations).
- AV1 (no decoder block on RK3399 supports it).
- Performance metrics — fresnel CPU/GPU benchmarking is a separate iteration after correctness lands.
cros-codecsRust replacement (peruser_stance_rust.md).- Bootlin / Collabora upstreaming default-deferred (per
feedback_no_upstream.md). Same discipline as libva-multiplanar. - KWin / panfrost / Mali-T860 work — orthogonal until proven otherwise; a parallel
kwin-fourier-fresnelcampaign would be a separate decision.
Process
8(+1) phase loop per feedback_dev_process.md. Phase 0 substrate is in phase0_findings.md. Phase 5 review uses the sonnet-architect subagent pattern (Plan with model: sonnet).
In-session-acquired data discipline per feedback_replicate_baseline_first.md: libva-multiplanar's ohm-side measurements are reference history, not threshold sources for fresnel-fourier cells.
Predecessor work this campaign builds on
../libva-multiplanar/— five closed iterations on ohm. Read in order:README.md— current state, codec scope, file map.phase8_iteration5_close.md— most recent close. The iter5-end backend is the substrate fresnel-fourier starts from.phase0_findings.md(andphase0_findings_iter[2-5].md) — locked-scope precedent for codec breadth and consumer matrix on ohm; useful frame-of-reference when locking fresnel-side scope.phase8_iteration1_close.md— iter1 surface-export DMA-BUF lifecycle race + multi-resolution cache + 64-pitch alignment bugs. Likely re-surface candidates on RK3399.
../libva-multiplanar/libva-v4l2-request-fourier/— the fork itself. 12 commits ahead of bootlin tip plus iter1..iter5 work.git logfor the actual landing record.~/.claude/plans/dynamic-forging-piglet.md— fresnel SDDM greeter crash diagnosis + recovery plan. Phase 0 task 1 picks up from here.~/src/fourier_attribution/— ohm-only attribution matrix. The chromium-fourier WHEAT-but-fragile verdict and Cell E (vanilla Chromium 149 control) item are ohm-side context, not fresnel data.
External reference (carry-over from libva-multiplanar):
- Mozilla bug 1833354 / 1965646 (Firefox HW decode on RK35xx via libva-v4l2-request).
- Bootlin upstream
bootlin/libva-v4l2-request— dormant since 2021. - Linux kernel
drivers/staging/media/rkvdec/— RK3399 rkvdec H.264/HEVC/VP9 control protocol reference. - Linux kernel
drivers/media/platform/verisilicon/hantro_*— RK3399-vpu-dec MPEG-2/H.264/VP8 control protocol reference.
Repository layout
~/src/fresnel-fourier/ <- this campaign (its own git repo)
├── README.md <- this file
├── phase0_findings.md <- locked research question + Phase 0 work list
├── (worklist.md, phase[2-8]*.md as phases land)
└── (the libva fork is NOT here — see ../libva-multiplanar/libva-v4l2-request-fourier/)
The campaign repo and the fork repo stay separate. fresnel-fourier commits its findings here; code changes to the backend land on the fork's master (or a branch named per the iteration if scope diverges from libva-multiplanar's ohm-side master).
Operator-facing repo URL: git.reauktion.de/marfrit/fresnel-fourier — created empty during scaffolding, no push until first iteration finds something worth publishing.
Non-upstreaming default
Inherited from libva-multiplanar / feedback_no_upstream.md. Patches must be aligned to upstream in syntax and semantics; PR/MR/bug-report only on explicit operator instruction.
Build infrastructure
distcc/cross-build path is the existing fleet: aarch64crosscompiler LXD on data, tesla LXD on hertz, dcc1 on dcw3. See reference_distcc_kernel_builds.md for invocation. Per the locked Phase 0 answer for libva-multiplanar (item 9), no distcc for libva builds — libva is small and links fast, hand-build on fresnel directly. Same default applies here unless a specific reason emerges.
For chromium-fourier 149 / firefox-fourier rebuilds against fresnel-side findings, the boltzmann LXD container path from libva-multiplanar iter3 is reusable.