fresnel-fourier/phase8_iteration23_close.md

Iteration 23 — Phase 8 (close)

Closes 2026-05-14. iter23 = kernel printk inside v4l2_ctrl_request_setup outer loop, BEFORE the continue check, logging every iteration. FULL close.

Method

linux-fresnel-fourier 7.0-7 added one pr_info at TOP of the outer loop in v4l2_ctrl_request_setup, BEFORE if (ref->req_done || (ctrl->flags & V4L2_CTRL_FLAG_READ_ONLY)) continue;:

pr_info("iter23_loop: id=0x%x req_done=%d flags=0x%x ncontrols=%d cluster0_id=0x%x\n",
    ctrl->id, ref->req_done, ctrl->flags,
    master->ncontrols,
    master->cluster[0] ? master->cluster[0]->id : 0);

Result — definitive

libva HEVC (first setup): iter23_loop fires for 16 IDs ending at 0xa40a90 (HEVC_SPS). The outer loop EXITS before reaching 0xa40a91.

kdirect HEVC (first setup): iter23_loop fires for 22 IDs ending at 0xa40a96 (HEVC_START_CODE). The outer loop completes normally.

The loop body has only two exit-loop paths after the iter23_loop printk fires:

1. goto error if req_to_new(r) returns non-zero.
2. break if try_or_set_cluster(NULL, master, true, 0) returns non-zero.

For libva, ONE of these fires AT HEVC_SPS, exiting the loop. For kdirect, NEITHER fires.

This fully overturns iter21/22:

• The clone-hdl IS complete for libva (iter22 confirmed all 22 controls cloned).
• The setup loop reaches HEVC_SPS for libva (iter23 confirmed).
• The processing of HEVC_SPS in the setup loop FAILS for libva.

The failure of HEVC_SPS processing means:

• p_cur for HEVC_SPS is never committed → rkvdec reads zero (iter20 finding).
• All subsequent compound HEVC controls (PPS, SLICE_PARAMS, SCALING_MATRIX, DECODE_PARAMS, DECODE_MODE, START_CODE) NEVER reach their processing → their req_done stays false but they're also never committed → all zero in ctx->ctrl_hdl.

Why does HEVC_SPS processing fail for libva but not kdirect?

The most likely candidates:

Function	Failure modes
req_to_new(ref_SPS)	-ENOENT if !p_req_valid. -EINVAL if elem count mismatch (p_req_elems != p_array_alloc_elems for non-dyn-array). -ENOMEM if alloc fails for dyn-array resize.
try_or_set_cluster(NULL, master_SPS, true, 0)	Validator failures (out-of-range field values). Cluster ops failures. Often returns -EINVAL or -ERANGE.

iter24 will pinpoint which function fails and what return value.

iter21/22's interpretation errors

• iter21: I concluded the clone-hdl was missing controls. Wrong — the iter21_setup_ref printk was inside the loop body but AFTER the early-continue check. The "missing" controls were actually iterated past after SPS's processing failed and the loop exited — they never even saw the iter21 printk.
• iter22: The clone trace confirmed clone-hdl is complete. Good. But my mid-conclusion ("clone-hdl is complete; staging fails in setup loop SKIP path") was partially wrong — the loop doesn't SKIP, it EXITS.

Mechanism status (post-iter23)

#	Mechanism	Status
1	request_fd mismatch	DISPROVED iter17/18
2	REINIT clears	DISPROVED iter19
3	Stack-locals stale	DISPROVED iter18
4	ctrl_hdl mismatch	DISPROVED iter20-22
5	error_idx silent failure	DISPROVED iter18
6	req->p_new staging incomplete	DISPROVED iter22
7	Clone-hdl missing controls	DISPROVED iter22
8	Skip-loop bypass	DISPROVED iter23 (loop EXITS, not skips)
9	NEW iter23: HEVC_SPS processing in v4l2_ctrl_request_setup fails for libva	LEADING — iter24 candidate

iter24 candidate

linux-fresnel-fourier 7.0-8:

ret = req_to_new(r);
pr_info("iter24_req_to_new: id=0x%x ret=%d p_req_valid=%d p_req_elems=%u\n",
    master->cluster[i]->id, ret, r->p_req_valid, r->p_req_elems);
...
ret = try_or_set_cluster(NULL, master, true, 0);
pr_info("iter24_try_or_set: master_id=0x%x ret=%d\n", master->id, ret);

After 7.0-8 deploys, libva HEVC will show:

• iter24_req_to_new id=0xa40a90 ret=X p_req_valid=Y p_req_elems=Z where X is the actual return value.
• If req_to_new ret != 0 → bug is in req_to_new for HEVC_SPS on libva's staged data. Compare p_req_elems to kdirect's value.
• If req_to_new ret == 0 → check iter24_try_or_set's ret. If non-zero → validator rejects libva's SPS but accepts kdirect's. Investigate which field validator rejects.

Substrate state at iter23 close

• Backend SHA on fresnel: c1d4bb53… (iter15 stable, unchanged).
• Fork tip e109306 — unchanged.
• Kernel linux-fresnel-fourier 7.0-7 with iter17 + iter20 + iter21 + iter22 + iter23 printks.
• 5-codec anchors: unchanged.

iter24 build kicked off

linux-fresnel-fourier 7.0-8 building on boltzmann (PID 1672261, log /tmp/iter24-kbuild.log).

Lesson

Three iterations of mid-loop printk (iter21, iter22, iter23) needed to localize the exit. Each iteration overturned the previous's partial conclusion. Key methodology: place the diagnostic printk at the very top of each loop body, BEFORE any continue/break, to distinguish "skipped" from "exited". Without that, "missing from printk output" is ambiguous.

The bug is now localized to:

• A specific function: req_to_new OR try_or_set_cluster.
• A specific control: HEVC_SPS.
• A specific request lifecycle pattern: libva's, not kdirect's.

One more printk iteration (iter24) should give the failing function + return code.