cd34ec19180344e1e040dcab26eda2b523f38283
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 claude-noether
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b3ba157cb4 |
iter2 Phase 2: situation analysis — six bugs in HEVC path
Phase 2 source-read of the HEVC path post-iter1-close (fork master
229d6d1). Six bugs identified, all in libva backend; kernel + driver
path proven for HEVC in Phase 0 cross-validator sweep.
Substrate timing caveat: Phase 2 conducted against fresnel kernel
6.19.9-99. Operator-scheduled rolling pacman -Syyuu to linux-7
imminent. Phase 2 source-read findings are kernel-agnostic (fork
code + UAPI + FFmpeg reference); they carry forward across the
kernel jump unchanged. Phase 3 baselines will run on linux-7.
Bug 1 — src/config.c:64-69 HEVCMain falls through to default,
returns VA_STATUS_ERROR_UNSUPPORTED_PROFILE. Verbatim match for
iter1 Bug 1 pattern; fix is 3-line break addition.
Bug 2 — src/picture.c:204-206 explicit
case VAProfileHEVCMain: return UNSUPPORTED_PROFILE
with stale comment "Fourier-local: HEVC stripped, no HW support
on RK3566." (RK3566 is ohm context; fresnel is RK3399 where
rkvdec DOES support HEVC.) Fix: replace explicit reject with
dispatch to h265_set_controls() (mirrors MPEG-2 dispatch at
picture.c:186-191).
Bug 3 — src/h265.c uses staging-era CIDs:
V4L2_CID_MPEG_VIDEO_HEVC_PPS / _SPS / _SLICE_PARAMS
These don't exist on fresnel's 6.19 kernel headers (verified via
test-compile: gcc reports undeclared identifiers, suggests
V4L2_CID_MPEG_VIDEO_DEC_PTS as nearest match). Mainline kernel
UAPI splits HEVC stateless into 7 controls:
V4L2_CID_STATELESS_HEVC_{SPS,PPS,SLICE_PARAMS,SCALING_MATRIX,
DECODE_PARAMS,DECODE_MODE,START_CODE}
+ ENTRY_POINT_OFFSETS, EXT_SPS_ST_RPS, EXT_SPS_LT_RPS
(0xa40a90..0xa40a96 + extensions, V4L2_CID_CODEC_STATELESS_BASE
+ 400..407+).
Fix shape: rewrite h265.c against new split API. Substantially
larger than iter1's mpeg2.c rewrite (HEVC has 7 controls vs MPEG-2
3, + slice_params dynamic-array, + per-slice accumulation logic
needed).
Bug 4 — h265.c uses single-slice_params shape; new API is
dynamic-array. Fresnel rkvdec advertises:
hevc_slice_parameters 0xa40a92 elems=1 dims=[600] dynamic-array
Up to 600 slice_params entries per submission. Current
codec_store_buffer:115-135 OVERWRITES previous slice on
VASliceParameterBufferType arrival. Multi-slice frames need
APPEND-not-overwrite. FFmpeg reference v4l2_request_hevc.c:540-547
shows the pattern.
Fix shape: extend params.h265 to hold slice_params array (or
pointer+count); codec_store_buffer appends; h265_set_controls
flushes the array at end_picture as a single dynamic-array
S_EXT_CTRLS entry.
Bug 5 — h265.c missing controls: doesn't submit DECODE_PARAMS
(per-frame DPB info; new in modern API), SCALING_MATRIX (conditional
on iqmatrix_set + sps.scaling_list_enabled), DECODE_MODE+START_CODE
(device-wide menus, set once per context init).
Fix shape: add h265_fill_decode_params() (DPB ordering from VAAPI
ReferenceFrames[15] — preserve current extraction logic from
h265_fill_slice_params:269-315, route to new struct). Conditional
SCALING_MATRIX from VAIQMatrixBufferHEVC. Device-wide
DECODE_MODE+START_CODE either at first h265_set_controls call or
in extended context.c device-init block.
Bug 6 — src/meson.build comments out 'h265.c' (line 50) and
'h265.h' (line 73). Fix: uncomment both. Trivial.
Bug 7 (verify only) — include/hevc-ctrls.h is a 9-line shim that
just #include <linux/v4l2-controls.h>. Comment dates the
modernization to "linux-media 6.6+". Adds zero value; harmless.
Leave in place per iter1 Phase 5 Nit 6 lower-risk path.
Bug 8 (latent) — picture.c:287 params.h264.matrix_set=false
writes union byte 240. For HEVC: byte 240 lands inside
h265.picture (range [0..604), size 604) — different field than
MPEG-2's chroma_intra_quantiser_matrix. ffmpeg-vaapi's
per-frame VAPictureParameterBufferHEVC re-send overwrites the
corrupted byte before h265_set_controls reads. Latent for
clients that reuse a surface without re-sending picture params.
iter2+ Phase 4 cross-cutting backlog candidate; not iter2 scope.
Things verified NOT bugs:
- h265_fill_pps/sps/slice_params field extraction from VAAPI
structs is sound (just routes to wrong destination structs)
- NAL header parsing (data_bit_offset bit-search) is preserved
in new API — slice_params still has bit_size + data_bit_offset
- v4l2_set_controls batching API in place (used by H.264 + iter1
MPEG-2; iter2 uses same)
Substrate / kernel observation:
- Linux mainline 7.1.0-rc2 reference checkout has
drivers/staging/media/rkvdec/ with rkvdec.c, rkvdec-h264.c,
rkvdec-vp9.c — NO rkvdec_hevc.c. fresnel's HEVC support is
out-of-tree (Christian Hewitt patches per phase0_findings.md
external references). May land in stable 7.x.
- Phase 4 contract-before-code therefore can't cite kernel-side
HEVC handler source until/unless rkvdec_hevc.c lands in
mainline. UAPI doc + FFmpeg reference + Phase 3 cross-validator
bytes are the contract anchor.
Open questions tabled for Phase 3 (post-linux-7-upgrade):
1. iter1 + T4 references on linux-7 (regression check of closed
iter1 work)
2. SDDM watchpoint on linux-7
3. Cross-validator HEVC re-anchor (Baseline C equivalent for
HEVC) — verbatim payload bytes for SPS, PPS, DECODE_PARAMS,
SLICE_PARAMS array, SCALING_MATRIX
4. Pre-fix scratch test (Bug 1 + Bug 2 only, h265.c kept
commented out) — confirm collateral safe
5. Slice-count for bbb_720p10s_hevc.mp4 fixture
6. Whether linux-7 brings rkvdec_hevc.c into mainline
Predicted iter2 close shape: trivial Bugs 1+2+6 fixes + sizable
h265.c rewrite (~250-400 lines, ~3x iter1's mpeg2.c) + new
codec_store_buffer slice accumulation logic. If Phase 7 fails:
likely struct-size mismatch (run pahole), DPB ordering, or
slice_params array size encoding.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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