cd34ec19180344e1e040dcab26eda2b523f38283
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 claude-noether
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cc55a6e60a |
iter1 Phase 2: situation analysis — three bugs in MPEG-2 path
Phase 2 source-read of the libva-v4l2-request-fourier MPEG-2 path
on master tip 65969da identifies three independent bugs, all in
the libva backend (kernel + driver path proven solid by Phase 0
cross-validator sweep).
Bug 1 — fall-through to default in RequestCreateConfig
(src/config.c:55-69):
case VAProfileH264*:
// FIXME
break;
case VAProfileMPEG2Simple:
case VAProfileMPEG2Main:
case VAProfileHEVCMain:
default:
return VA_STATUS_ERROR_UNSUPPORTED_PROFILE;
H.264 cases have a break, MPEG-2 + HEVC fall through to default.
This explains the vaCreateConfig: 12 (UNSUPPORTED_PROFILE) error
observed in Phase 0 cross-validator sweep for both codecs.
Likely history: H.264 was libva-multiplanar focus iter1-iter5;
the FIXME comment suggests profile-specific validation logic was
expected but never landed. MPEG-2 stayed in fall-through bucket.
Fix shape: add break for MPEG-2 cases. HEVC stays in fall-through
(h265.c excluded from build per Phase 0 finding F-C; honest
UNSUPPORTED_PROFILE is correct until h265.c is reinstated in a
later iteration).
Bug 2 — staging-era UAPI in mpeg2.c; mainline kernel removed it:
src/mpeg2.c uses:
V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (V4L2_CID_MPEG_BASE+250 = 0x9909fa)
V4L2_CID_MPEG_VIDEO_MPEG2_QUANTIZATION (V4L2_CID_MPEG_BASE+251 = 0x9909fb)
Mainline kernel UAPI (include/uapi/linux/v4l2-controls.h:1985-2105):
V4L2_CID_STATELESS_MPEG2_SEQUENCE (CODEC_STATELESS_BASE+220 = 0xa409dc)
V4L2_CID_STATELESS_MPEG2_PICTURE (CODEC_STATELESS_BASE+221 = 0xa409dd)
V4L2_CID_STATELESS_MPEG2_QUANTISATION (CODEC_STATELESS_BASE+222 = 0xa409de)
Fresnel V4L2 inventory confirms kernel exposes the new IDs only.
The fork's local include/mpeg2-ctrls.h is the staging-era header
that masks the kernel's modern definitions.
Six structural changes from old to new API:
1. Slice header parsing moved to kernel — bit_size, data_bit_offset,
quantiser_scale_code GONE from new structs.
2. Reference timestamps moved from slice to picture
(forward_ref_ts, backward_ref_ts now in v4l2_ctrl_mpeg2_picture).
3. Boolean fields collapsed into v4l2_ctrl_mpeg2_picture.flags
bitmask (TOP_FIELD_FIRST, FRAME_PRED_DCT, CONCEALMENT_MV,
Q_SCALE_TYPE, INTRA_VLC, ALT_SCAN, REPEAT_FIRST, PROGRESSIVE).
4. progressive_sequence collapsed into
v4l2_ctrl_mpeg2_sequence.flags & V4L2_MPEG2_SEQ_FLAG_PROGRESSIVE.
5. PICTURE_CODING_TYPE renamed to PIC_CODING_TYPE
(V4L2_MPEG2_PICTURE_CODING_TYPE_X → V4L2_MPEG2_PIC_CODING_TYPE_X).
6. Quantisation load_* flags removed; matrices always present;
British spelling — quantiSation not quantiZation.
Quantisation matrix order: kernel doc says zigzag scanning order;
VAAPI VAIQMatrixBufferMPEG2 also stores in zigzag scanning order;
direct memcpy works. Kernel hantro_mpeg2.c does the
zigzag-to-raster permutation kernel-side
(hantro_mpeg2_dec_copy_qtable lines 12-26). No userspace
permutation needed in the libva backend (unlike FFmpeg, which
unwinds its internal idsp.idct_permutation order).
Per-frame submission: FFmpeg reference (libavcodec/
v4l2_request_mpeg2.c:130-155) batches 3 controls in single
VIDIOC_S_EXT_CTRLS. Backend's v4l2_set_controls (src/v4l2.c:475)
already supports batching — used by iter6/7/8 H.264
(src/h264.c:986). MPEG-2 rewrite follows H.264's batched pattern.
Bug 3 — include/mpeg2-ctrls.h is the staging-era local header:
The fork's local include/mpeg2-ctrls.h is the staging-era header
that defines the old (removed) API. config.c:37 + mpeg2.c:38
include it via meson's include_directories('../include'). Should
be deleted (or emptied); rely on kernel <linux/v4l2-controls.h>
pulled transitively via <linux/videodev2.h>.
Things verified NOT to be bugs:
- src/picture.c MPEG-2 dispatch is fully wired:
- codec_store_buffer handles VAPictureParameterBuffer + VAIQMatrix
- codec_set_controls dispatches MPEG-2 to mpeg2_set_controls
- HEVC explicitly UNSUPPORTED_PROFILE (correct for build state)
- src/picture.c:287 unconditional h264.matrix_set=false reset is
benign for MPEG-2 (union aliasing puts it in mpeg2.picture or
.slice region; RenderPicture overwrites that byte before
mpeg2_set_controls reads anything).
- src/mpeg2.c field extraction from VAAPI structs is sound; only
the destination control IDs and struct shape need rewiring.
- src/v4l2.c batching API (v4l2_set_controls) is in place.
Open questions tabled for Phase 3 baseline:
1. Live ftrace of failing libva MPEG-2 attempt post Bug-1-fix
(verify expected EINVAL on VIDIOC_S_EXT_CTRLS for old CID).
2. VAAPI VAIQMatrixBufferMPEG2 matrix order from real mpv decode
(verify zigzag, no pre-permutation).
3. Cross-reference verbatim VIDIOC_S_EXT_CTRLS payload from
ffmpeg-v4l2request cross-validator anchor strace dump.
4. SDDM watchpoint resolution — fresnel SSH No route to host at
Phase 2 start (network event, SDDM regression, or operator
power-state). Resolve before Phase 3.
Predicted iter1 outcome: small mechanical diff (config.c break
+ mpeg2.c rewrite + drop local mpeg2-ctrls.h). Phase 7 verification
should land all 5 Phase 1 boolean checks green on first or second
try. Likely Phase 7 → Phase 4 loopback triggers if any: forgotten
struct padding zero, garbage timestamps on first I-frame, or
device-state precondition we missed in hantro_mpeg2.c.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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