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marfrit c7f6fb90cb Phase 8.6: dmabuf + AV1 + H.264 + stateless controls

Removes the Phase 8.5 64 KiB frame-size cap by exporting CAPTURE
buffers as dmabuf-fds the daemon mmaps and writes pixels into
directly. Adds AV1 + H.264 codec support, V4L2 stateless control
registration, and the compliance polish that brings the driver
to 47/48 v4l2-compliance pass.

Protocol (include/daedalus_v4l2_proto.h):
- struct daedalus_req_decode grew capture-buffer metadata
  (width/height/pix_fmt/num_planes + per-plane size+stride).
- New DAEDALUS_IOC_GET_DMABUF ioctl on the chardev: daemon
  asks for a per-plane dmabuf fd, kernel calls vb2_core_expbuf
  in daemon task context so the fd lands in the daemon's table.

Kernel m2m driver (kernel/daedalus_v4l2_main.c):
- Both queues switched to vb2_dma_contig_memops. OUTPUT was
  vmalloc in 8.5; the switch is needed because vmalloc doesn't
  honour V4L2_MEMORY_FLAG_NON_COHERENT and v4l2-compliance's
  REQBUFS test rejected the driver because of it. We still
  read bitstream via vb2_plane_vaddr (dma_contig gives a
  kernel virtual address just like vmalloc did).
- dma_coerce_mask_and_coherent(DMA_BIT_MASK(32)) in probe.
- queue_setup populates alloc_devs[plane] = &pdev->dev for
  both queues; allow_cache_hints=1 on both.
- daedalus_export_capture_dmabuf(cookie, plane, flags, *fd):
  walks inflight list, calls vb2_core_expbuf on the CAPTURE
  buffer in the caller's (daemon's) task context.
- device_run fills the new REQ_DECODE capture fields from
  ctx->dst_fmt and maps ctx->src_fmt.pixelformat to
  DAEDALUS_CODEC_VP9 / _AV1 / _H264 (was hard-wired to VP9).
- daedalus_complete_resp_frame handles both the 8.5 inline
  path (kept for debugging) and the 8.6 dmabuf path (pixels
  already in CAPTURE buffer, just set payload from metadata).
- enum_fmt advertises all 3 OUTPUT formats (VP9F, AV1F, S264).
- try_fmt preserves userspace colorspace fields instead of
  overwriting with REC709 defaults (fixes 8.5 compliance fail).
- s_fmt propagates OUTPUT colorspace → CAPTURE (stateless
  decoder round-trip test at v4l2-test-formats.cpp:958).
- 12 V4L2 stateless controls registered per open (VP9_FRAME,
  VP9_COMPRESSED_HDR, H264_SPS/PPS/SCALING/PRED_WEIGHTS/
  SLICE_PARAMS/DECODE_PARAMS, AV1_FRAME/SEQUENCE/
  TILE_GROUP_ENTRY/FILM_GRAIN). Daemon ignores values (FFmpeg
  re-parses); registration is what makes libva-v4l2-request
  see us.

Kernel chardev (kernel/daedalus_v4l2_chardev.c):
- New unlocked_ioctl dispatching DAEDALUS_IOC_GET_DMABUF to
  daedalus_export_capture_dmabuf.
- debugfs test_decode cookies unified with the m2m cookie
  allocator via shared daedalus_next_cookie() — kills the
  Phase 8.5 namespace collision.

Daemon (daemon/src/...):
- New dmabuf_capture.{c,h}: GET_DMABUF + mmap each plane on
  REQ_DECODE; munmap + close on completion. O_RDWR | O_CLOEXEC
  is essential — vb2_core_expbuf extracts O_ACCMODE from flags
  and exports read-only by default (caught on first run; mmap
  -EACCES on PROT_WRITE).
- decoder.{c,h}: lazily opens AV1 + H.264 AVCodecContexts in
  addition to VP9 (dropped the -ENOSYS stubs). pack_nv12_to_planes
  writes Y line-by-line into planes[0] with planes[0].stride;
  interleaves Cb/Cr into planes[1] with planes[1].stride.
- chardev_client.c handle_req_decode: opens dmabuf planes,
  runs decode (pixels land in CAPTURE buffer directly), closes
  planes, sends metadata-only RESP_FRAME. No wire-pixel
  allocation.

Test harness (tools/test_m2m_decode.c):
- Optional 5th arg `codec` (vp9 | av1 | h264). Same client
  drives all three codecs.

Verification on hertz (Pi 5, 6.12.75+rpt-rpi-2712):

Bit-exact end-to-end vs `ffmpeg -pix_fmt nv12`:
  VP9   1920x1080  3,110,400 bytes  MATCH
  AV1     128x96      18,432 bytes  MATCH
  H.264   128x96      18,432 bytes  MATCH

VP9 1080p went through the full dmabuf path with no chardev
payload bloat — the same chardev that capped at 64 KiB in 8.5
now ferries metadata only and lets the daemon mmap+write a
3.1 MB frame directly into the V4L2 client's buffer.

v4l2-compliance:
  Phase 8.1: 44/48
  Phase 8.5: 44/48 (different fails after m2m landed)
  Phase 8.6: 47/48
  Only remaining: VIDIOC_(TRY_)DECODER_CMD (needs media
  controller — explicitly Phase 8.7 work).

11 standard compound controls visible:
  vp9_frame_decode_parameters, vp9_probabilities_updates,
  h264_sequence_parameter_set, h264_picture_parameter_set,
  h264_scaling_matrix, h264_prediction_weight_table,
  h264_slice_parameters, h264_decode_parameters,
  av1_sequence_parameters, av1_frame_parameters,
  av1_film_grain (av1_tile_group_entry refused by hdl->error
  on this kernel — skipped silently).

Clean SIGTERM + rmmod, no oops/WARN.

Roadmap update (docs/roadmap.md):
- Phase 8.6 marked closed with the closure-doc reference.
- Phase 8.7 reshaped to (1) media controller, (2) perf +
  daedalus_dispatch_* substitution, (3) HDR/10-bit, (4)
  long-form multi-frame streaming.

Per correctness-before-speed:
- Real V4L2 dmabuf via vb2_core_expbuf (not a sideband
  fd-passing hack).
- O_RDWR access mode threaded through correctly.
- Strict pixel-byte comparison against ffmpeg, not "looks
  right" eyeballing.
- Each compliance edge documented with the underlying test
  source-line + the fix.
- All resource paths cleaned (munmap + close per plane on
  every exit, including error paths).

Phase 8.7 next: media controller binding (closes last
compliance fail), per-frame profiling, QPU dispatch
substitution targeting 30fps@1080p from
30fps-floor-is-fine memory.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-18 16:16:06 +00:00

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daedalus-v4l2 — roadmap

Sub-phases

Phase 8.1 — kernel module skeleton

Out-of-tree kernel module that:

Registers /dev/videoNN with VFL_TYPE_VIDEO + a no-op V4L2 stateless dispatch table.
Accepts open/close, S_FMT, REQBUFS ioctls without doing anything (yet).
Builds against /lib/modules/$(uname -r)/build.

Deliverable: modprobe daedalus_v4l2 works, v4l2-ctl --list-devices shows the new device.

Phase 8.2 — kernel ↔ daemon chardev bridge

Kernel module creates /dev/daedalus-v4l2 chardev.
Defines a simple req/resp protocol in include/daedalus_v4l2_proto.h.
Daemon connects, exchanges echo requests.

Deliverable: ping-pong test passes.

Phase 8.3 — daemon FFmpeg dlopen + parse

Daemon links libdaedalus_core.a from sibling.
Daemon dlopens FFmpeg.
Test program: feed a VP9 IVF file to FFmpeg parsers, extract block-level metadata, validate against expected.

Deliverable: daemon can parse a VP9 frame and walk the block-level info.

Phase 8.4 — daemon ↔ kernel decode round-trip (closed 2026-05-18)

Shipped as a debugfs-triggered chardev round-trip rather than the original V4L2-ioctl plan (which moved to Phase 8.5).

REQ_DECODE / RESP_FRAME wire protocol
Daemon decodes VP9 via FFmpeg dlopen, returns FNV-1a digest
Verified content-dependent + deterministic; structured error handling for bad bitstreams

See docs/phase_8_4_closure.md.

Phase 8.5 — full V4L2 m2m driver (closed 2026-05-18)

Real V4L2 m2m driver — userspace clients drive S_FMT/REQBUFS/QBUF/DQBUF the standard way. Bitstream flows kernel→daemon as inline REQ_DECODE payload; decoded NV12 pixels flow daemon→kernel as inline RESP_FRAME payload. Works end-to-end for small frames (≤ ~64 KiB NV12).

Deliverable hit: kernel m2m driver passes most v4l2-compliance checks; tools/test_m2m_decode produces a NV12 frame that's byte-for-byte identical to ffmpeg -pix_fmt nv12 reference.

See docs/phase_8_5_closure.md.

Phase 8.6 — dmabuf + AV1 + H.264 + stateless controls (closed 2026-05-18)

CAPTURE (and OUTPUT) on vb2_dma_contig_memops.
New DAEDALUS_IOC_GET_DMABUF chardev ioctl — daemon mmaps the in-flight CAPTURE buffer, decodes pixels in place, sends RESP_FRAME metadata-only.
64 KiB frame-size cap removed. 1080p VP9 + 128×96 AV1
- 128×96 H.264 all byte-exact against reference FFmpeg decode.
V4L2 stateless controls registered for VP9 / AV1 / H.264 (11 controls visible to userspace).
Colorspace round-trip fix (TRY_FMT preserve, S_FMT OUTPUT→CAPTURE propagation).
Cookie unified across V4L2 + debugfs paths.
v4l2-compliance: 47/48 (only DECODER_CMD remains, needs media controller — moved to 8.7).

See docs/phase_8_6_closure.md.

Phase 8.7 — media controller, perf, HDR, long-form streams

Media controller binding via v4l2_m2m_register_media_controller (closes the last v4l2-compliance fail and unlocks the request API).
Profile the daemon's per-frame cost on hertz; substitute daedalus_dispatch_* for FFmpeg's per-block paths where the kernel implementation matches. Target the 30fps-floor-is-fine memory's daily-YouTube criterion: 30fps@1080p with CPU left over for vscode.
HDR / 10-bit support — P010M CAPTURE, depth-aware pack_nv12_to_planes.
Long-form multi-frame streaming tests (B-frame refs, GOP boundaries) — current test client is one keyframe per run.

Deliverable: 30fps stable on real content + full compliance pass.

Effort estimate

Each phase: ~1 week of focused work (~40 hours). Total: 7 weeks for v1.

Could be split across multiple sessions / contributors.

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