The project's consumer-side goal landed: a real VAAPI consumer
(ffmpeg with -hwaccel vaapi) drives our libva backend → V4L2
driver → daemon → byte-exact NV12 output back to ffmpeg.
ffmpeg -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 \
-hwaccel_output_format nv12 -i vp9_small.ivf \
-f rawvideo -y /tmp/vp9_via_libva.nv12
cmp /tmp/vp9_via_libva.nv12 /tmp/vp9_ref_for_libva.nv12 → match
18432-byte NV12 byte-for-byte identical to plain ffmpeg
-pix_fmt nv12 software decode. The project_consumer_target
memory's deliverable shape — "V4L2 stateless node consumed by
a real VAAPI client" — is achieved.
Two related kernel changes:
1. v4l2_ctrl_handler_setup(&ctx->hdl) after registration —
matches rkvdec/cedrus/hantro. Brings each registered
compound control out of "uninitialised" state via
std_init_compound defaults.
2. Per-request control completion in the decode path —
the real fix for "Timeout when waiting for media request".
vb2-core's vb2_buffer_done unbinds the BUFFER's req_obj
on normal decode completion, but the per-request CONTROL
object stays bound. buf_request_complete fires only from
queue-cancel paths (vb2-core line 2284), NOT from normal
buf_done. The driver must call
v4l2_ctrl_request_complete(req, hdl) explicitly from the
completion path.
struct daedalus_inflight gained a `struct media_request
*req` field, captured from src_buf->vb2_buf.req_obj.req
in device_run. daedalus_complete_resp_frame then calls
v4l2_ctrl_request_complete before
v4l2_m2m_buf_done_and_job_finish — triggers
MEDIA_REQUEST_STATE_COMPLETE and wakes the request fd
poll.
For non-request flows (test_m2m_stream direct QBUF)
inf->req is NULL; the conditional skips the call.
Both consumer styles work concurrently.
Diagnostic clarification (was Phase 8.13a):
strace traced three S_EXT_CTRLS calls per frame:
1. H264_PROFILE + H264_LEVEL → EINVAL (we don't register)
2. HEVC_PROFILE + HEVC_LEVEL → EINVAL (we don't register)
3. VP9_FRAME + VP9_COMPRESSED_HDR → SUCCESS
The first two are harmless: libva probes whether we support
H264/HEVC integer profile/level controls during config
negotiation; we don't (we expose them as stateless), so EINVAL
just falls through. The actual VP9 stateless controls (#3)
succeeded all along — the libva-side "Unable to set control(s)"
log was misleading us into thinking the control path was the
bug.
Verification on hertz (Pi 5, 6.12.75+rpt-rpi-2712):
daemon log:
REQ_DECODE cookie=1 codec=1 bitstream=1566 bytes capture=128x96 1 planes
decoder: opened vp9 context
decoder: OK 128x96 fmt=0 (yuv420p) fnv1a=0x1eb34bfe ...
ffmpeg side:
no Timeout, no Decoding error
/tmp/vp9_via_libva.nv12: 18432 bytes
cmp vs reference: byte-for-byte identical.
Roadmap update:
- 8.10/8.11, 8.12, 8.13 marked closed with closure docs.
- 8.14 = multi-frame VP9 via libva, AV1 + H.264, mpv/Firefox
higher-level consumers.
Per correctness-before-speed:
- strace + kernel-source-reading found the actual root cause
rather than guessing.
- Conditional v4l2_ctrl_request_complete preserves the existing
test_m2m_stream non-request path — both consumer styles work
concurrently without per-flow branching elsewhere.
- Byte-exact pixel comparison, not "frame size matches."
Phase 8.14 next: multi-frame stream + multi-codec via libva +
mpv/Firefox.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
