Phase 8.13: byte-exact end-to-end via libva (consumer target hit)

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>

kernel/daedalus_v4l2_main.c

@@ -520,6 +520,14 @@ struct daedalus_inflight {
 	struct daedalus_ctx	*ctx;
 	struct vb2_v4l2_buffer	*src_buf;
 	struct vb2_v4l2_buffer	*dst_buf;
+	/*
+	 * Captured media_request the src_buf was bound to (if any).
+	 * Set by device_run from src_buf->vb2_buf.req_obj.req;
+	 * consumed by the completion path to call
+	 * v4l2_ctrl_request_complete + signal request fd.  NULL for
+	 * non-request flows (e.g. test_m2m_stream direct QBUF).
+	 */
+	struct media_request	*req;
 };
 
 static struct daedalus_inflight *
@@ -666,6 +674,14 @@ static void daedalus_device_run(void *priv)
 	inf->ctx	= ctx;
 	inf->src_buf	= src_buf;
 	inf->dst_buf	= dst_buf;
+	/*
+	 * Capture the bound media_request (if any) so the
+	 * completion path can call v4l2_ctrl_request_complete +
+	 * trigger MEDIA_REQUEST_STATE_COMPLETE.  vb2-core's normal
+	 * buf_done path unbinds the buffer's req_obj but leaves the
+	 * control object bound — the driver has to complete it.
+	 */
+	inf->req	= src_buf->vb2_buf.req_obj.req;
 
 	mutex_lock(&dev->inflight_lock);
 	list_add_tail(&inf->list, &dev->inflight);
@@ -789,6 +805,22 @@ void daedalus_complete_resp_frame(u32 cookie,
 		}
 	}
 
+	/*
+	 * Phase 8.14: if the src_buf was bound to a media_request
+	 * (libva-driven decode path), complete the per-request
+	 * control state BEFORE buf_done_and_job_finish.  vb2-core's
+	 * buf_done unbinds the buffer's req_obj on its own, but the
+	 * control object stays bound until v4l2_ctrl_request_complete
+	 * runs — only after BOTH objects unbind does the request
+	 * transition to MEDIA_REQUEST_STATE_COMPLETE and wake any
+	 * userspace poll on the request fd.
+	 *
+	 * For non-request flows (test_m2m_stream direct QBUF) inf->req
+	 * is NULL and v4l2_ctrl_request_complete just no-ops.
+	 */
+	if (inf->req)
+		v4l2_ctrl_request_complete(inf->req, &inf->ctx->hdl);
+
 	/*
 	 * Use the buf_done_and_job_finish helper rather than plain
 	 * buf_done + job_finish: the helper pops the buffers off
@@ -968,6 +1000,15 @@ static int daedalus_open(struct file *file)
 
 	v4l2_ctrl_handler_init(&ctx->hdl, ARRAY_SIZE(daedalus_stateless_ctrls));
 	daedalus_register_stateless_ctrls(&ctx->hdl);
+	/*
+	 * v4l2_ctrl_handler_setup runs s_ctrl for every registered
+	 * control with its default value — required to bring each
+	 * control out of "uninitialised" state.  Without this the
+	 * per-request handler clone path returns EINVAL on
+	 * VIDIOC_S_EXT_CTRLS(which=REQUEST_VAL).  rkvdec/cedrus/
+	 * hantro all call this after registration.
+	 */
+	v4l2_ctrl_handler_setup(&ctx->hdl);
 	ctx->fh.ctrl_handler = &ctx->hdl;
 
 	daedalus_fill_output_fmt(&ctx->src_fmt,