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Mirrors phase6/step1/ from the ohm_gl_fix campaign. Contract-correct
hantro multi-planar / chromium-149-era stateless H.264 port of
bootlin's libva-v4l2-request, patches 0001..0018 + fourier-local.
Honest characterisation in README:
- Builds cleanly on chromium-builder LXC (boltzmann)
- vainfo enumerates H.264 profiles cleanly with LIBVA_DRIVER_NAME=v4l2_request
- NOT on Brave's decode path on ohm_gl_fix stack — Brave uses
Chromium's own V4L2VideoDecoder in media/gpu/v4l2/.
- Most likely useful for a future Firefox-via-libavcodec-vaapi
campaign, modulo a separate Mesa-panfrost WSI pitch issue.
- DEBUG patches (0010, 0011, 0014) intentionally kept in series
for development; remove for cleaner production runs.
Audit trail in the source repo at ohm_gl_fix:
phase6/step1/audit_0008_decode_params_2026-05-01.md
phase6/step1/api_contract_findings_2026-05-01.md
phase3_remeasure_2026-05-02/B3_decoder_discovery.md (why this
isn't on Brave's path)
215 lines
8.4 KiB
Diff
215 lines
8.4 KiB
Diff
From: Markus Fritsche <fritsche.markus@gmail.com>
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Date: 2026-05-02
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Subject: [PATCH] h264: gate SCALING_MATRIX submission on VAIQMatrixBuffer presence
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VAAPI signals "explicit scaling lists are present in the bitstream"
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implicitly: the consumer (ffmpeg-vaapi, mpv, etc.) sends a
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VAIQMatrixBufferH264 alongside RenderPicture iff
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sps_scaling_matrix_present_flag || pps_scaling_matrix_present_flag.
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When the bitstream uses default (flat) scaling, no IQMatrixBuffer
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arrives and the in-tree h264.matrix struct stays zero-initialised.
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fourier's existing codec_store_buffer for MPEG2 and HEVC tracks this
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via a per-surface iqmatrix_set boolean (surface.h::mpeg2.iqmatrix_set,
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h265.iqmatrix_set) — the H.264 path was missing the equivalent flag,
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so set_controls always submitted the scaling matrix, including the
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zero-initialised case.
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Symptom on hantro-vpu RK3568: when TRANSFORM_8X8_MODE is enabled in
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PPS, the kernel multiplies all 8x8 DCT coefficients by the zeroed
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scaling_list_8x8, producing a zeroed CAPTURE buffer despite a
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successful decode round-trip (no V4L2_BUF_FLAG_ERROR,
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bytesused=3655712 reported).
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Earlier draft of this patch unconditionally omitted SCALING_MATRIX in
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FRAME_BASED. That's corpus-correct (bbb has no explicit scaling
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lists) but the wrong predicate: the kernel-side gating is by
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"matrix-supplied vs. not," not by decode mode. Streams that signal
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explicit scaling lists must submit SCALING_MATRIX in either mode.
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Contract verification (audit_0008_decode_params_2026-05-01.md +
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hantro_h264.c::assemble_scaling_list): the kernel uses the supplied
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matrix when SCALING_MATRIX is in the control batch and falls back
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to spec-defined defaults when absent. Mode-independent.
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This patch:
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- surface.h: adds bool matrix_set to params.h264, mirroring
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mpeg2.iqmatrix_set / h265.iqmatrix_set.
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- picture.c codec_store_buffer (H.264 VAIQMatrixBufferType case):
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sets matrix_set = true when the buffer arrives.
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- picture.c RequestBeginPicture: resets matrix_set = false at the
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start of each Begin/Render/End cycle.
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- h264.c h264_set_controls: builds the controls[] array
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incrementally; SPS/PPS/DECODE_PARAMS always; SCALING_MATRIX iff
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matrix_set; SLICE_PARAMS only in SLICE_BASED; PRED_WEIGHTS only
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when both SLICE_BASED and V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED.
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The pre-existing FRAME_BASED-omits-SLICE_PARAMS rule is preserved —
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kernel doc ext-ctrls-codec-stateless.rst:752: "When this mode is
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selected, the V4L2_CID_STATELESS_H264_SLICE_PARAMS control shall
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not be set."
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Cross-reference: kernel UAPI section
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ext-ctrls-codec-stateless.rst V4L2_CID_STATELESS_H264_SCALING_MATRIX
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(matrix supplied iff explicit scaling lists in bitstream) and
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hantro_h264.c::assemble_scaling_list (consumes supplied matrix or
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falls back to defaults).
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Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>
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---
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--- a/src/surface.h
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+++ b/src/surface.h
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@@ -73,6 +73,7 @@
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} mpeg2;
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struct {
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VAIQMatrixBufferH264 matrix;
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+ bool matrix_set;
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VAPictureParameterBufferH264 picture;
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VASliceParameterBufferH264 slice;
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} h264;
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--- a/src/picture.c
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+++ b/src/picture.c
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@@ -153,6 +153,7 @@
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memcpy(&surface_object->params.h264.matrix,
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buffer_object->data,
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sizeof(surface_object->params.h264.matrix));
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+ surface_object->params.h264.matrix_set = true;
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break;
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case VAProfileHEVCMain:
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@@ -255,6 +256,7 @@
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surface_object->source_size = slot->size;
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surface_object->slices_size = 0;
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surface_object->slices_count = 0;
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+ surface_object->params.h264.matrix_set = false;
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surface_object->status = VASurfaceRendering;
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context_object->render_surface_id = surface_id;
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--- a/src/h264.c
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+++ b/src/h264.c
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@@ -553,66 +553,68 @@
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sps.profile_idc = h264_profile_to_idc(profile);
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/*
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- * Per-request control batch, ordered so the controls REQUIRED in
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- * V4L2_STATELESS_H264_DECODE_MODE_FRAME_BASED come first
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- * (indices 0..3) and the SLICE_BASED-only controls come last
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- * (indices 4..5).
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+ * Build the per-request control list incrementally:
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+ * - SPS, PPS, DECODE_PARAMS: always required (in either decode
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+ * mode).
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+ * - SCALING_MATRIX: gated on surface->params.h264.matrix_set,
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+ * i.e. the consumer sent a VAIQMatrixBufferH264 this frame.
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+ * This matches the H.264 spec: explicit scaling lists are
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+ * present iff sps_scaling_matrix_present_flag ||
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+ * pps_scaling_matrix_present_flag, in which case VAAPI
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+ * consumers send the matrix; otherwise the kernel uses
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+ * spec-defined defaults. Independent of FRAME_BASED /
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+ * SLICE_BASED.
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+ * - SLICE_PARAMS: SLICE_BASED only. Kernel doc
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+ * ext-ctrls-codec-stateless.rst (FRAME_BASED entry):
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+ * "When this mode is selected, the
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+ * V4L2_CID_STATELESS_H264_SLICE_PARAMS control shall not be
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+ * set." Submitting it under FRAME_BASED triggers cluster-
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+ * validation EINVAL at error_idx=count.
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+ * - PRED_WEIGHTS: SLICE_BASED + V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED.
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*
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- * Cross-reference: GStreamer gst-plugins-bad
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- * sys/v4l2codecs/gstv4l2codech264dec.c (commit 9e3e775,
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- * lines 1263-1304) gates SLICE_PARAMS and PRED_WEIGHTS on
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- * is_slice_based(self); under FRAME_BASED only SPS/PPS/
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- * SCALING_MATRIX/DECODE_PARAMS are submitted. The kernel
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- * parses the bitstream itself in FRAME_BASED mode; submitting
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- * per-slice controls in that mode triggers cluster-validation
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- * EINVAL at error_idx=count.
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- */
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- struct v4l2_ext_control controls[6] = {
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- {
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- .id = V4L2_CID_STATELESS_H264_SPS,
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- .p_h264_sps = &sps,
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- .size = sizeof(sps),
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- }, {
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- .id = V4L2_CID_STATELESS_H264_PPS,
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- .p_h264_pps = &pps,
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- .size = sizeof(pps),
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- }, {
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- .id = V4L2_CID_STATELESS_H264_SCALING_MATRIX,
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- .p_h264_scaling_matrix = &matrix,
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- .size = sizeof(matrix),
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- }, {
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- .id = V4L2_CID_STATELESS_H264_DECODE_PARAMS,
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- .p_h264_decode_params = &decode,
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- .size = sizeof(decode),
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- }, {
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- .id = V4L2_CID_STATELESS_H264_SLICE_PARAMS,
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- .p_h264_slice_params = &slice,
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- .size = sizeof(slice),
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- }, {
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- .id = V4L2_CID_STATELESS_H264_PRED_WEIGHTS,
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- .ptr = &weights,
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- .size = sizeof(weights),
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- }
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- };
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-
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- /*
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- * Decode-mode dispatch. Patch 0002 unconditionally sets the
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- * device to FRAME_BASED, so we hardcode that here. When the
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- * planned probe-then-set commit lands, slice_based becomes
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- * context->decode_mode == V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED
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- * with context->decode_mode populated at CreateContext via
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- * VIDIOC_QUERYCTRL/G_EXT_CTRLS.
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- *
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- * FRAME_BASED: 4 controls (SPS, PPS, SCALING_MATRIX, DECODE_PARAMS).
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- * SLICE_BASED: +SLICE_PARAMS (always), +PRED_WEIGHTS (when
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- * V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED).
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+ * Patch 0002 unconditionally sets the device to FRAME_BASED,
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+ * so slice_based is hardcoded false here. When the planned
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+ * probe-then-set commit lands, this becomes
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+ * context->decode_mode == V4L2_STATELESS_H264_DECODE_MODE_SLICE_BASED.
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*/
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+ struct v4l2_ext_control controls[6] = { 0 };
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+ unsigned int num_controls = 0;
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const bool slice_based = false; /* TODO: probe via context->decode_mode */
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- unsigned int num_controls = 4;
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+
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_SPS;
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+ controls[num_controls].p_h264_sps = &sps;
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+ controls[num_controls].size = sizeof(sps);
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+ num_controls++;
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+
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_PPS;
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+ controls[num_controls].p_h264_pps = &pps;
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+ controls[num_controls].size = sizeof(pps);
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+ num_controls++;
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+
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_DECODE_PARAMS;
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+ controls[num_controls].p_h264_decode_params = &decode;
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+ controls[num_controls].size = sizeof(decode);
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+ num_controls++;
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+
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+ if (surface->params.h264.matrix_set) {
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_SCALING_MATRIX;
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+ controls[num_controls].p_h264_scaling_matrix = &matrix;
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+ controls[num_controls].size = sizeof(matrix);
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+ num_controls++;
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+ }
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+
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if (slice_based) {
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- num_controls = 5;
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- if (V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED(&pps, &slice))
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- num_controls = 6;
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_SLICE_PARAMS;
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+ controls[num_controls].p_h264_slice_params = &slice;
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+ controls[num_controls].size = sizeof(slice);
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+ num_controls++;
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+
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+ if (V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED(&pps, &slice)) {
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+ controls[num_controls].id = V4L2_CID_STATELESS_H264_PRED_WEIGHTS;
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+ controls[num_controls].ptr = &weights;
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+ controls[num_controls].size = sizeof(weights);
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+ num_controls++;
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+ }
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}
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rc = v4l2_set_controls(driver_data->video_fd, surface->request_fd,
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