test0r
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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)
59 lines
2.6 KiB
Diff
59 lines
2.6 KiB
Diff
From: Markus Fritsche <fritsche.markus@gmail.com>
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Date: 2026-05-01
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Subject: [PATCH] surface: don't VIDIOC_S_FMT the CAPTURE queue
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The hantro stateless decoder derives the CAPTURE format from the
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SPS attached to the per-request OUTPUT controls. Calling
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VIDIOC_S_FMT on the CAPTURE queue at vaCreateSurfaces2 time can
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leave the driver's vb2 state in an inconsistent configuration
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where the queue accepts buffers and DQBUF returns successfully but
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the kernel never actually writes decoded pixels into them.
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Cross-reference: GStreamer's gst-plugins-bad/sys/v4l2codecs/
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gstv4l2decoder.c only calls VIDIOC_G_FMT on the CAPTURE side
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(via gst_v4l2_decoder_negotiate_src_format and friends). The
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same code path produces correctly-decoded NV12 frames on the
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same RK3568 hantro-vpu where libva-v4l2-request-with-S_FMT
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emits flat-green zeroed CAPTURE buffers.
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The v4l2_get_format() call immediately after this block already
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gives us the bytesperline / sizes the driver chose; nothing else
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in this file consumed the explicit S_FMT side-effects.
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Empirical hypothesis test for the lingering "kernel decodes
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without errors but emits zeroed CAPTURE" bug. If post-patch
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output shows actual picture content, this confirms the
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diagnosis: explicit CAPTURE format mutation breaks hantro's
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internal state. If output remains flat-green, the bug is
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elsewhere and we resume hex-dump-grade instrumentation.
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Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>
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---
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--- a/src/surface.c 2026-05-01 21:16:19.588759711 +0000
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+++ b/src/surface.c 2026-05-01 21:41:12.095146549 +0000
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@@ -118,10 +118,20 @@
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capture_type = v4l2_type_video_capture(video_format->v4l2_mplane);
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- rc = v4l2_set_format(driver_data->video_fd, capture_type,
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- video_format->v4l2_format, width, height);
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- if (rc < 0)
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- return VA_STATUS_ERROR_OPERATION_FAILED;
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+ /*
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+ * Do not VIDIOC_S_FMT on the CAPTURE queue. The hantro
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+ * stateless decoder derives the CAPTURE format from the
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+ * SPS attached to the OUTPUT request; explicitly setting
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+ * it here can put the driver into an inconsistent state.
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+ * GStreamer's v4l2slh264dec only G_FMTs CAPTURE (see
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+ * gst-plugins-bad/sys/v4l2codecs/gstv4l2decoder.c::
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+ * gst_v4l2_decoder_negotiate_src_format), and that
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+ * variant produces correct decoded NV12 on the same
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+ * hardware where this driver currently emits zeros.
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+ *
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+ * v4l2_get_format() below queries the driver's current
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+ * state and gives us the bytesperline/sizes we need.
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+ */
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} else {
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video_format = driver_data->video_format;
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capture_type = v4l2_type_video_capture(video_format->v4l2_mplane);
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