Phase 3 strace + byte-level analysis on fresnel rkvdec. Findings:
1. Bug 4 is NOT inter-race-loss. The IDR keyframe itself fails through
libva (only 512 bytes of real Y data at top-left 16x32 region).
2. The 16x32 leak is structured real image content (smooth gradients,
neutral luma ~0x80) — kernel decoded one tile / one MB pair, then
stopped.
3. VP9 via libva WORKS through the same readback path (100% non-zero,
real image data). So the bug isn't generic DMA-BUF cache coherency.
4. HEVC fails via libva (all-zero, distinct from H.264 partial-fill).
5. OUTPUT sizeimage = 1MB (SOURCE_SIZE_MAX) is sufficient — BBB IDR is
only 6321 bytes. Not the bug.
6. Control payload diffs: SPS.constraint_set_flags = 0 vs kdirect's 2
(probably cosmetic); DECODE_PARAMS.dpb[0].bottom_field_order_cnt = 0
vs kdirect's 1 (load-bearing for POC).
Refined hypothesis: a specific H.264 control field libva sends causes
rkvdec to abort after partial decode. Phase 4 candidates: α fix POC
fields, β bump OUTPUT sizeimage, γ instrumentation dump, δ relative
timestamps.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
