Replace the hand-rolled draft patches with the proper
git-format-patch output. The new files apply cleanly via git am
against unmodified Linux 6.12 mainline, verified by reset-and-apply
roundtrip on /tmp/hantro-src (the local sparse checkout used during
the chromium-fourier campaign).
All kernel API calls also sanity-checked against the real
include/linux/dma-fence.h and include/linux/dma-resv.h signatures:
- dma_fence_init(fence, ops, lock, context, seqno) — argument list
matches our call exactly
- dma_resv_add_fence(obj, fence, usage) — DMA_RESV_USAGE_WRITE
enum value confirmed present
- dma_fence_signal, dma_fence_set_error, dma_fence_get,
dma_fence_put, dma_fence_context_alloc — all present and
correctly used
- dma_resv_lock(obj, NULL), dma_resv_unlock — present, correctly
paired
README updated to reflect the post-verification status. Remaining
gates before sending to linux-media are now: full-tree compile
test (needs complete kernel checkout, hours of work), boot test on
ohm (needs patched kernel build), and the runtime A/B (install
patched kernel + uninstall kwin-fourier — chrome should still play
1080p30 because the fence is now real).
Cover letter blurb filled in with the full motivation, test setup,
and review-question list.
Drafted but not yet compile-tested or runtime-validated. Draft
target: vb2 grows an opt-in dma_resv release-fence API; hantro and
rockchip-rga opt in as the demonstration drivers.
Series structure:
- 0000-cover-letter.patch — context, motivation, validation results
- 0001-media-videobuf2-add-dma_resv-release-fence-helper.patch
Adds vb2_buffer_attach_release_fence() that drivers call from
their buf_queue callback. Stores the fence on vb->release_fence;
vb2_buffer_done signals + puts. Per-queue fence context allocated
at vb2_core_queue_init.
- 0002-media-hantro-attach-dma_resv-release-fence-at-buf_queue.patch
Single call in hantro_buf_queue. ~5 lines.
- 0003-media-rockchip-rga-attach-dma_resv-release-fence-at-buf_queue.patch
Same shape in rga_buf_queue. ~5 lines.
Pre-flight before sending to linux-media (per kernel/README.md):
1. Compile the touched files against the kernel tree the patches
will land on (linux-next master as of 2026-04-28 was the source
of truth used for context-line generation).
2. Boot-test on ohm, smoke-test hantro + rga buffer flows.
3. Validate the fence semantics: install patched kernel, uninstall
kwin-fourier so KWin's watchDmaBuf is active, play 1080p30 H.264
under KDE Plasma — should plays through without the bypass
because the fence is now real.
4. Capture before/after dma_buf_export_sync_file timings.
5. Send via git format-patch --cover-letter to linux-media@,
CC dri-devel@ and the relevant maintainers.
This series is the kernel-correct fix for the architectural hole
that the chromium-fourier campaign's kwin-fourier package is
papering over. With this kernel side upstream, kwin-fourier
becomes either redundant (if KWin's existing wait works correctly)
or rewritten as a poll-fd-direct optimization.
marfrit