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| fourier:journey [2026/04/28 22:06] – fourier: chronological journey (chromium -> qt6 -> kwin -> capture pool -> RFC) markus_fritsche | fourier:journey [2026/04/29 04:16] (current) – fix HTML-entity over-escape (' -> ' ; " -> "); restores monospace markup markus_fritsche |
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| Chronological account of how a single-patch chromium V4L2 dispatch | Chronological account of how a single-patch chromium V4L2 dispatch |
| unlock turned into a 4-series + RFC + 3 upstream draft campaign. | unlock turned into a 4-series + RFC + 3 upstream draft campaign. |
| Each step uncovered the next layer's contributing bug. | Each step uncovered the next layer's contributing bug. |
| Index: [[fourier:start]]. | Index: [[fourier:start]]. |
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| ===== The cascade ===== | ===== The cascade ===== |
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| - **Started as a single chromium V4L2 dispatch unlock** — flip ''kAcceleratedVideoDecodeLinux'' default + re-allow direct EGL/GLES2 in ''WaylandSurfaceFactory''. Two patches, "does it decode?". | - **Started as a single chromium V4L2 dispatch unlock** — flip ''kAcceleratedVideoDecodeLinux'' default + re-allow direct EGL/GLES2 in ''WaylandSurfaceFactory''. Two patches, "does it decode?". |
| - **Discovered every NV12 modifier on panfrost is ''external_only''** → wrote chromium patch 3 (NV12 ''EXTERNAL_OES''). Without this, sampling NV12 from a panfrost dmabuf goes through a path that doesn't advertise the modifier correctly. | - **Discovered every NV12 modifier on panfrost is ''external_only''** → wrote chromium patch 3 (NV12 ''EXTERNAL_OES''). Without this, sampling NV12 from a panfrost dmabuf goes through a path that doesn't advertise the modifier correctly. |
| - **Validated patch 3** → discovered chrome stalled at 3 s under KWin. Different bug, deeper layer. | - **Validated patch 3** → discovered chrome stalled at 3 s under KWin. Different bug, deeper layer. |
| - **Attributed stall to Qt 6 ''glTexImage2D(GL_ALPHA)'' errors** — ''GL_ALPHA'' is deprecated as an internalFormat in OpenGL ES 3.0; Qt 6 was hard-coding it via ''QT_CONFIG(opengles2)'' with no runtime ES check. Wrote **qt6-base-fourier** (3 patches). | - **Attributed stall to Qt 6 ''glTexImage2D(GL_ALPHA)'' errors** — ''GL_ALPHA'' is deprecated as an internalFormat in OpenGL ES 3.0; Qt 6 was hard-coding it via ''QT_CONFIG(opengles2)'' with no runtime ES check. Wrote **qt6-base-fourier** (3 patches). |
| - **Stall persisted at 6 s** → identified KWin's ''Transaction::watchDmaBuf'' parking transactions on stub fences. The compositor was waiting for a fence the producer never signalled. | - **Stall persisted at 6 s** → identified KWin's ''Transaction::watchDmaBuf'' parking transactions on stub fences. The compositor was waiting for a fence the producer never signalled. |
| - **Wrote kwin-fourier 0001** (diagnostic bypass) → stall persisted at 22 s → identified the V4L2 capture pool depth equal to chrome's pipeline depth. Decoder running, compositor working, but the pipeline deadlocked itself on buffer count. | - **Wrote kwin-fourier 0001** (diagnostic bypass) → stall persisted at 22 s → identified the V4L2 capture pool depth equal to chrome's pipeline depth. Decoder running, compositor working, but the pipeline deadlocked itself on buffer count. |
| - **Wrote chromium patch 4** (capture pool floor at 16) → **end-to-end smooth playback** on ohm. ~81 % chrome CPU vs ~131 % pre-patch baseline. | - **Wrote chromium patch 4** (capture pool floor at 16) → **end-to-end smooth playback** on ohm. ~81 % chrome CPU vs ~131 % pre-patch baseline. |
| - **Drafted upstream-shape kwin patch 0002** (poll dmabuf fd directly instead of going through ''EXPORT_SYNC_FILE'' + ''QSocketNotifier''), **vb2-dma-resv RFC** (3-patch kernel series — the architectural correction that makes the kwin wait premise actually true), and the **Qt 6 bug report** body. | - **Drafted upstream-shape kwin patch 0002** (poll dmabuf fd directly instead of going through ''EXPORT_SYNC_FILE'' + ''QSocketNotifier''), **vb2-dma-resv RFC** (3-patch kernel series — the architectural correction that makes the kwin wait premise actually true), and the **Qt 6 bug report** body. |
| - **Restructured public github repo** from ''chromium-fourier'' → ''fourier'' with sibling subdirs (''chromium-fourier/'', ''qt6-base-fourier/'', ''kwin-fourier/'', ''docs/'', ''tools/''). The campaign needed a name that reflected what it actually was. | - **Restructured public github repo** from ''chromium-fourier'' → ''fourier'' with sibling subdirs (''chromium-fourier/'', ''qt6-base-fourier/'', ''kwin-fourier/'', ''docs/'', ''tools/''). The campaign needed a name that reflected what it actually was. |
| - **Mesa ''Syyuu'' regression on fresnel** diagnosed and worked around — mesa 26.0.5 introduced a panfrost GLX regression on Mali-T860 that crashes ''sddm-greeter-qt6''. Pinned to 26.0.3 via ''IgnorePkg''. **Separate from fourier work,** captured here because it surfaced during a fresnel install of fourier packages. | - **Mesa ''Syyuu'' regression on fresnel** diagnosed and worked around — mesa 26.0.5 introduced a panfrost GLX regression on Mali-T860 that crashes ''sddm-greeter-qt6''. Pinned to 26.0.3 via ''IgnorePkg''. **Separate from fourier work,** captured here because it surfaced during a fresnel install of fourier packages. |
| - **firefox-fourier patch 3 runtime defect identified and corrected** (today, 2026-04-28; rebuild pending on boltzmann). ''MOZ_LOG'' showed patch 3 only walked the generic codec's ''hw_configs''; libavcodec on ALARM registers v4l2_request as separate ''AVCodec'' entries (''h264_v4l2request'' etc.). Corrected to probe by name first, fall back to ''hw_configs''. | - **firefox-fourier patch 3 runtime defect identified and corrected** (today, 2026-04-28; rebuild pending on boltzmann). ''MOZ_LOG'' showed patch 3 only walked the generic codec's ''hw_configs''; libavcodec on ALARM registers v4l2_request as separate ''AVCodec'' entries (''h264_v4l2request'' etc.). Corrected to probe by name first, fall back to ''hw_configs''. |
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| ===== Source-of-truth narratives ===== | ===== Source-of-truth narratives ===== |
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| The investigation thread is documented in ''[[https://git.reauktion.de/marfrit/marfrit-packages|gitea/marfrit-packages]]'' under: | The investigation thread is documented in ''[[https://git.reauktion.de/marfrit/marfrit-packages|gitea/marfrit-packages]]'' under: |
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| * ''arch/chromium-fourier/NEXT.md'' — campaign chronology, including the 2026-04-28 closing section | * ''arch/chromium-fourier/NEXT.md'' — campaign chronology, including the 2026-04-28 closing section |
| * ''arch/chromium-fourier/KWIN_PIVOT.md'' — the discovery story for the qt6 + kwin layers | * ''arch/chromium-fourier/KWIN_PIVOT.md'' — the discovery story for the qt6 + kwin layers |
| * ''docs/dmabuf-zero-copy.md'' (in github.com/marfrit/fourier) — the panfrost ''external_only'' finding and how it cascaded into chromium patches 2 + 3 | * ''docs/dmabuf-zero-copy.md'' (in github.com/marfrit/fourier) — the panfrost ''external_only'' finding and how it cascaded into chromium patches 2 + 3 |
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| ===== Pattern ===== | ===== Pattern ===== |
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| > //Every time a layer was patched, the next layer's contributing bug surfaced. The campaign was over when **all four layers** (chromium, Qt 6, KWin, the V4L2 capture pool depth) were patched on the same machine, on the same kernel, on the same compositor.// | > //Every time a layer was patched, the next layer's contributing bug surfaced. The campaign was over when **all four layers** (chromium, Qt 6, KWin, the V4L2 capture pool depth) were patched on the same machine, on the same kernel, on the same compositor.// |
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| The vb2-dma-resv RFC is the only piece that adjusts a fifth layer (the | The vb2-dma-resv RFC is the only piece that adjusts a fifth layer (the |
| kernel video producer), and it's a //correctness// patch rather than a | kernel video producer), and it's a //correctness// patch rather than a |
| gating one — kwin-fourier 0002 already works without it; the RFC just | gating one — kwin-fourier 0002 already works without it; the RFC just |
| removes the need for the workaround. | removes the need for the workaround. |
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