# x11-session-research

> **Status: PHASE 0 — motivation locked 2026-05-03.**
> See [`phase0_findings.md`](phase0_findings.md) §
> "Research question (LOCKED 2026-05-03)". Phase 1 still
> requires the four pre-question Phase 0 deliverables
> (state snapshot, X11 path inventory, browser-overlay-path
> inventory, baseline anchor) before binding cells lock.

**Research question:** Does cutting out the KWin compositor
enable faster video display of Brave, chromium-fourier, and
Firefox — for full SW decoding, and for libva decoding (where
possible) — on PineTab2 RK3568?

The operator-supplied mechanism: hantro decodes to NV12;
rockchip-drm's overlay plane cannot accept NV12, so on Wayland
KWin must own the only NV12-capable plane (Primary, Plane 39)
for its compositor framebuffer, which forces a GL-composite
of every NV12 video buffer. X11 + non-compositing WM can give
the video region directly to Plane 39 (NV12 native) and put
the rest of the desktop on Plane 45 (RGB AFBC), avoiding the
forced GL-composite. **The campaign's load-bearing hypothesis
is that this plane-allocation freedom translates into
measurable browser-video speedup.**

The matrix is 3 browsers × 2 decode paths × 2 sessions = 12
cells (some N/A where libva isn't supported). See
`phase0_findings.md` for the full table.

## Predecessor

This campaign exists because
[`../kwin_overlay_subsurface/`](../kwin_overlay_subsurface/)
closed 2026-05-03 without patch (`phase8_handover.md`). Its
diagnostic loop terminated at "Phase 0 cage = 0 post-warmup
drops floor not reproducible at N=3." The natural next move
across the design surface is to vary the display server (X11
instead of Wayland) on the same hardware and the same client
binary, but the operator has not yet confirmed that as the
campaign's specific question.

## Hardware target (provisional, same as predecessor)

ohm — PineTab2, Rockchip RK3568 (4× Cortex-A55, Mali-G52 MP2,
hantro G1/G2 VPU). Kernel `6.19.10-danctnix1-1-pinetab2`.
Mesa 26.0.5. Currently runs KDE Plasma 6.6.4 Wayland.

For an X11-session campaign, ohm needs an Xorg + Plasma X11 (or
similar X11 desktop) install path verified. As of 2026-05-03,
the only confirmed display path on ohm is
`startplasma-wayland`. **Whether Plasma X11, an alternate X11
desktop (XFCE, openbox, lightweight WM), or Plasma running
under a Wayland-Xorg shim is in scope is part of the research
question to be locked.**

## Carry-overs from predecessor (still active on ohm)

Per `kwin_overlay_subsurface/phase1_evidence/ohm_tooling_revert_log.md`:

- `qt6-base-fourier 1:6.11.0-3` installed.
- `kwin-fourier 1:6.6.4-3` installed.
- CPU governor pinned to `performance` (was `conservative`).
- Baloo permanently disabled
  (`Indexing-Enabled=false` in `~/.config/baloofilerc`).
- `drm-info 2.9.0-1` installed.

These were not reverted at the predecessor's close-out. This
campaign inherits them unless an explicit revert is part of
the design.

## Non-upstreaming default

Inherited from the predecessor and from `ohm_gl_fix`. Bug
reports + MRs are explicit operator-tasked decisions, not
background process steps.

## File map (will grow)

| File | What it is |
|---|---|
| `README.md` | This file. |
| `phase0_findings.md` | Substrate from the predecessor + the candidate research question. **Awaits operator confirmation/redirect on the question itself.** |
| `worklist.md` | Phase-by-phase task list. Phase 0 only as of campaign start. |