POWER-FINAL-40 — handover snapshot for the restart display defect
Status: SEALED, awaiting the owner flash (2026-10-15). Package out/y2linux-platform-v1-power-final-candidate-40/ (fallback = 39), receipts out/deep-sleep-final/build40-receipts/. BOOTIMG bc44a93d183ea980a4755eef95f0b935dbd491a86084eda1d87c93870d68d503, Y2ROOT 37198d908a7e3fc99265e227f596993dfd2e2ed9b543cfd64e42d900cfd6392d, RECOVERY ad06315e34500c6a33d90f8d6e81867d5c03409a12cdec57c2d6fac8de16d1f6. Kernel 6.18.56-y2linux-platform-v1-power-final-40, release …candidate.40, update sequence 4000. Container suite 718 OK, all seal checks PASS. Diagnostic only; contains 39.
Why
After a software restart SMI larb0 reads busy (39, archives 137/138), also when the display was stopped before the restart. Unknown: is larb0 already busy when Linux takes over LK's pipeline, or does our handover wedge it?
| Change | Detail |
|---|---|
| Handover snapshots | /sys/kernel/debug/y2_display_snapshot slots 2 (handover, DSI probe before Linux touches LK's live pipeline) and 3 (parked), first probe of the boot only; larb0 0x400–0x4fc added. |
| Log | handoff: snapshot … and handoff: parked … with larb0 stat/greq, OVL status, OVL RDMA0, RDMA irq. |
Device results — root cause found
Cold start (archive 20261016/139) and one software restart (archive 140, panel dark). At **handover, before Linux touches anything** (slot 2), the restart differs from the cold start in exactly the way that explains the defect:
| Register | Cold | Restart |
|---|---|---|
MMSYS_CG_CON0 (0x14000100) | 0 | 1 — SMI common clock gated |
| SMI common config (0x14011200/228/230/234/300/404) | configured | 0 (gated block reads zero) |
| larb0 status / GREQ (0x14010000 / 0x450) | 0 / 0 | 1 / 1 — request pending |
| OVL status | 0x1e | 0x1f (still running) |
Linux gates SMI common when the display and GPU release it at shutdown; the watchdog restart keeps MMSYS_CG_CON0; LK assumes the cold default, shows its logo, and its first fetch through larb0 never completes. Every later symptom (full OVL FIFO, no RDMA frame, no vblank, mutex timeout) follows. 38's external reset and 39's mutex reset could not help. Fix: POWER-FINAL-41.
Owner steps
- Flash 40 (BOOTIMG + ANDROID). Cold start: the agent saves the snapshots.
- With the owner's OK: one software restart; the panel will likely stay dark. The agent saves the snapshots, then
the owner holds Power 10 s. Diff cold/warm at
handoverandparked.