diff --git a/phase2_1_close.md b/phase2_1_close.md
new file mode 100644
index 0000000..49e9e9f
--- /dev/null
+++ b/phase2_1_close.md
@@ -0,0 +1,63 @@
+# Phase 2.1 close — 5 register-packing TODOs implemented
+
+Date: 2026-05-17 ~03:10. Phase 2.1 closed in the same session as Phase 2 — module builds clean with the full register-packing path.
+
+## Commit on `boltzmann:~/src/linux-rockchip:vp9-enablement-iter1`
+
+`63c4db0095ca` — media: rkvdec: VP9 (vdpu381): implement Phase 2.1 register-packing TODOs (+128, -10)
+
+Stacks on Phase 2's 3 commits (`47431635801d`, `da8482271938`, `71cc0d96d212`). Total branch delta now 1390 LoC across 4 files.
+
+## What changed
+
+| TODO | Implementation |
+|---|---|
+| 1. RCB addresses | `for (i = 0; i < rkvdec_rcb_buf_count(ctx); i++) regs->common_addr.rcb_base[i] = rkvdec_rcb_buf_dma_addr(ctx, i);` — direct mirror of vdpu381-HEVC pattern |
+| 2. Block clock-gating defaults | All `reg026_block_gating_en.*` fields set from HEVC defaults (busifd_auto_gating_e = 0 per pattern, rest = 1) |
+| 3. Frame-area timeout threshold | RKVDEC_TIMEOUT_1080p/_4K/_8K/_MAX based on pixel count; `rkvdec_schedule_watchdog()` replaces the fixed 2-second `schedule_delayed_work` |
+| 4. Seg-register packing | `vdpu381_config_seg_register(vp9_ctx, segid)` helper called 8× — full port of legacy `config_seg_registers` to `reg067_074_segid[]` |
+| 5. Loop-filter bit-packing | `ref_deltas[0..3]` → 28-bit packed into `reg094.ref_deltas_lastframe`; `mode_deltas[0..1]` → 14-bit packed into `reg075.mode_deltas_lastframe` (using `(x & 0x7f) << (i*7)`) |
+| Bonus: probability storage | `reg160_delta_prob_base`, `reg162_last_prob_base`, `reg172_update_prob_wr_base` aliased to `priv_tbl.probs` for first-cut; per-slot rotation deferred to Phase 6 if adaptive entropy diverges |
+| Bonus: prob_idx | `reg028.vp9_rd_prob_idx = vp9_wr_prob_idx = 0` first-cut; BSP rotates across frames |
+
+## Build verification
+
+```
+boltzmann$ PATH=/home/mfritsche/bin:$PATH make -j$(nproc) \
+    ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- \
+    drivers/media/platform/rockchip/rkvdec/
+
+  CC [M]  drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu381-vp9.o
+  LD [M]  drivers/media/platform/rockchip/rkvdec/rockchip-vdec.o
+```
+
+Clean — zero warnings, zero errors.
+
+## What remains potentially-needed for first-light decode
+
+| Field | Risk | Mitigation |
+|---|---|---|
+| `reg103_frame_flags.txfmmode_rfsh_en`, `ref_mode_rfsh_en`, `single_ref_rfsh_en`, `comp_ref_rfsh_en`, `inter_coef_rfsh_flag`, `last_key_frame_flag`, `prob_update_en`, `prob_save_en` | Frame may decode but adaptive entropy may diverge from SW after a few frames | Currently zero-init. Verify via byte-compare on frames 1-5 vs SW reference. If divergence, mirror BSP `vp9d_vdpu382_gen_regs` setting logic |
+| Probability slot rotation | First-cut single-slot may corrupt frame_context across multiple inter frames | Watch dmesg + byte-compare frames 2+ vs SW reference |
+| RCB sizing | HEVC-tuned for 8K, oversized for 4K VP9 | Wastes SRAM but doesn't fail; tune in Phase 6 |
+
+## Phase 3 entry point (unchanged, hardware-domain)
+
+Phase 3 needs hardware:
+1. Retry `git push gitea vp9-enablement-iter1` (or push `linux-rk3588-marfrit` base first)
+2. Backup ampere's current `/lib/modules/7.0.0-rc3-devices+/kernel/drivers/media/platform/rockchip/rkvdec/rockchip-vdec.ko` (with off-device archive per [feedback_backup_before_module_replace](../../.claude/projects/-home-mfritsche-src-fresnel-fourier/memory/feedback_backup_before_module_replace.md))
+3. `scp` boltzmann's `rockchip-vdec.ko` to ampere; `modprobe -r/modprobe` cycle (no reboot needed — kernel decoder module hot-swappable)
+4. Sanity: `v4l2-ctl --device=/dev/video0 --list-formats-out` shows `VP9F` alongside H264_SLICE + HEVC_SLICE
+5. Pre-flight IRQ diagnostic: `pr_warn("vp9 irq status=0x%x\n", status)` in `vdpu381_irq_handler` for first 5 decodes (Janet Amendment C)
+6. First decode attempt: `LIBVA_DRIVER_NAME=v4l2_request ffmpeg -hwaccel vaapi -i bbb_30s_720p.vp9.webm -vf hwdownload,format=nv12 -frames:v 5 -f rawvideo /tmp/hw-vp9.nv12`
+7. Watch dmesg for IRQ status, watchdog firing, error patterns
+8. If first-light works: SW byte-compare on frame 100 against `ffmpeg -c:v vp9` reference
+
+## Tonight's campaign summary
+
+Started: ampere-vp9-enablement campaign opened at ~01:00, sibling to ampere-kernel-decoders close.
+Closed: 4 commits on branch + 7 docs in campaign repo, module compiles clean on RK3588 target kernel.
+
+Wall-time: ~2h15m for Phase 0 (substrate) + Phase 1 (plan + 2 architect reviews) + Phase 2 (1400 LoC implementation) + Phase 2.1 (full register-packing). All architecturally-correct work; bit-level register correctness verified next session against hardware.
+
+Next session continues at the hardware testing inflection point.