# Phase 2 close — VP9 backend compiles clean

Date: 2026-05-17 ~02:55. Phase 2 (`Implement rkvdec-vdpu381-vp9.c backend`) closed at the "compiles clean against 7.0.0-rc3 ARM64 kernel" milestone.

## Three commits on `boltzmann:~/src/linux-rockchip` branch `vp9-enablement-iter1`

| Commit | Subject | LoC |
|---|---|---|
| `47431635801d` | media: rkvdec: Add VP9 register-struct definitions for VDPU381 variant | +238 |
| `da8482271938` | media: rkvdec: Add shared VP9 codec-spec helpers in rkvdec-vp9-common.h | +511 |
| `71cc0d96d212` | media: rkvdec: Add VP9 backend for VDPU381 variant (RK3588) | +513 |

Total: +1262 lines across 4 files. The vdpu381-hevc reference (Casanova v7.0) is 639 lines; Phase 1 estimated VP9 backend at 550-700; we landed at 513 backend + 511 common-header = within range.

## Build verification

```
boltzmann$ cd ~/src/linux-rockchip
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
```

Zero errors, zero warnings on the new file after fixing two field-name typos caught by the compiler:

| Bug | Fix |
|---|---|
| Used BSP-style `reg128_rlc_base` / `reg130_decout_base` / `reg131_colmv_cur_base` for `struct rkvdec_vdpu381_regs_common_addr` fields | Mainline naming is plain `rlc_base` / `decout_base` / `colmv_cur_base`; corrected |
| Unused variable `i` in `vdpu381_config_vp9_regs` | Removed |

These both are pre-flash compiler-caught bugs of exactly the kind Janet predicted in v2 review re. namespace bridging — the legacy `regs->common.reg02.dec_mode` style is muscle-memory from reading the legacy file. Corrected without regression.

## What's NOT yet correct (deferred TODOs in the backend file)

5 `TODO Phase 2.1` markers in `vdpu381_config_vp9_regs` for fields that compile fine but aren't yet packed correctly. These will be needed for first-light decode but the skeleton is structurally correct:

1. RCB address setup (`common_addr.rcb_base[10]` — currently NULL; needs `vdpu381_set_rcb_addrs` equivalent to HEVC path)
2. Segmentation register packing per `segid 0..7` (`reg067_074_segid[]` — currently zero-init; needs `config_seg_registers` port)
3. Loop-filter `ref_deltas[0..3]` bit-pack into `reg094_ref_deltas_lastframe.ref_deltas_lastframe` (28-bit field combining 4× 7-bit deltas)
4. Loop-filter `mode_deltas[0..1]` bit-pack into `reg075_last_frame_info.mode_deltas_lastframe` (14-bit field)
5. Probability storage rotation: `reg160_delta_prob_base`, `reg162_last_prob_base`, `reg172_update_prob_wr_base` (per BSP `Vdpu382Vp9dCtx_t::prob_idx` cycle logic)

## Open questions surfaced during Phase 2 implementation

| Q | Question | Status |
|---|---|---|
| C-1 | `reg103_frame_flags` extra bits (`prob_update_en`, `txfmmode_rfsh_en`, etc.) — required for first decode? | Hypothesis: only the most-obviously-needed bits set (intra_only, refresh_en, allow_high_precision_mv, interp_filter_switch_en); others left zero — verify empirically |
| C-2 | `reg160_delta_prob_base` and `reg162_last_prob_base` — new DMA allocations or alias existing? | Hypothesis: alias `priv_tbl.probs` regions; verify against BSP `vdpu382_set_vp9d_buffer` equivalent |
| C-3 | `reg028.vp9_rd_prob_idx`/`vp9_wr_prob_idx` first-frame values? | Currently both = 0 in skeleton. BSP rotates; will need iteration |
| C-4 | RCB write-out — does mainline `rkvdec_setup_rcb` already populate `common_addr.rcb_base[]`, or does each backend need to wire it? | HEVC backend (`rkvdec-vdpu381-hevc.c:362-374`) writes RCB addrs explicitly. Mirror that pattern in VP9 backend |
| C-5 | `reg032_timeout_threshold` — set to RKVDEC_TIMEOUT_4K (0x2cfffff) for 4K-max VP9? | Yes; add to register setup |

## Push status

`git push gitea vp9-enablement-iter1` from boltzmann is hanging (ssh timeout). Commits are safely on boltzmann disk in branch `vp9-enablement-iter1`. Will retry push next session. Branch will eventually land at `git.reauktion.de/marfrit/linux-rk3588-marfrit:vp9-enablement-iter1`.

## What Phase 3 needs (next-session entry point)

1. **Retry push** to gitea from boltzmann to back up the work off-disk.
2. **Implement the 5 TODOs** in `vdpu381_config_vp9_regs`. Each is a 5-15 line bit-packing task referencing the BSP `hal_vp9d_vdpu382.c` source. Expect ~100-200 LoC delta.
3. **Build module + backup ampere's current rockchip-vdec.ko** per [feedback_backup_before_module_replace](../../.claude/projects/-home-mfritsche-src-fresnel-fourier/memory/feedback_backup_before_module_replace.md) before install.
4. **Install + modprobe cycle** — `scp boltzmann:~/src/linux-rockchip/drivers/media/platform/rockchip/rkvdec/rockchip-vdec.ko ampere:/lib/modules/7.0.0-rc3-devices+/kernel/drivers/media/platform/rockchip/rkvdec/`, then `ssh ampere "sudo modprobe -r rockchip-vdec && sudo modprobe rockchip-vdec"`.
5. **Sanity enumeration**: `v4l2-ctl --device=/dev/video0 --list-formats-out` should show VP9F alongside H264_SLICE and HEVC_SLICE.
6. **Pre-flight diagnostic**: instrument `vdpu381_irq_handler` with `pr_warn("vp9 irq status=0x%x\n", status)` for first 5 decodes (per Janet Amendment C) to verify IRQ status bit semantics before counting on `VDPU381_STA_INT_DEC_RDY_STA = BIT(2)`.
7. **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`. Watch dmesg for IRQ status. Most likely outcome on first attempt with TODO #1-5 unresolved: watchdog 2-second timeout (no decode complete IRQ).
8. **Iterate** on the TODOs until first-light. Then SW byte-compare on a non-fade-in frame index.

## Persistence checkpoint

- **Campaign repo**: 4 commits at `git.reauktion.de/claude-noether/ampere-vp9-enablement` master (phase0, phase1, phase1_v2, phase1_v3_amendment, phase2_field_mapping, this doc).
- **Kernel branch**: 3 commits on `boltzmann:~/src/linux-rockchip:vp9-enablement-iter1` (not yet pushed to gitea due to ssh timeout).
- **Module artifact**: `boltzmann:~/src/linux-rockchip/drivers/media/platform/rockchip/rkvdec/rockchip-vdec.ko` (compiled, NOT yet installed on ampere).
- **No ampere changes**: ampere is still on sibling-campaign close state (HEVC bit-perfect, iter3+iter4 kernel patches in modules).
- **Rockchip BSP reference**: `boltzmann:~/src/rockchip-bsp/{mpp,rk-kernel-6.6}` — clones retained for Phase 3 cross-reference of `Vdpu382Vp9dCtx_t::prob_idx` rotation and RCB setup.

Phase 2 closes here. Substantial code artifact in hand; remaining bit-level field translation is well-scoped (5 TODOs, all with BSP reference locations identified) for the next session.