# iter22 — maxImageDimension3D bump for Dawn/WebGPU (campaign close)

Shipped: 2026-05-25
PR: https://git.reauktion.de/marfrit/marfrit-packages/pulls/103
Merge commit: 520f2fce337d
Package: `mesa-panvk-bifrost-26.0.6.r9-1-aarch64`

## What shipped

Two-hunk patch (`0008-panvk-bifrost-bump-max-image-dim-3d-for-dawn.patch`):

1. **Bump `maxImageDimension3D` from 512 to 2048** on Bifrost (PAN_ARCH 7..10).
   File: `src/panfrost/vulkan/panvk_vX_physical_device.c:651`.
2. **Remove three wrong-invariant asserts** in `get_max_3d_image_size()`
   (`src/panfrost/vulkan/panvk_physical_device.c:1018-1020`) that encoded
   "per-format max >= basic limit" — the opposite of what the Vulkan spec
   mandates.

## How surfaced

panvk-bifrost-perf-measurement iter1 spike (task #98) was setting up an
A/B MotionMark test of stock GL vs panvk Vulkan in Brave. The spike
showed that Brave's WebGPU/Dawn **detects** our shipped r7 driver as a
valid Vulkan adapter:

```
Mali-G52 r1 MC1 - panvk: Mesa 26.0.6
  vendorId=0x13b5 deviceId=0x74021000
  backend=BackendType::Vulkan type=AdapterType::IntegratedGPU
```

But **immediately rejects** it:

```
Warning: Insufficient Vulkan limits for maxTextureDimension3D.
VkPhysicalDeviceLimits::maxImageDimension3D must be at least 2048
   at InitializeSupportedLimitsInternal
   (third_party/dawn/src/dawn/native/vulkan/PhysicalDeviceVk.cpp:746)
```

The perf measurement was premature — there was no point comparing
MotionMark scores if Dawn refused to use the panvk adapter in the
first place. r9 was the actual unblock for the **campaign's stated
motivator** (Chromium GPU process Vulkan boot on PineTab2 / Bifrost
SBCs).

## Why both hunks

Phase 5 (2nd-model) review caught a release-mode-masked semantic bug:
the three asserts in `get_max_3d_image_size()` encoded the wrong
invariant. The shipped `b_ndebug=if-release` build no-ops them, but
debug builds (CTS, devs running meson defaults) would abort the first
time Dawn called `vkGetPhysicalDeviceImageFormatProperties(3D, format)`
post-r9. Hunk 2 removes them.

## Verification

| Check                                                | Result |
|------------------------------------------------------|--------|
| vulkaninfo: maxImageDimension3D                      | **2048** (was 512) |
| Brave/Dawn: "Insufficient" warning                   | **eliminated** |
| `dEQP-VK.api.copy_and_blit.core.image_to_image.3d_images.*` | 6/6 Pass (unchanged) |
| Phase 5 2nd-model review                             | APPROVE WITH CHANGES — both applied |

## Three-point ship-check verdict

1. ✓ PR #103 merged at `520f2fce337d`
2. ✓ CI runs #1486 (`mesa-panvk-bifrost-aarch64`) + #1487 (`mesa-panvk-bifrost-video-aarch64`) both success
3. ✓ `pacman -Q mesa-panvk-bifrost` on ohm reports `26.0.6.r9-1`; installed lib BuildID `63911eae...`; vulkaninfo confirms 2048; Brave headless mode produces standard non-conformant warnings only — no Dawn rejection.

## Why not bump max_img_size_B too?

The current `arch <= 10 ? u_uintN_max(32)` (4 GB) caps the per-format
runtime limit at ~1023 per axis for RGBA8. We could bump to
`u_uintN_max(48)` to widen the address space and let larger per-format
3D images actually be creatable. **But** that requires HW evidence
that the Bifrost MMU + kernel driver actually handle 48-bit image
offsets, which is uncertain pre-CSF. Held for a future iter with HW
probing.

## Open follow-ups

- **panvk-bifrost-perf-measurement iter2** — re-do the MotionMark
  A/B now that Dawn accepts the adapter. The original task #98 close
  doc was preempted by this finding; iter2 would actually capture the
  comparison numbers.
- **Brave / Chromium GPU process** real-world testing — confirm in
  windowed mode (not headless) that the GPU process boots with our
  Vulkan path and renders without falling back.

## Lineage

| rev | What                                          | Date       |
|-----|-----------------------------------------------|------------|
| r1  | KHR_robustness2 + nullDescriptor on Bifrost   | iter8      |
| r2  | has_vk1_1/has_vk1_2 = true on Bifrost         | iter9      |
| r3  | VK_EXT_transform_feedback                     | iter13     |
| r4  | XFB primitive decomposition                   | iter17     |
| r5  | fragmentStoresAndAtomics = true               | 2026-05-23 |
| r6  | VK_EXT_legacy_dithering                       | 2026-05-25 |
| r7  | XFB packed-varying channel-extract fix        | 2026-05-25 |
| (r8) | KHR_depth_clamp_zero_one trim — abandoned    | 2026-05-25 |
| **r9** | **maxImageDimension3D = 2048 for Dawn**     | **2026-05-25** |