marfrit
a4e7d8ab90
panvk-bifrost campaigns (r1..r4 Vulkan compositor + r5.video1 Vulkan
video decode) shipped before this repo existed; the deliverable
patches live in marfrit-packages, but the reasoning chain, phase docs,
and source-state evidence lived only in local working trees on the
development host.
This retrofit imports:
- mesa-panvk-bifrost/ — r1..r4 era phase docs (iter1..iter18)
(libmali stub blobs at iter18/blob/ excluded
— 109MB of RE artifacts replaced with a README
pointer)
- mesa-panvk-bifrost-video/ — sibling campaign phase docs + probe
- evidence/ — frozen .tgz source snapshots at each milestone
(basis for the 0005 patch diff generation)
Future iterations should branch off here from day one, so each iter is
a commit rather than a snapshot. See [[feedback-session-local-process-pins]]
for the process drift this retrofit closes.
Total: 1.9 MB across 124 files.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
88 lines
4.0 KiB
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88 lines
4.0 KiB
Plaintext
iter8 Zink-on-PanVk-Bifrost RED finding — captured 2026-05-19 on ohm
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(PineTab2 v2.0, RK3566, Mali-G52 r1 MC1, Mesa 26.0.6, kernel 7.0.0-danctnix1-6)
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===== eglinfo with Zink + PanVk attempted =====
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$ sudo -u mfritsche XDG_RUNTIME_DIR=/run/user/1001 WAYLAND_DISPLAY=wayland-0 \
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MESA_LOADER_DRIVER_OVERRIDE=zink PAN_I_WANT_A_BROKEN_VULKAN_DRIVER=1 eglinfo
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WARNING: panvk is not a conformant Vulkan implementation, testing use only.
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MESA: error: Zink requires the nullDescriptor feature of KHR/EXT robustness2.
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WARNING: panvk is not a conformant Vulkan implementation, testing use only.
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MESA: error: Zink requires the nullDescriptor feature of KHR/EXT robustness2.
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...
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OpenGL core profile vendor: Mesa
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OpenGL core profile renderer: llvmpipe (LLVM 22.1.3, 128 bits) ← FALLBACK
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OpenGL core profile version: 4.5 (Core Profile) Mesa 26.0.6-arch1.1
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RC=0 (but Zink did NOT load — fell back to llvmpipe SW rasterizer)
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===== PanVk-Bifrost vulkaninfo confirms robustness2 NOT in extension list =====
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$ PAN_I_WANT_A_BROKEN_VULKAN_DRIVER=1 vulkaninfo | grep -iE "robust|nullDescriptor"
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VkPhysicalDevicePipelineRobustnessPropertiesEXT: present
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defaultRobustnessStorageBuffers = ROBUST_BUFFER_ACCESS
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defaultRobustnessUniformBuffers = ROBUST_BUFFER_ACCESS
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defaultRobustnessVertexInputs = ROBUST_BUFFER_ACCESS
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defaultRobustnessImages = ROBUST_IMAGE_ACCESS
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Device extensions present:
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VK_EXT_image_robustness (different extension)
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VK_EXT_pipeline_robustness (different extension)
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VkPhysicalDeviceImageRobustnessFeaturesEXT.robustImageAccess = true
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VkPhysicalDevicePipelineRobustnessFeaturesEXT.pipelineRobustness = true
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NOT present:
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VK_EXT_robustness2 ← what Zink wants
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VK_KHR_robustness2 ← what Zink wants
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VkPhysicalDeviceRobustness2FeaturesEXT.nullDescriptor
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===== Mesa source: the gate =====
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File: ~/src/mesa-ref/mesa/src/panfrost/vulkan/panvk_vX_physical_device.c
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line 94: .KHR_robustness2 = PAN_ARCH >= 10,
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line 194: .EXT_robustness2 = PAN_ARCH >= 10,
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line 590: .nullDescriptor = PAN_ARCH >= 10,
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Bifrost is PAN_ARCH 6 (G31/G52/G72) or 7 (G52 r1/G76). Both fall OUTSIDE
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the `>= 10` gate. Mali-G52 r1 on ohm reports as PAN_ARCH=7 (per iter1 driver
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log: arch=7 in the panvk_physical_device.c switch statement).
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Valhall (PAN_ARCH=9), Bifrost, and the experimental v14 fifthgen are all
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denied robustness2 with the same hardcoded gate.
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===== Zink's hard requirement =====
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File: ~/src/mesa-ref/mesa/src/gallium/drivers/zink/zink_screen.c:3488-3489
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if (!screen->info.rb2_feats.nullDescriptor) {
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mesa_loge("Zink requires the nullDescriptor feature of KHR/EXT robustness2.");
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...
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}
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No ZINK_DEBUG flag in zink_screen.c:97-127 disables this check. The feature
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is a hard prerequisite for Zink.
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===== NIR side: the feature already plumbs through =====
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File: ~/src/mesa-ref/mesa/src/panfrost/vulkan/panvk_vX_nir_lower_descriptors.c:1309
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.null_descriptor_support = dev->vk.enabled_features.nullDescriptor,
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File: ~/src/mesa-ref/mesa/src/panfrost/vulkan/panvk_vX_shader.c:1355
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.robust_descriptors = dev->vk.enabled_features.nullDescriptor,
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The NIR lowering code already reads `enabled_features.nullDescriptor` —
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i.e., the plumbing exists per-arch. The gate at line 590 is what blocks
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the feature from being *enableable* on Bifrost; the underlying lowering
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machinery is already there and would activate if the feature were exposed.
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That doesn't guarantee Bifrost's hardware can correctly handle a null
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descriptor read (the gate may exist *because* Bifrost can't), but iter4
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proved descriptor handling works for valid cases — and "null descriptor"
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mostly means "shader accesses an unbound binding cleanly without GPU fault."
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===== Bigger picture =====
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This is the campaign's first real finding. PanVk-Bifrost is functionally
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solid for everything iter1–7 tested, but Zink (and presumably many other
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Vulkan apps that opt into modern descriptor features) requires extensions
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that PanVk-Bifrost gates out.
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For the TuxRacer-via-Zink path, this MUST be fixed before iter9 makes sense.
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