RFC: First Userspace Intel NPU Driver for Redox OS (Meteor Lake VPU 4.0)

[JoseRFJuniorLLMs]

Summary

I've built what I believe is the world's first userspace NPU (Neural Processing Unit) driver for a microkernel operating system. It targets the Intel Meteor Lake NPU (VPU 4.0, PCI ID 0x7D1D) and runs entirely in Redox OS userspace — zero kernel modifications required.

This is an interest check before submitting a merge request to the Redox ecosystem (redox-os/drivers or redox-os/cookbook).

Why This Matters for Redox

1. Validates the microkernel driver model — A real hardware driver (not a toy) running entirely via Redox schemes, proving that complex DMA-based drivers work in userspace.

2. First NPU support for any microkernel OS — No microkernel (Minix, seL4, Fuchsia, Redox) currently has an NPU driver. This opens AI/ML inference capabilities.

3. Fills an unaddressed gap — The Redox Development Priorities for 2025/26 mention GPU, WiFi, USB, and I2C, but not NPU. As AI workloads become standard, NPU support will be expected.

Architecture

+----------------------------------------------------------+
|                    Userspace (our driver)                 |
|                                                          |
|  +----------+  +----------+  +-----------+  +--------+  |
|  |   PCI    |  |   MMIO   |  |    DMA    |  |  Boot  |  |
|  | Discovery|  |  BAR0    |  | phys_cont.|  |Sequence|  |
|  +----+-----+  +----+-----+  +-----+-----+  +---+----+  |
|       |              |              |             |       |
|  +----+--------------+--------------+-------------+---+  |
|  |              npu: Scheme Handler                    |  |
|  |   open("npu:infer") -> write(model) -> read(result)|  |
|  +---------------------------------------------------------+
+---------------------------+------------------------------+
                            | Redox Schemes
+---------------------------+------------------------------+
|                    Redox Kernel                           |
|              (ZERO modifications needed)                  |
+----------------------------------------------------------+

Key Design Decisions

Decision	Approach	Rationale
DMA allocation	memory:phys_contiguous?size=N&uncacheable	Existing Redox scheme, no kernel changes
Register access	MMIO via BAR0 fmap + volatile reads/writes	Standard PCI BAR mapping
Firmware loading	Load to DMA buffer, write phys addr to NPU registers	Matches Linux ivpu driver flow
IPC protocol	Hexspeak handshake: 0xF00D=Ready, 0xDEAD=Fatal, 0xCAFE=Nudge	Reverse-engineered from Linux ivpu_hw_40xx.c
User interface	npu: scheme (open/read/write/close)	Native Redox "everything is a URL" philosophy
Command queue	Ring buffer (256 x 64-byte descriptors) in DMA memory	Standard hardware command submission pattern

Files

File	Lines	Purpose
main.rs	~240	Entry point, 6-phase startup orchestration
boot.rs	~380	Power-up, firmware load, doorbell handshake with nudge strategy
dma.rs	~390	DMA buffer via phys_contiguous, volatile I/O, firmware loader
pci.rs	~290	PCI bus scan, Bus Mastering, BAR0 mapping
mmio.rs	~170	Safe MMIO abstraction (volatile, fenced, bounds-checked)
hw_mtl.rs	~210	Register map (reverse-engineered from Linux ivpu driver)
inference.rs	~290	Command queue ring buffer, job submission
scheme.rs	~130	Redox npu: scheme (file-based inference API)
status.rs	~175	Health monitor, state machine, diagnostics

Total: ~2,275 lines of Rust, with full mock mode for development on Linux/macOS/Windows.

Safety & Audit Status

The driver has been through 10 recursive security audits covering:

• Memory safety & UB analysis
• Integer overflow protection
• Hardware protocol correctness
• Resource leak prevention
• Security & attack surface

22 critical/high findings were identified and fixed, including:

• Correct doorbell trigger value (0x80000000, bit 31)
• Clock-before-reset boot order (matching Linux ivpu driver)
• Volatile DMA reads/writes throughout
• Firmware magic byte validation
• UID authorization on npu:infer scheme access
• Overflow-safe MMIO bounds checks (no panics -- returns 0xFFFFFFFF like PCI)

Hardware Support

Device	PCI ID	Status
Meteor Lake NPU (VPU 4.0)	0x7D1D	Primary target
Arrow Lake NPU (VPU 4.0)	0xAD1D	Register map ready
Lunar Lake NPU (VPU 5.0)	0x6467	Future

What I'm Looking For

1. Feedback on whether this fits in redox-os/drivers or redox-os/cookbook
2. Code review from the Redox community on the scheme design and DMA approach
3. Guidance on the preferred directory structure and build integration
4. Testing help from anyone with Meteor Lake hardware running Redox

References

• Linux ivpu driver: drivers/accel/ivpu/
• Intel NPU firmware: linux-firmware.git -> intel/vpu/vpu_40xx_v*.bin
• Redox memory:phys_contiguous: used by existing Redox drivers for DMA
• Source code: drive/ in this repository

About

This driver was developed as part of the EVA OS project -- an AI-powered virtual assistant ecosystem. The NPU driver enables on-device neural inference for speech processing, image recognition, and real-time AI tasks without relying on cloud APIs.

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Feedback welcome here, on the Redox Matrix chat (#redox:matrix.org), or on the Redox GitLab (gitlab.redox-os.org).