RedBear-OS/local/docs/LINUX-BORROWING-RUST-IMPLEMENTATION-PLAN.md

Linux Borrowing and Rust Implementation Plan for Red Bear OS

Date: 2026-04-18 Status: Planning authority for Linux-derived borrowing boundaries and Rust rewrite guidance across low-level subsystem work. PCI/IRQ rollout authority lives in local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md. Scope: Hardware enablement, ACPI including suspend/resume, low-level startup/init, PCI, IRQ/MSI/MSI-X, PS/2 init, IOMMU, USB/xHCI/storage, bounded Wi-Fi transport reuse, and selective GPU/DRM orchestration reuse

Intent

Which Linux kernel source and Linux documentation already present in this repo should be used as donor material for Red Bear OS, what should be rewritten into Rust, what should remain reference-only, and where should that logic live in Red Bear's architecture?

This plan is intentionally Red Bear-native. It does not propose importing Linux subsystem architecture into Red Bear.

Current implementation status snapshot (2026-04-18)

The software-only, bounded slices from this plan that are now implemented in code are:

• Phase A — PCI / IRQ substrate
  • bounded shared substrate slices landed in code (redox-driver-sys capability-chain parsing, interrupt-support summary, and early pcid convergence)
  • the canonical execution order, current robustness judgment, and remaining implementation work for PCI/IRQ now live in local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md
• Phase B — ACPI / IOMMU groundwork
  • acpid now carries an explicit userspace sleep-target model naming S1 / S3 / S4 / S5
  • only _S5 soft-off is materially wired today; non-S5 targets remain groundwork-only
  • iommu now detects kernel ACPI DMAR presence as a convergence seam, but Intel VT-d runtime ownership is not yet cleanly closed outside acpid
• Phase C — PS/2 / USB / storage
  • ps2d now flushes stale controller output during probe and around core init/self-test
  • xhcid now tracks active alternate settings and resolves endpoint descriptors through that map
  • usbscsid now has a bounded SYNCHRONIZE CACHE(10/16) heuristic behind needs_sync_cache
• Phase D — Wi-Fi / DRM shared-core
  • redbear-wifictl transport probing now uses the shared PCI parser and interrupt-support summary
  • redox-drm now exposes queued shared hotplug/vblank events through a real scheme EVENT_READ surface

The work that still remains is the larger vendor/backend maturation and hardware-validation side:

• full ACPI sleep/resume implementation beyond groundwork
• full Intel VT-d runtime support beyond DMAR ownership discovery
• deeper PCI / pcid convergence on shared helpers
• broader PS/2 resume/wake policy
• broader USB architecture/runtime maturation beyond the bounded helper slices already implemented
• deeper Wi-Fi transport/helper extraction beyond probing
• Intel and AMD DRM backend maturation and real hardware validation

This document should therefore be read as:

• implemented now for the bounded shared-core and software-only slices listed above
• still in progress for backend maturation and hardware-backed acceptance phases

Hard rules

1. Linux suspend/resume is reference-only. Red Bear should study Linux ordering and edge cases, but implement its own suspend/resume support in the Red Bear architecture.
2. linux-kpi is GPU and Wi-Fi only. It is not a general solution for ACPI, USB, input, startup, or general platform ownership.
3. Do not copy Linux subsystem structure blindly. Use Linux as an algorithm, quirk, parser, and sequencing donor; implement the resulting behavior in Red Bear’s own kernel/scheme/userspace-daemon model.
4. Keep Red Bear ownership boundaries intact. Kernel remains minimal; runtime/controller policy stays in userspace daemons; reusable low-level helpers converge into shared Rust crates.
5. Respect provenance and license constraints. Treat Linux driver code as reference/reverse-engineering input unless a bounded donor island already exists in-tree. Prefer datasheets when available.

Repo-grounded evidence base

Actual Linux-derived material in this repo

• Imported AMDGPU/DC tree: local/recipes/gpu/amdgpu-source/
• Bounded Intel Wi-Fi transport donor: local/recipes/drivers/redbear-iwlwifi/source/src/linux_port.c
• Linux compatibility layer for bounded donor ports: local/recipes/drivers/linux-kpi/
• Red Bear-native low-level substrate: local/recipes/drivers/redox-driver-sys/
• Linux-mined quirk system and tables:
  • local/recipes/drivers/redox-driver-sys/source/src/quirks/*
  • local/docs/QUIRKS-SYSTEM.md
• Linux source cache used as donor/reference material:
  • build/linux-kernel-cache/linux-7.0/

Linux source files directly relevant to this plan

• ACPI sleep and PM ordering:
  • build/linux-kernel-cache/linux-7.0/drivers/acpi/sleep.c
• PS/2 / i8042:
  • build/linux-kernel-cache/linux-7.0/drivers/input/serio/i8042.c
• PCI / quirks / MSI:
  • build/linux-kernel-cache/linux-7.0/drivers/pci/probe.c
  • build/linux-kernel-cache/linux-7.0/drivers/pci/quirks.c
  • build/linux-kernel-cache/linux-7.0/drivers/pci/msi/msi.c
• USB / xHCI / hub:
  • build/linux-kernel-cache/linux-7.0/drivers/usb/host/xhci-pci.c
  • build/linux-kernel-cache/linux-7.0/drivers/usb/core/hub.c
• Storage heuristics:
  • build/linux-kernel-cache/linux-7.0/drivers/scsi/sd.c
• IOMMU:
  • build/linux-kernel-cache/linux-7.0/drivers/iommu/amd/init.c
  • build/linux-kernel-cache/linux-7.0/drivers/iommu/intel/iommu.c
• GPU / DRM:
  • build/linux-kernel-cache/linux-7.0/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
  • build/linux-kernel-cache/linux-7.0/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
• Intel Wi-Fi transport:
  • build/linux-kernel-cache/linux-7.0/drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c

Linux documentation directly relevant to this plan

• Power / suspend:
  • build/linux-kernel-cache/linux-7.0/Documentation/power/suspend-and-interrupts.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/power/s2ram.rst
• PCI / interrupts:
  • build/linux-kernel-cache/linux-7.0/Documentation/PCI/msi-howto.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/PCI/boot-interrupts.rst
• Input / PS/2 context:
  • build/linux-kernel-cache/linux-7.0/Documentation/input/input-programming.rst
• ACPI:
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/acpi/acpi-drivers.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/acpi/scan_handlers.rst
• USB:
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/usb/writing_usb_driver.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/usb/mass-storage.rst
• GPU / DRM:
  • build/linux-kernel-cache/linux-7.0/Documentation/gpu/drm-kms.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/gpu/drm-uapi.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/gpu/drm-internals.rst
• Wi-Fi:
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/80211/introduction.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/80211/cfg80211.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/80211/mac80211.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/driver-api/80211/mac80211-advanced.rst
  • build/linux-kernel-cache/linux-7.0/Documentation/networking/napi.rst

Red Bear current-state and planning sources used

• docs/04-LINUX-DRIVER-COMPAT.md
• local/docs/ACPI-IMPROVEMENT-PLAN.md
• local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md
• local/docs/USB-IMPLEMENTATION-PLAN.md
• local/docs/USB-VALIDATION-RUNBOOK.md
• local/docs/WIFI-IMPLEMENTATION-PLAN.md
• local/docs/WIFI-VALIDATION-RUNBOOK.md
• local/docs/QUIRKS-SYSTEM.md
• local/docs/IOMMU-SPEC-REFERENCE.md
• local/docs/DBUS-INTEGRATION-PLAN.md
• local/docs/DRM-MODERNIZATION-EXECUTION-PLAN.md
• local/docs/CONSOLE-TO-KDE-DESKTOP-PLAN.md

---

Part 1 — Comprehensive assessment

1. Red Bear ownership model that must be preserved

Kernel-owned minimum platform baseline

Grounded in:

• recipes/core/kernel/source/src/startup/mod.rs
• recipes/core/kernel/source/src/startup/memory.rs
• recipes/core/kernel/source/src/acpi/mod.rs
• recipes/core/kernel/source/src/scheme/serio.rs

Kernel should keep only:

• boot memory/bootstrap
• early ACPI table discovery
• MADT / HPET / APIC / IRQ baseline
• race-critical serio byte queueing

Userspace runtime/controller ownership

Grounded in:

• recipes/core/base/source/drivers/hwd/src/main.rs
• recipes/core/base/source/drivers/hwd/src/backend/acpi.rs
• recipes/core/base/source/drivers/acpid/src/acpi.rs
• recipes/core/base/source/drivers/pcid/src/main.rs
• recipes/core/base/source/drivers/input/ps2d/src/controller.rs
• local/recipes/system/iommu/source/src/main.rs
• recipes/core/base/source/drivers/usb/xhcid/src/main.rs

Userspace owns:

• ACPI runtime and AML policy (acpid)
• PCI enumeration and driver-facing interrupt policy (pcid)
• IOMMU runtime ownership (iommu)
• PS/2 controller state machine (ps2d)
• USB controller/runtime policy (xhcid, related daemons)
• session-facing power signals (redbear-sessiond)
• Wi-Fi control/runtime policy (redbear-wifictl, redbear-netctl)

Shared Rust substrate

Grounded in:

• local/recipes/drivers/redox-driver-sys/source/src/{pci,irq,dma}.rs
• local/recipes/drivers/redox-driver-sys/source/src/quirks/*

Shared Rust should own:

• reusable PCI helpers
• MSI/MSI-X helpers
• DMA helpers
• quirk lookups
• future IVRS/DMAR helper modules

2. Actual startup / init ordering

Strict chain

Grounded in:

• recipes/core/base/source/drivers/hwd/src/backend/acpi.rs
• recipes/core/base/source/drivers/hwd/src/main.rs
• recipes/core/base/source/drivers/acpid/src/acpi.rs

Strict order:

1. kernel bootstrap / memory / early ACPI / IRQ / serio baseline
2. userspace bootstrap
3. hwd starts
4. hwd ACPI backend spawns acpid
5. hwd main spawns pcid
6. acpid waits for PCI registration before AML-symbol readiness

Shared initfs target membership (not strict serialization)

Grounded in:

• recipes/core/base/source/init.initfs.d/40_hwd.service
• recipes/core/base/source/init.initfs.d/40_pcid-spawner-initfs.service
• recipes/core/base/source/init.initfs.d/40_ps2d.service
• recipes/core/base/source/init.initfs.d/40_drivers.target
• recipes/core/base/source/init.initfs.d/10_inputd.service
• recipes/core/base/source/init.initfs.d/10_lived.service
• recipes/core/base/source/init.initfs.d/20_graphics.target

Important nuance:

• ps2d, hwd, and pcid-spawner-initfs all participate in early initfs driver bring-up.
• They are grouped by 40_drivers.target, but they are not one single strict serial chain.

3. What Linux material Red Bear should borrow into Rust

Subsystem matrix

Subsystem	Linux donor material	Rewrite into Rust	Keep reference-only	Red Bear owner
ACPI / suspend	drivers/acpi/sleep.c, Documentation/power/*, Documentation/driver-api/acpi/*	sleep sequencing helpers, AML/power orchestration helpers, wake-source modeling	Linux PM core, ACPI device-node driver ownership	acpid, redbear-sessiond
PCI	drivers/pci/probe.c, drivers/pci/quirks.c, Documentation/PCI/*	capability walkers, BAR/resource validation, fixup/quirk pass model	Linux PCI core ownership	pcid, redox-driver-sys
IRQ / MSI / MSI-X	drivers/pci/msi/*, PCI docs	interrupt mode selection, vector policy, masking/fallback helpers	Linux generic IRQ core	kernel irq:, pcid, redox-driver-sys
PS/2 / i8042	drivers/input/serio/i8042.c, input docs	reset/resume policy, aux/mux quirks, recovery deltas only	Linux input core	serio, ps2d
IOMMU	drivers/iommu/amd/init.c, drivers/iommu/intel/iommu.c	IVRS/DMAR parsers, table encoders, pre-enabled translation handling	Linux iommu-core structure	iommu, shared Rust helpers
USB / xHCI	drivers/usb/host/xhci-pci.c, drivers/usb/core/hub.c, USB docs	quirk logic, suspend/resume sequencing, composite/interface correctness	Linux USB core / driver model	xhcid, usbhubd, usbscsid
USB storage	drivers/scsi/sd.c, Documentation/usb/mass-storage.rst	bounded cache/flush/capacity heuristics	broad Linux SCSI midlayer architecture	usbscsid
Wi-Fi	iwlwifi transport, 80211 docs, NAPI docs	selected queue/DMA/IRQ/timeout helper patterns only	cfg80211/mac80211/NAPI architecture	bounded donor transport + native wifictl/netctl
GPU / DRM	amdgpu_device.c, amdgpu_dm.c, DRM docs, imported AMDGPU tree	orchestration, phase sequencing, quirk policy, selected shared helpers later	full DRM/AMDGPU runtime architecture	redox-drm, bounded vendor backends

4. What Linux material must remain reference-only

• Linux PM core
• Linux driver core
• Linux USB core
• Linux input core
• Linux wireless subsystem architecture (cfg80211, mac80211, NAPI ownership model)
• Linux tasklet/workqueue ownership model
• Full AMDGPU runtime architecture

Reason: all of those conflict with the ownership rules that Red Bear already implements and should keep.

5. What Red Bear still materially needs

• ACPI sleep beyond _S5
• clean Intel VT-d / DMAR runtime ownership outside acpid
• better PCI host bridge / interrupt-link handling
• quirk convergence in redox-driver-sys
• USB composite/interface correctness
• hardware validation before deeper GPU/Wi-Fi extraction

---

Part 2 — How to implement it in Red Bear OS

1. Placement rules

Kernel

Keep only:

• bootstrap
• memory initialization
• early ACPI table discovery
• APIC/HPET/IRQ baseline
• race-critical serio

Userspace daemons

• acpid: ACPI runtime policy, AML, sleep orchestration
• pcid: PCI enumeration/config/capability export/interrupt mode policy
• iommu: AMD-Vi / VT-d runtime ownership
• ps2d: PS/2 controller init/reset/resume/data path
• xhcid, usbhubd, usbscsid: controller/hub/storage runtime logic
• redbear-sessiond: D-Bus/session-facing sleep/shutdown bridge
• redbear-wifictl, redbear-netctl: native Wi-Fi control plane

Shared Rust crates

• redox-driver-sys: canonical home for reusable PCI/IRQ/DMA/quirk/IOMMU helpers
• linux-kpi: bounded donor bridge for GPU/Wi-Fi only

2. Implementation order

For current execution order, priority ranking, and acceptance language:

• use local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md for PCI / IRQ / low-level controller work,
• use local/docs/ACPI-IMPROVEMENT-PLAN.md for ACPI ownership/robustness/sleep work,
• use local/docs/USB-IMPLEMENTATION-PLAN.md for USB maturity,
• and use the Wi-Fi / DRM plans for those later subsystem-specific phases.

This file should keep the borrowing and rewrite policy for those phases, not act as a competing execution roadmap.

3. Work package backlog

Phase A — PCI / IRQ / quirk substrate

For Phase A execution detail, file targets, acceptance criteria, and validation language, use the canonical PCI/IRQ plan:

• local/docs/IRQ-AND-LOWLEVEL-CONTROLLERS-ENHANCEMENT-PLAN.md

This document keeps only the borrowing-policy summary for Phase A:

• borrow Linux capability/fixup/MSI semantics as donor knowledge,
• reimplement them as typed Rust helpers in redox-driver-sys / pcid,
• prefer data-driven quirks over daemon-local special cases,
• and do not import Linux generic IRQ-core ownership into Red Bear.

Current implementation progress remains true but is intentionally summarized only:

• shared PCI capability parsing and interrupt-support summarization are already present in redox-driver-sys,
• and the remaining rollout/convergence work now belongs to the canonical IRQ plan rather than this borrowing-policy document.

Phase B — ACPI / suspend / IOMMU

Primary targets

• recipes/core/base/source/drivers/acpid/src/acpi.rs
• recipes/core/base/source/drivers/acpid/src/sleep.rs (new)
• local/recipes/system/iommu/source/src/main.rs
• shared future IVRS/DMAR helper modules in redox-driver-sys

Implement

• Red Bear-native sleep coordinator
• _PTS / _WAK / wake-source handling helpers
• IVRS/DMAR parsers and table builders
• move long-term DMAR runtime ownership into iommu

Acceptance

• _S5 preserved
• explicit sleep phase machine exists
• IOMMU ownership clarified and moved out of acpid

Current implementation progress (2026-04-18)

• acpid now has an explicit SleepTarget / SleepPhase model in userspace, naming S1, S3, S4, and S5 as Red Bear sleep targets.
• The real shutdown path now routes through that target model, while non-S5 targets are recognized but still remain groundwork-only rather than implemented suspend/resume support.
• Unit coverage exists for sleep-target parsing, AML sleep-object naming, and the current Red Bear-native rule that only S5 is treated as an implemented soft-off path today.
• This is still groundwork only: there is no claim of full suspend/resume or sleep eventing yet, and Linux suspend sequencing remains reference material rather than imported structure.
• The iommu daemon now also detects the presence of a kernel ACPI DMAR table and reports that Intel VT-d runtime ownership should converge there instead of remaining conceptually attached to the old transitional acpid DMAR code, but that ownership is not yet cleanly closed in the current tree.

Phase C — PS/2 / USB / storage

Primary targets

• recipes/core/base/source/drivers/input/ps2d/src/{controller,state}.rs
• recipes/core/base/source/drivers/usb/xhcid/src/xhci/*
• recipes/core/base/source/drivers/storage/usbscsid/src/*

Implement

• PS/2 reset/resume hardening
• xHCI quirk and interface-selection corrections
• bounded storage heuristics from Linux SCSI logic

Acceptance

• PS/2 proof remains green
• xHCI and USB maturity proofs remain green
• no Linux USB/input-core structure imported

Current implementation progress (2026-04-18)

• xhcid now tracks active alternate settings per interface and resolves endpoint descriptors using that active-alternate map instead of flattening all interface descriptors in a configuration.
• Direct unit coverage exists for default-alternate endpoint selection and alternate-setting-aware endpoint remapping, closing the most explicit in-tree USB interface-selection TODO without importing Linux USB-core structure.
• xhcid now also preserves previously selected alternates on the same configuration and applies a requested interface/alternate override before endpoint planning, so alternate-setting reconfiguration no longer silently falls back to all-zero defaults.
• xhcid endpoint-direction lookup now also follows the active interface/alternate selection state instead of reading from the first configuration/interface pair unconditionally.
• xhcid driver spawning now also follows the selected configuration and active alternate map instead of hardcoding the first configuration and ignoring non-zero alternates.
• xhcid now also has a preserve-and-grow event-ring path in the IRQ reactor, so EventRingFull recovery no longer drops unread event TRBs while resizing the primary event ring.
• usbhubd and xhcid now propagate USB 2 hub TT Think Time from the parent hub descriptor into the xHCI Slot Context TT information bits using a bounded Linux-compatible encoding path.
• xhcid endpoint-context calculations are now protocol-speed-aware for SuperSpeedPlus, so interval and ESIT-payload selection distinguish SSP paths from generic SuperSpeed using the resolved port protocol speed rather than only endpoint companion presence.
• usbscsid now has a bounded native SYNCHRONIZE CACHE(10/16) heuristic gated by the existing needs_sync_cache storage quirk, directly reflecting the planned Linux sd.c donor usage without importing Linux SCSI midlayer structure.
• ps2d now performs an explicit controller-output flush during probe and at the key controller reinitialization boundaries in Ps2::init(), matching the Linux i8042_flush() discipline in a bounded Red Bear-native way without importing Linux input-core structure.

Phase D — Wi-Fi and GPU/DRM

Primary targets

• local/recipes/system/redbear-wifictl/source/*
• local/recipes/system/redbear-netctl/source/*
• local/recipes/gpu/redox-drm/source/*

Implement

• only reusable queue/DMA/IRQ helper extraction from bounded Wi-Fi donor transport
• only orchestration / phase sequencing / quirk policy extraction for DRM

Acceptance

• control plane remains native
• DRM display-vs-render boundary remains explicit
• no claim of full AMDGPU rewrite or Linux wireless-architecture import

Current implementation progress (2026-04-18)

• redbear-wifictl transport probing now uses the shared redox-driver-sys PCI parser and the shared quirk-aware interrupt-support summary instead of relying only on local raw-config logic.
• This is a bounded helper extraction only: the native Wi-Fi control plane remains authoritative, and there is still no import of Linux wireless subsystem structure.
• redox-drm now turns shared hotplug and vblank events into a queued scheme-visible EVENT_READ surface for card0, with hotplug also reaching the matching connector handle. That makes shared DRM event delivery observable without conflating it with render-fence semantics.

4. Subsystem-specific code guidelines

ACPI / suspend

• Use Linux power docs/source for sequencing and debugging principles only.
• Do not port Linux PM callback ownership.
• Keep ACPI policy in acpid and session-facing signaling in redbear-sessiond.

PCI / IRQ

• Reimplement Linux capability/fixup logic as typed Rust helpers.
• Prefer data-driven quirks over daemon-local special cases.

PS/2

• Treat current serio + ps2d as correct baseline.
• Only import missing deltas from Linux i8042.c.

IOMMU

• Reimplement parsing/table logic in Rust.
• Keep runtime MMIO ownership in userspace iommu.

USB

• Borrow Linux quirks and sequencing; keep controller ownership in Rust daemons.
• Do not recreate Linux USB driver registration models.

Wi-Fi

• Keep Linux 80211 docs as reference-only behavior material.
• Keep cfg80211 / mac80211 / NAPI architecture out of Red Bear.

GPU / DRM

• Use Linux DRM docs and donor code to inform orchestration and boundary discipline.
• Do not treat imported AMDGPU code as a roadmap for wholesale Rust replacement.

5. Validation and evidence rules

Every Linux-derived rewrite should clear these gates in order:

1. Donor identified — exact Linux source/doc named
2. Rust landing point identified — exact crate/module/file named
3. Boundary stated — rewrite target vs reference-only
4. Build-valid — compiles cleanly
5. Runtime-valid — bounded proof exists
6. Hardware-valid — only once target hardware evidence exists

Do not collapse those categories. Build success is not runtime proof, and runtime proof is not hardware support.

6. Final policy summary

The correct Red Bear approach is:

• borrow Linux knowledge, algorithms, parsers, quirk semantics, and phase sequencing
• rewrite those into Rust helpers and Red Bear-native state machines
• keep the kernel minimal
• keep runtime/controller policy in userspace daemons
• keep linux-kpi bounded to GPU/Wi‑Fi donor islands only
• avoid importing Linux subsystem ownership models into Red Bear OS