RedBear-OS/local/docs/archived/XHCID-DEVICE-IMPROVEMENT-PLAN.md

xhcid Device-Level Improvement Plan

Purpose

This document defines the implementation sequence for hardening xhcid at the device level in Red Bear OS.

It is a focused companion to local/docs/USB-IMPLEMENTATION-PLAN.md. The USB plan remains the subsystem-wide authority; this document narrows scope to the xhcid device lifecycle, configuration, teardown, PM behavior, enumerator robustness, and bounded proof coverage.

Scope

In scope:

• recipes/core/base/source/drivers/usb/xhcid/src/xhci/device_enumerator.rs
• recipes/core/base/source/drivers/usb/xhcid/src/xhci/mod.rs
• recipes/core/base/source/drivers/usb/xhcid/src/xhci/scheme.rs
• recipes/core/base/source/drivers/usb/xhcid/src/xhci/irq_reactor.rs
• bounded QEMU validation scripts under local/scripts/
• canonical USB documentation under local/docs/

Out of scope:

• generic USB redesign
• unrelated class-driver feature work
• hardware-validation claims beyond what the repo can currently prove

Repo-Fit Note

Technical implementation targets live in upstream-owned source under recipes/core/base/source/..., but durable Red Bear preservation belongs in local/patches/base/. This plan names the technical work locations, not a recommendation to leave work stranded only in upstream-owned trees.

Current Audited Findings

The current xhcid tree has already improved materially:

• lifecycle gating exists through PortLifecycle and PortOperationGuard
• configure_endpoints_once() is now transactional relative to earlier behavior
• detach waits before removing published state
• a bounded QEMU lifecycle proof exists

Remaining risks:

• partial attach visibility still exists around publication timing
• detach can still depend on bounded-but-incomplete purge semantics
• suspend/resume is still mainly software gating
• rollback failure is not yet a fully hardened degraded-state path
• enumerator logic still relies on timing- and assumption-heavy behavior
• proof coverage is still QEMU-bounded and misses key interleavings

Design Invariants

The implementation should satisfy these invariants:

1. No half-attached device is publicly usable.
2. No new work is admitted after detach begins.
3. Detach always reaches a bounded terminal outcome.
4. Failed configure leaves either the old config intact or the device explicitly degraded/reset-required.
5. PM transitions reflect actual usable state, not only software policy.
6. Enumerator behavior is bounded and diagnosable, not panic-driven.
7. Validation claims match what scripts actually prove.

Phase 1 — Proof-First Expansion

Goal

Make the current blind spots reproducible before changing behavior.

Work

• extend test-xhci-device-lifecycle-qemu.sh
• extend test-usb-qemu.sh
• extend test-xhci-irq-qemu.sh
• add bounded injection hooks in xhcid for configure-failure and attach/detach timing cases

Required Cases

• repeated attach/detach
• detach during storage startup
• transfer-during-detach surrogate
• configure failure injection
• suspend/resume admission checks
• rapid event ordering cases

Per-File Focus

local/scripts/test-xhci-device-lifecycle-qemu.sh

• add repeated HID/storage attach-detach loops
• add detach-during-driver-start for storage
• add storage attach long enough to exercise startup/read activity before unplug
• require explicit attach-entered, attach-finished, detach-completed evidence

local/scripts/test-usb-qemu.sh

• separate boot progress from proof failure
• keep result lines distinct for xHCI init, HID spawn, SCSI spawn, bounded readback, and crash scan
• add repeated full-stack run mode or bounded loop count if needed for ordering-sensitive regressions

local/scripts/test-xhci-irq-qemu.sh

• verify interrupt-mode evidence still holds under actual attached-device pressure, not only empty-controller boot

xhci test hooks

• add bounded test-only failure hooks in scheme.rs / mod.rs for:
  • fail after CONFIGURE_ENDPOINT
  • fail after SET_CONFIGURATION
  • optional delay before final attach commit
• current bounded implementation uses one-shot guest-side commands written to /tmp/xhcid-test-hook, consumed by xhcid on the next matching lifecycle point

Exit Criteria

• scripts are syntax-clean
• new cases fail meaningfully on current gaps
• failures identify the specific missed milestone

Phase 2 — Atomic Attach Publication

Goal

Prevent half-built devices from becoming publicly reachable.

Work

• refactor Xhci::attach_device
• split attach staging from published PortState
• narrow lifecycle exposure so scheme paths cannot reach a device before final commit
• make attach cleanup direct for prepublication failure

Key Targets

• xhci/mod.rs::Xhci::attach_device
• xhci/mod.rs::PortLifecycle::*
• xhci/device_enumerator.rs::DeviceEnumerator::run

Per-File Focus

xhci/mod.rs

• stop inserting into port_states before all attach substeps complete
• keep slot, input context, EP0 ring, quirks, and descriptors in a private staging carrier
• commit published PortState in one final block
• keep prepublication cleanup separate from detach_device() where possible

xhci/device_enumerator.rs

• ensure duplicate connect handling still treats EAGAIN or equivalent as "already published" rather than "half-built staging state"

Exit Criteria

• no public state before attach commit
• attach failure leaves no published device and no child driver

Phase 3 — Bounded Detach and Purge

Goal

Make teardown bounded, dominant, and safe against stale completions.

Work

• bound PortLifecycle::begin_detaching()
• reject all new work immediately once detach starts
• purge or tombstone pending transfer/reactor state
• separate graceful drain from forced teardown
• preserve correct slot-disable/remove ordering
• ensure child-driver shutdown cannot wedge detach

Key Targets

• xhci/mod.rs
• xhci/irq_reactor.rs
• transfer bookkeeping in xhci/scheme.rs

Per-File Focus

xhci/mod.rs

• add timeout or bounded wait to detach drain logic
• distinguish graceful drain from forced teardown
• keep port_states.remove(...) after terminal teardown outcome

xhci/irq_reactor.rs

• add per-port invalidation or tombstone behavior so stale completions cannot target removed state

xhci/scheme.rs

• ensure operation-entry helpers fail immediately once detach starts

Exit Criteria

• detach cannot hang forever
• no stale completion can target removed device state
• unload-under-activity proof passes

Phase 4 — Configure Rollback Hardening

Goal

Make configuration changes fully transactional and recoverable.

Work

• formalize stage/program/commit boundaries
• ensure snapshots cover all mutated controller-facing state
• promote rollback failure into explicit degraded-state handling
• define deterministic behavior for post-SET_CONFIGURATION failure
• keep alternate/config bookkeeping coherent after rollback
• quarantine or reset on unrecoverable ambiguity

Key Targets

• xhci/scheme.rs::configure_endpoints_once
• restore_configure_input_context
• configure_endpoints
• set_configuration
• set_interface

Per-File Focus

xhci/scheme.rs

• keep endpoint/ring state staged until commit
• verify snapshots cover every mutated slot/endpoint field
• treat rollback failure as a first-class degraded state
• ensure post-failure descriptor and alternate bookkeeping still reflect live state

Exit Criteria

• injected configure failure preserves old state or explicitly degrades/resets device
• no staged endpoint state leaks into live software state

Phase 5 — Real PM Sequencing

Goal

Replace software-only PM gating with meaningful quiesce/resume semantics.

Work

• define richer PM transition states
• quiesce before suspend
• tie resume to controller/device validity
• define PM interaction with detach
• define PM interaction with configure
• add bounded PM proof cases

Key Targets

• xhci/scheme.rs::suspend_device
• xhci/scheme.rs::resume_device
• xhci/scheme.rs::ensure_port_active
• supporting helpers in xhci/mod.rs

Exit Criteria

• suspend blocks new I/O only after quiesce starts
• resume only returns success from a genuinely usable state
• PM/detach/configure interleavings are deterministic

Phase 6 — Enumerator Cleanup and Timing Hardening

Goal

Remove panic-style and magic-delay behavior from the enumerator path.

Work

• remove panic-class assumptions from DeviceEnumerator::run
• replace fixed sleeps with bounded readiness checks
• make duplicate/out-of-order event handling explicit
• align enumerator decisions with the new attach/detach state machine
• improve logging for reset/attach/detach milestones

Key Targets

• xhci/device_enumerator.rs
• supporting interactions in xhci/mod.rs

Exit Criteria

• no ordinary event path panics
• no unnecessary fixed sleep remains
• rapid event-order tests pass in QEMU

Phase 7 — Final Validation, Docs, and Preservation

Goal

Close the loop with evidence, canonical docs, and durable patch carriers.

Work

• rerun the full bounded proof matrix on a rebuilt image
• run source-level verification (lsp_diagnostics, cargo check, cargo test)
• update canonical docs:
  • local/docs/USB-IMPLEMENTATION-PLAN.md
  • local/docs/USB-VALIDATION-RUNBOOK.md
• immutable archived durable patch carriers under local/patches/base/
• delete only clearly stale, superseded docs after link sweep

Exit Criteria

• all bounded USB/xHCI proofs pass on a fresh image
• changed files are diagnostics-clean
• canonical docs match actual proof scope
• patch carrier is immutable archived and reapplicable

Validation Matrix

Required final proofs:

• bash ./local/scripts/test-xhci-device-lifecycle-qemu.sh --check <tracked-target>
• bash ./local/scripts/test-usb-qemu.sh --check <tracked-target>
• bash ./local/scripts/test-xhci-irq-qemu.sh --check
• bash ./local/scripts/test-usb-maturity-qemu.sh <tracked-target>

Required source checks:

• lsp_diagnostics on all changed files
• cargo check / cargo test for xhcid
• cargo check for any touched class daemon or helper crate

Commit Strategy

1. proof/harness expansion
2. atomic attach publication
3. bounded detach and purge
4. configure rollback hardening
5. PM sequencing
6. enumerator cleanup
7. docs, patch preservation, stale-doc cleanup

Canonical Doc Authority

Authoritative docs after cleanup:

• local/docs/USB-IMPLEMENTATION-PLAN.md
• local/docs/USB-VALIDATION-RUNBOOK.md

This xhcid plan is a focused implementation document beneath those subsystem-level authorities.

Completion Standard

This work is complete only when:

• all seven phases are done in order
• no changed-file diagnostics remain
• xhcid builds/tests cleanly
• bounded QEMU proof matrix passes on a rebuilt image
• canonical docs are synchronized
• durable patch carrier is immutable archived
• remaining gaps, if any, are explicitly documented as future or hardware-only work