Record: Fan control service implementation — 2026-08-23

Outcome

Implemented the C++ fan-control service on the skeleton base.

Modules:

• sources/gpu_interface.{h,cpp}: MI25 discovery by PCI identity, sysfs reads and writes with errno propagation.
• sources/fan_curve.{h,cpp}: stage tables, interpolation, and PWM ramp.
• sources/mi25_fan_control.cpp: startup sequence, control loop, reporting, and failure policy.
• CMakeLists.txt, .clang-format: build and format.
• scripts/install.sh, scripts/amd-mi25-fanctl.service: install and unit.
• tests/02-fan-control.sh: fixture-based test (tool-gated).

Verified behavior against a sysfs fixture:

• Discovery picks the MI25 card (vendor 0x1002, device 0x6860) and rejects other cards.
• –check verifies the interface and fails when pwm1_enable is missing.
• The control loop computes the interpolated target (67 at 47 C) and ramps the fan up by 10 per second.
• Fingerprinting reports kernel release and driver version.

Decisions

• Unit name amd-mi25-fanctl.service.
• Startup writes pwm1_enable=1, manual, COMPUTE profile, minimum PWM.
• Failure policy follows documents/07-failure-behavior.md.
• make build compiles the C++ service; make test runs the fixture test.

Verification

• make build succeeds with -Werror.
• make test passes (00-skeleton, 01-site-build, 02-fan-control).
• ctest passes (smoke_test, fan_control_interface_test).
• clang-format clean.

Commits

• (recorded in git history for this task)