Rust power_supply abstraction + SMB347 charger driver

A Rust abstraction for the Linux power supply class — which does not currently exist in mainline or rust-next — together with the SMBus helpers needed to drive an I²C charger from Rust, and a Rust port of the Summit SMB347 battery charger as the first consumer.

Status: RFC, based on rust-next (v7.2-rc1). Submitted upstream 2026-07-08 — lore thread.

Motivation

Rust drivers for power-supply hardware are currently blocked: there is no safe Rust interface to the power supply class, and the I2cClient abstraction exposes no register I/O. This series provides a minimal, self-contained path from binding an I²C charger to reporting charging state through sysfs, entirely in safe Rust, with the unsafe FFI confined to the two abstraction layers.

The series (abstraction-first)

Full diffstat: 8 files changed, 373 insertions(+).

Layout

rust/kernel/power_supply.rs                 # the abstraction (patch 2, browsable)
drivers/power/supply/smb347-charger_rust.rs # the driver       (patch 3, browsable)
patches/                                    # the full RFC series + cover letter
  0000-cover-letter.patch
  0001-rust-i2c-add-SMBus-byte-transfer-helpers.patch
  0002-rust-power_supply-add-power-supply-class-abstraction.patch
  0003-power-supply-add-Rust-SMB347-charger-driver.patch

The two .rs files above are the new files from the series, included here for easy reading. To apply the complete change set (including the edits to rust/kernel/i2c.rs, rust/kernel/lib.rs, rust/bindings/bindings_helper.h, MAINTAINERS, and the Kconfig / Makefile entries), use the patches:

cd linux            # a rust-next / v7.2-rc1 tree
git am /path/to/patches/000{1,2,3}-*.patch

Testing

Built and exercised against an emulated SMB347 using i2c-stub: seeding the chip's status registers and reading back the corresponding sysfs attributes (status, online, charge_type) confirms the full C→Rust→C path. No physical hardware or interrupt path has been tested.

Known limitations (hence RFC)

• get_property recovers the driver's private data via the parent device's drvdata, relying on the observed ordering that callbacks only fire after probe() has set it; the contract should be made explicit.
• smbus_update_bits() is not atomic against concurrent callers; a lock will be required before a charger IRQ handler is added (not yet implemented).
• Only get_property and a handful of properties are wired up; set_property, property_is_writeable, and IRQ-driven power_supply_changed() notification are future work.

License

GPL-2.0, matching the Linux kernel. The source files carry SPDX-License-Identifier headers.

---

Author: Bruce Robertson brucer42@gmail.com.