Message-Id: <20250617-rust-next-pwm-working-fan-for-sending-v3-0-1cca847c6f9f@samsung.com>
Date: Tue, 17 Jun 2025 16:07:23 +0200
From: Michal Wilczynski <m.wilczynski@...sung.com>
To: Uwe Kleine-König <ukleinek@...nel.org>,  Miguel Ojeda
	<ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,  Boqun Feng
	<boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,  Andreas
	Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,  Trevor
	Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,  Michal
	Wilczynski <m.wilczynski@...sung.com>, Drew Fustini <drew@...7.com>,  Guo
	Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>,  Rob Herring
	<robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,  Conor Dooley
	<conor+dt@...nel.org>,  Paul Walmsley <paul.walmsley@...ive.com>,  Palmer
	Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,  Alexandre
	Ghiti <alex@...ti.fr>,  Marek Szyprowski <m.szyprowski@...sung.com>,  Benno
	Lossin <lossin@...nel.org>,  Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Benno Lossin <lossin@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-clk@...r.kernel.org,  Krzysztof Kozlowski
	<krzysztof.kozlowski@...aro.org>
Subject: [PATCH v3 0/9] Rust Abstractions for PWM subsystem with TH1520 PWM
 driver

This patch series introduces Rust support for the T-HEAD TH1520 PWM
controller and demonstrates its use for fan control on the Sipeed Lichee
Pi 4A board.

The primary goal of this patch series is to introduce a basic set of
Rust abstractions for the Linux PWM subsystem. As a first user and
practical demonstration of these abstractions, the series also provides
a functional PWM driver for the T-HEAD TH1520 SoC. This allows control
of its PWM channels and ultimately enables temperature controlled fan
support for the Lichee Pi 4A board. This work aims to explore the use of
Rust for PWM drivers and lay a foundation for potential future
Rust based PWM drivers.

The core of this series is a new rust/kernel/pwm.rs module that provides
abstractions for writing PWM chip provider drivers in Rust. This has
been significantly reworked from v1 based on extensive feedback. The key
features of the new abstraction layer include:

 - Ownership and Lifetime Management: The pwm::Chip wrapper is managed
   by ARef, correctly tying its lifetime to its embedded struct device
   reference counter. Chip registration is handled by a pwm::Registration
   RAII guard, which guarantees that pwmchip_add is always paired with
   pwmchip_remove, preventing resource leaks.

 - Modern and Safe API: The PwmOps trait is now based on the modern
   waveform API (round_waveform_tohw, write_waveform, etc.) as recommended
   by the subsystem maintainer. It is generic over a driver's
   hardware specific data structure, moving all unsafe serialization logic
   into the abstraction layer and allowing drivers to be written in 100%
   safe Rust.

 - Ergonomics: The API provides safe, idiomatic wrappers for other PWM
   types (State, Args, Device, etc.) and uses standard kernel error
   handling patterns.

The series is structured as follows:
 - Rust PWM Abstractions: The new safe abstraction layer.
 - TH1520 PWM Driver: A new Rust driver for the TH1520 SoC, built on
   top of the new abstractions.
 - Clock Fix: A necessary fix to the TH1520 clock driver to ensure bus
   clocks remain enabled.
 - Device Tree Bindings & Nodes: The remaining patches add the necessary
   DT bindings and nodes for the TH1520 PWM controller, a thermal
   sensor, and the PWM fan configuration for the Lichee Pi 4A board.

Testing:
Tested on the TH1520 SoC. The fan works correctly. The duty/period
calculaties are correct. Fan starts slow when the chip is not hot and
gradually increases the speed when PVT reports higher temperatures.

The patches are based on mainline, with some dependencies which are not
merged yet - platform Io support [1] and math wrapper [2].

Reference repository with all the patches together can be found on
github [3].

[1] - https://lore.kernel.org/rust-for-linux/20250509-topics-tyr-platform_iomem-v8-0-e9f1725a40da@collabora.com/
[2] - https://lore.kernel.org/all/20250609-math-rust-v1-v1-1-285fac00031f@samsung.com/
[3] - https://github.com/mwilczy/linux/commits/rust-next-pwm-working-fan-for-sending-v7/

---
Changes in v3:
 - Addressed feedback from Uwe by making multiple changes to the TH1520
   driver and the abstraction layer.
 - Split the core PWM abstractions into three focused commits to ease
   review per Benno request.
 - Confirmed the driver now works correctly with CONFIG_PWM_DEBUG enabled
   by implementing the full waveform API, which correctly reads the
   hardware state.
 - Refactored the Rust code to build cleanly with
   CONFIG_RUST_BUILD_ASSERT_ALLOW=n, primarily by using the try_* family of
   functions for IoMem access.
 - Included several cosmetic changes and cleanups to the abstractions
   per Miguel review.

- Link to v2: https://lore.kernel.org/r/20250610-rust-next-pwm-working-fan-for-sending-v2-0-753e2955f110@samsung.com

Changes in v2:
 - Reworked the PWM abstraction layer based on extensive feedback.
 - Replaced initial devm allocation with a proper ARef<Chip> lifetime model
   using AlwaysRefCounted.
 - Implemented a Registration RAII guard to ensure safe chip add/remove.
 - Migrated the PwmOps trait from the legacy .apply callback to the modern
   waveform API.
 - Refactored the TH1520 driver to use the new, safer abstractions.
 - Added a patch to mark essential bus clocks as CLK_IGNORE_UNUSED to fix
   boot hangs when the PWM and thermal sensors are enabled.
- Link to v1: https://lore.kernel.org/r/20250524-rust-next-pwm-working-fan-for-sending-v1-0-bdd2d5094ff7@samsung.com

---
Michal Wilczynski (9):
      rust: pwm: Add Kconfig and basic data structures
      rust: pwm: Add core 'Device' and 'Chip' object wrappers
      rust: pwm: Add driver operations trait and registration support
      pwm: Add Rust driver for T-HEAD TH1520 SoC
      clk: thead: Mark essential bus clocks as CLK_IGNORE_UNUSED
      dt-bindings: pwm: thead: Add T-HEAD TH1520 PWM controller
      riscv: dts: thead: Add PWM controller node
      riscv: dts: thead: Add PVT node
      riscv: dts: thead: Add PWM fan and thermal control

 .../devicetree/bindings/pwm/thead,th1520-pwm.yaml  |  48 ++
 MAINTAINERS                                        |   8 +
 arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts  |  67 ++
 arch/riscv/boot/dts/thead/th1520.dtsi              |  18 +
 drivers/clk/thead/clk-th1520-ap.c                  |   5 +-
 drivers/pwm/Kconfig                                |  23 +
 drivers/pwm/Makefile                               |   1 +
 drivers/pwm/pwm_th1520.rs                          | 328 ++++++++
 rust/bindings/bindings_helper.h                    |   1 +
 rust/helpers/helpers.c                             |   1 +
 rust/kernel/lib.rs                                 |   2 +
 rust/kernel/pwm.rs                                 | 886 +++++++++++++++++++++
 12 files changed, 1386 insertions(+), 2 deletions(-)
---
base-commit: 79b01ff21368605a62b76535ab1ab5f1f726de60
change-id: 20250524-rust-next-pwm-working-fan-for-sending-552ad2d1b193

Best regards,
-- 
Michal Wilczynski <m.wilczynski@...sung.com>

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