Re: [PATCH v15 0/7] Rust Abstractions for PWM subsystem with TH1520 PWM driver

Michal Wilczynski
2025-10-13T10:24:25Z

On 9/30/25 14:20, Michal Wilczynski wrote:
> 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:
> - Expose static function pwmchip_release.
> - 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.
> - Device Tree Bindings & Nodes: The remaining patches add the necessary
> DT bindings and nodes for the TH1520 PWM controller, and the PWM fan
> configuration for the Lichee Pi 4A board.
>
> Testing:
> Tested on the TH1520 SoC. The fan works correctly. The duty/period
> calculations are correct. Fan starts slow when the chip is not hot and
> gradually increases the speed when PVT reports higher temperatures.
>
> The patches doesn't contain any dependencies that are not currently in
> the mainline kernel anymore.
>
> ---
> Changes in v15:
> - Update the TH1520 driver; read the hardware state directly instead of
> using state, fix an integer overflow using saturating arithmetic, and
> add handling zero period edge cases.
> - Add dbg prints, and also update them for using the preferred format
> for emiting a waveform.
> - Remove the consumer side Args wrapper from the abstraction layer.
> - Link to v14: https://lore.kernel.org/r/20250820-rust-next-pwm-working-fan-for-sending-v14-0-df2191621429@samsung.com
>

Hi Uwe,
Would you like me to re-base on v6.18-rc1 ?

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