Message-ID: <3f9ab01c-470e-48b5-a309-71325ecc4906@samsung.com>
Date: Wed, 22 Oct 2025 10:34:42 +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>, 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>,
	Drew Fustini <fustini@...nel.org>, Daniel Almeida
	<daniel.almeida@...labora.com>
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, Elle Rhumsaa <elle@...thered-steel.dev>,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v16 0/7] Rust Abstractions for PWM subsystem with TH1520
 PWM driver



On 10/16/25 15:38, 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, 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 v16:
> - Re-base on top of 6.18-rc1.
> - Make RUST_PWM_ABSTRACTIONS an invisible Kconfig option and remove the
>   redundant depends on PWM=y.
> - Handle period requests that are too small by rounding up to 1 cycle,
>   rather than disabling the PWM.
> - Correctly report a status of 1 to indicate when the period has been
>   rounded up.
> - Change the error code for an unsupported high clock rate from ERANGE
>   to EINVAL for consistency.
> - Link to v15: https://lore.kernel.org/r/20250930-rust-next-pwm-working-fan-for-sending-v15-0-5661c3090877@samsung.com
> 

Hi Uwe,

Since you mentioned last time that you were happy with the code, would
you please consider picking up this series for linux-next? It would be
great to get it in for wider testing to ensure everything is solid.

On a related note, it looks like Clk is getting Send and Sync traits
[1], which is excellent news! This will allow the TH1520 PWM driver to
be 100% safe Rust :-).

I recall you prefer to base your pull requests on -rc1. With that in
mind, I plan to send a follow up patch to remove the unsafe block for
the Clk handling after the next merge window closes.

[1] - https://lore.kernel.org/all/20251020-clk-send-sync-v2-0-44ab533ae084@google.com/T/#mdfdfa9947b4d51b9ebc6d667911bf19907761655


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

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