linux-kernel - Re: [PATCH v10 0/7] Rust Abstractions for PWM subsystem with TH1520 PWM driver

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Message-ID: <ipvaegqlkco5qinhvn33mqvg7ev2walvs74xtzvhimxsfsfzhv@gcmpxcdtetdn>
Date: Thu, 10 Jul 2025 15:10:19 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: 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>, 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, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v10 0/7] Rust Abstractions for PWM subsystem with TH1520
 PWM driver

Hello,

On Thu, Jul 10, 2025 at 10:42:07AM +0200, Michal Wilczynski wrote:
> On 7/7/25 11:48, 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.

Is this really necessary? I didn't try to understand the requirements
yet, but I wonder about that. If you get the pwmchip from
__pwmchip_add() the right thing to do to release it is to call
pwmchip_remove(). Feels like a layer violation.

> [...]
> > ---
> > base-commit: 47753b5a1696283930a78aae79b29371f96f5bca

I have problems applying this series and don't have this base commit in
my repo.

Best regards
Uwe

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