[PATCH v10 0/7] Rust Abstractions for PWM subsystem with TH1520 PWM driver

[Uwe Kleine-König]

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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