linux-kernel - Re: [PATCH v14 1/7] pwm: Export `pwmchip

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Message-ID: <3jxl6gpxwv376ooyny7qkeokeh7nzafttbyoehmwqzrccn5oip@747v6zdnogso>
Date: Mon, 15 Sep 2025 12:00:14 +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>, Daniel Almeida <daniel.almeida@...labora.com>, 
	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
Subject: Re: [PATCH v14 1/7] pwm: Export `pwmchip_release` for external use

Hello,

On Wed, Aug 20, 2025 at 10:35:36AM +0200, Michal Wilczynski wrote:
> The upcoming Rust abstraction layer for the PWM subsystem uses a custom
> `dev->release` handler to safely manage the lifetime of its driver
> data.
> 
> To prevent leaking the memory of the `struct pwm_chip` (allocated by
> `pwmchip_alloc`), this custom handler must also call the original
> `pwmchip_release` function to complete the cleanup.
> 
> Make `pwmchip_release` a global, exported function so that it can be
> called from the Rust FFI bridge. This involves removing the `static`
> keyword, adding a prototype to the public header, and exporting the
> symbol.
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@...sung.com>

I still somewhat dislike this patch. Isn't it possible to make the rust
abstraction use the pointer that .release is set to when it calls
pwmchip_alloc()?

(I wouldn't further delay this series for this discussion, this can be
handled just fine at a later point in time.)

Best regards
Uwe

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