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

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Message-ID: <aKYwgQBt62PyCEd9@archiso>
Date: Wed, 20 Aug 2025 20:30:57 +0000
From: Elle Rhumsaa <elle@...thered-steel.dev>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: 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>,
	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

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>
> ---
>  drivers/pwm/core.c  | 3 ++-
>  include/linux/pwm.h | 6 ++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 0d66376a83ec350e0c3718959f4d794efd71595a..a33da3dff608fdff91251e5fd07b0dbd295be022 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -1600,12 +1600,13 @@ void pwmchip_put(struct pwm_chip *chip)
>  }
>  EXPORT_SYMBOL_GPL(pwmchip_put);
>  
> -static void pwmchip_release(struct device *pwmchip_dev)
> +void pwmchip_release(struct device *pwmchip_dev)
>  {
>  	struct pwm_chip *chip = pwmchip_from_dev(pwmchip_dev);
>  
>  	kfree(chip);
>  }
> +EXPORT_SYMBOL_GPL(pwmchip_release);
>  
>  struct pwm_chip *pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv)
>  {
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 8cafc483db53addf95591d1ac74287532c0fa0ee..d86061024b52172edf3845bf9252a966f120e365 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -485,6 +485,12 @@ int __pwmchip_add(struct pwm_chip *chip, struct module *owner);
>  #define pwmchip_add(chip) __pwmchip_add(chip, THIS_MODULE)
>  void pwmchip_remove(struct pwm_chip *chip);
>  
> +/*
> + * For FFI wrapper use only:
> + * The Rust PWM abstraction needs this to properly free the pwm_chip.
> + */
> +void pwmchip_release(struct device *dev);
> +
>  int __devm_pwmchip_add(struct device *dev, struct pwm_chip *chip, struct module *owner);
>  #define devm_pwmchip_add(dev, chip) __devm_pwmchip_add(dev, chip, THIS_MODULE)
>  
> 
> -- 
> 2.34.1

Reviewed-by: Elle Rhumsaa <elle@...thered-steel.dev>