Re: [PATCH v15 1/7] pwm: Export `pwmchip_release` for external use

Elle Rhumsaa
2025-10-01T20:51:39Z

On Tue, Sep 30, 2025 at 02:20:32PM +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.
>
> Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.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