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Thu, 27 Nov 2025 18:15:03 +0100 (CET) From: Markus Probst Date: Thu, 27 Nov 2025 17:15:06 +0000 Subject: [PATCH] Move pwm registration into pwm::Chip::new Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251127-pwm_safe_register-v1-1-d22d0ed068ac@posteo.de> X-B4-Tracking: v=1; b=H4sIAAeHKGkC/6tWKk4tykwtVrJSqFYqSi3LLM7MzwNyDHUUlJIzE vPSU3UzU4B8JSMDI1NDQyNz3YLy3PjixLTU+KLU9MziktQi3VQTyySDRCMzQ0MDQyWgvoKi1LT MCrCZ0bG1tQDN9qaZYwAAAA== X-Change-ID: 20251127-pwm_safe_register-e49b0a261101 To: Drew Fustini , Guo Ren , Fu Wei , =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , Michal Wilczynski , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich Cc: linux-riscv@lists.infradead.org, linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, Markus Probst X-Developer-Signature: v=1; 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preference=encrypt The `pwm::Registration::register` function provides no guarantee that the function isn't called twice with the same pwm chip, which is considered unsafe. Add the code responsible for the registration into `pwm::Chip::new`. The registration will happen before the driver gets access to the refcounted pwm chip and can therefore guarantee that the registration isn't called twice on the same pwm chip. Signed-off-by: Markus Probst Reviewed-by: Daniel Almeida --- This patch provides the additional guarantee that the pwm chip doesn't get registered twice. The following changes were made: - change the visibility of `pwm::Registration` to private - remove the `pwm::Registration::register` function - add code for registering the pwm chip in `pwm::Chip::new` - add Send + Sync bounds to `PwmOps` Note that I wasn't able to test this patch, due to the lack of hardware. --- drivers/pwm/pwm_th1520.rs | 4 +--- rust/kernel/pwm.rs | 53 ++++++++++++++++++-------------------------= ---- 2 files changed, 21 insertions(+), 36 deletions(-) diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs index 955c359b07fb..1919b5a1f69e 100644 --- a/drivers/pwm/pwm_th1520.rs +++ b/drivers/pwm/pwm_th1520.rs @@ -363,7 +363,7 @@ fn probe( return Err(EINVAL); } =20 - let chip =3D pwm::Chip::new( + pwm::Chip::new( dev, TH1520_MAX_PWM_NUM, try_pin_init!(Th1520PwmDriverData { @@ -372,8 +372,6 @@ fn probe( }), )?; =20 - pwm::Registration::register(dev, chip)?; - Ok(KBox::new(Th1520PwmPlatformDriver, GFP_KERNEL)?.into()) } } diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs index cb00f8a8765c..c5d03ee8bc95 100644 --- a/rust/kernel/pwm.rs +++ b/rust/kernel/pwm.rs @@ -173,7 +173,7 @@ pub struct RoundedWaveform { } =20 /// Trait defining the operations for a PWM driver. -pub trait PwmOps: 'static + Sized { +pub trait PwmOps: 'static + Send + Sync + Sized { /// The driver-specific hardware representation of a waveform. /// /// This type must be [`Copy`], [`Default`], and fit within `PWM_WFHWS= IZE`. @@ -585,7 +585,7 @@ unsafe fn bound_parent_device(&self) -> &device::Device= { /// Returns an [`ARef`] managing the chip's lifetime via refcoun= ting /// on its embedded `struct device`. pub fn new( - parent_dev: &device::Device, + parent_dev: &device::Device, num_channels: u32, data: impl pin_init::PinInit, ) -> Result> { @@ -623,7 +623,21 @@ pub fn new( // SAFETY: `chip_ptr_as_self` points to a valid `Chip` (layout-com= patible with // `bindings::pwm_chip`) whose embedded device has refcount 1. // `ARef::from_raw` takes this pointer and manages it via `AlwaysR= efCounted`. - Ok(unsafe { ARef::from_raw(NonNull::new_unchecked(chip_ptr_as_self= )) }) + let chip =3D unsafe { ARef::from_raw(NonNull::new_unchecked(chip_p= tr_as_self)) }; + + // SAFETY: `c_chip_ptr` points to a valid chip with its ops initia= lized. + // `__pwmchip_add` is the C function to register the chip with the= PWM core. + unsafe { + to_result(bindings::__pwmchip_add(c_chip_ptr, core::ptr::null_= mut()))?; + } + + let registration =3D Registration { + chip: ARef::clone(&chip), + }; + + devres::register(parent_dev, registration, GFP_KERNEL)?; + + Ok(chip) } } =20 @@ -654,50 +668,23 @@ unsafe fn dec_ref(obj: NonNull>) { // structure's state is managed and synchronized by the kernel's device mo= del // and PWM core locking mechanisms. Therefore, it is safe to move the `Chi= p` // wrapper (and the pointer it contains) across threads. -unsafe impl Send for Chip {} +unsafe impl Send for Chip {} =20 // SAFETY: It is safe for multiple threads to have shared access (`&Chip`)= because // the `Chip` data is immutable from the Rust side without holding the app= ropriate // kernel locks, which the C core is responsible for. Any interior mutabil= ity is // handled and synchronized by the C kernel code. -unsafe impl Sync for Chip {} +unsafe impl Sync for Chip {} =20 /// A resource guard that ensures `pwmchip_remove` is called on drop. /// /// This struct is intended to be managed by the `devres` framework by tra= nsferring its ownership /// via [`devres::register`]. This ties the lifetime of the PWM chip regis= tration /// to the lifetime of the underlying device. -pub struct Registration { +struct Registration { chip: ARef>, } =20 -impl Registration { - /// Registers a PWM chip with the PWM subsystem. - /// - /// Transfers its ownership to the `devres` framework, which ties its = lifetime - /// to the parent device. - /// On unbind of the parent device, the `devres` entry will be dropped= , automatically - /// calling `pwmchip_remove`. This function should be called from the = driver's `probe`. - pub fn register(dev: &device::Device, chip: ARef>) -> R= esult { - let chip_parent =3D chip.device().parent().ok_or(EINVAL)?; - if dev.as_raw() !=3D chip_parent.as_raw() { - return Err(EINVAL); - } - - let c_chip_ptr =3D chip.as_raw(); - - // SAFETY: `c_chip_ptr` points to a valid chip with its ops initia= lized. - // `__pwmchip_add` is the C function to register the chip with the= PWM core. - unsafe { - to_result(bindings::__pwmchip_add(c_chip_ptr, core::ptr::null_= mut()))?; - } - - let registration =3D Registration { chip }; - - devres::register(dev, registration, GFP_KERNEL) - } -} - impl Drop for Registration { fn drop(&mut self) { let chip_raw =3D self.chip.as_raw(); --- base-commit: fae00ea9f00367771003ace78f29549dead58fc7 change-id: 20251127-pwm_safe_register-e49b0a261101