Re: [PATCH] rust: irq: add &Device<Bound> argument to irq callbacks

[Dirk Behme <dirk.behme@de.bosch.com>]

On 21/07/2025 16:38, Alice Ryhl wrote:
> When working with a bus device, many operations are only possible while
> the device is still bound. The &Device<Bound> type represents a proof in
> the type system that you are in a scope where the device is guaranteed
> to still be bound. Since we deregister irq callbacks when unbinding a
> device, if an irq callback is running, that implies that the device has
> not yet been unbound.
> 
> To allow drivers to take advantage of that, add an additional argument
> to irq callbacks.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>


With

https://lore.kernel.org/rust-for-linux/dd34e5f4-5027-4096-9f32-129c8a067d0a@de.bosch.com/

let me add

Tested-by: Dirk Behme <dirk.behme@de.bosch.com>

here as well.

Thanks!

Dirk


> ---
> This patch is a follow-up to Daniel's irq series [1] that adds a
> &Device<Bound> argument to all irq callbacks. This allows you to use
> operations that are only safe on a bound device inside an irq callback.
> 
> The patch is otherwise based on top of driver-core-next.
> 
> [1]: https://lore.kernel.org/r/20250715-topics-tyr-request_irq2-v7-0-d469c0f37c07@collabora.com
> ---
>  rust/kernel/irq/request.rs | 88 ++++++++++++++++++++++++++--------------------
>  1 file changed, 49 insertions(+), 39 deletions(-)
> 
> diff --git a/rust/kernel/irq/request.rs b/rust/kernel/irq/request.rs
> index d070ddabd37e7806f76edefd5d2ad46524be620e..f99aff2dd479f5223c90f0d2694f57e6c864bdb5 100644
> --- a/rust/kernel/irq/request.rs
> +++ b/rust/kernel/irq/request.rs
> @@ -37,18 +37,18 @@ pub trait Handler: Sync {
>      /// All work that does not necessarily need to be executed from
>      /// interrupt context, should be deferred to a threaded handler.
>      /// See also [`ThreadedRegistration`].
> -    fn handle(&self) -> IrqReturn;
> +    fn handle(&self, device: &Device<Bound>) -> IrqReturn;
>  }
>  
>  impl<T: ?Sized + Handler + Send> Handler for Arc<T> {
> -    fn handle(&self) -> IrqReturn {
> -        T::handle(self)
> +    fn handle(&self, device: &Device<Bound>) -> IrqReturn {
> +        T::handle(self, device)
>      }
>  }
>  
>  impl<T: ?Sized + Handler, A: Allocator> Handler for Box<T, A> {
> -    fn handle(&self) -> IrqReturn {
> -        T::handle(self)
> +    fn handle(&self, device: &Device<Bound>) -> IrqReturn {
> +        T::handle(self, device)
>      }
>  }
>  
> @@ -134,7 +134,7 @@ pub fn irq(&self) -> u32 {
>  /// use core::sync::atomic::Ordering;
>  ///
>  /// use kernel::prelude::*;
> -/// use kernel::device::Bound;
> +/// use kernel::device::{Bound, Device};
>  /// use kernel::irq::flags::Flags;
>  /// use kernel::irq::Registration;
>  /// use kernel::irq::IrqRequest;
> @@ -156,7 +156,7 @@ pub fn irq(&self) -> u32 {
>  /// impl kernel::irq::request::Handler for Handler {
>  ///     // This is executing in IRQ context in some CPU. Other CPUs can still
>  ///     // try to access to data.
> -///     fn handle(&self) -> IrqReturn {
> +///     fn handle(&self, _dev: &Device<Bound>) -> IrqReturn {
>  ///         self.0.fetch_add(1, Ordering::Relaxed);
>  ///
>  ///         IrqReturn::Handled
> @@ -182,8 +182,7 @@ pub fn irq(&self) -> u32 {
>  ///
>  /// # Invariants
>  ///
> -/// * We own an irq handler using `&self.handler` as its private data.
> -///
> +/// * We own an irq handler whose cookie is a pointer to `Self`.
>  #[pin_data]
>  pub struct Registration<T: Handler + 'static> {
>      #[pin]
> @@ -211,8 +210,8 @@ pub fn new<'a>(
>              inner <- Devres::new(
>                  request.dev,
>                  try_pin_init!(RegistrationInner {
> -                    // SAFETY: `this` is a valid pointer to the `Registration` instance
> -                    cookie: unsafe { &raw mut (*this.as_ptr()).handler }.cast(),
> +                    // INVARIANT: `this` is a valid pointer to the `Registration` instance
> +                    cookie: this.as_ptr().cast::<c_void>(),
>                      irq: {
>                          // SAFETY:
>                          // - The callbacks are valid for use with request_irq.
> @@ -225,7 +224,7 @@ pub fn new<'a>(
>                                  Some(handle_irq_callback::<T>),
>                                  flags.into_inner(),
>                                  name.as_char_ptr(),
> -                                (&raw mut (*this.as_ptr()).handler).cast(),
> +                                this.as_ptr().cast::<c_void>(),
>                              )
>                          })?;
>                          request.irq
> @@ -262,9 +261,13 @@ pub fn synchronize(&self, dev: &Device<Bound>) -> Result {
>  ///
>  /// This function should be only used as the callback in `request_irq`.
>  unsafe extern "C" fn handle_irq_callback<T: Handler>(_irq: i32, ptr: *mut c_void) -> c_uint {
> -    // SAFETY: `ptr` is a pointer to T set in `Registration::new`
> -    let handler = unsafe { &*(ptr as *const T) };
> -    T::handle(handler) as c_uint
> +    // SAFETY: `ptr` is a pointer to `Registration<T>` set in `Registration::new`
> +    let registration = unsafe { &*(ptr as *const Registration<T>) };
> +    // SAFETY: The irq callback is removed before the device is unbound, so the fact that the irq
> +    // callback is running implies that the device has not yet been unbound.
> +    let device = unsafe { registration.inner.device().as_bound() };
> +
> +    T::handle(&registration.handler, device) as c_uint
>  }
>  
>  /// The value that can be returned from `ThreadedHandler::handle_irq`.
> @@ -288,32 +291,32 @@ pub trait ThreadedHandler: Sync {
>      /// limitations do apply. All work that does not necessarily need to be
>      /// executed from interrupt context, should be deferred to the threaded
>      /// handler, i.e. [`ThreadedHandler::handle_threaded`].
> -    fn handle(&self) -> ThreadedIrqReturn;
> +    fn handle(&self, device: &Device<Bound>) -> ThreadedIrqReturn;
>  
>      /// The threaded IRQ handler.
>      ///
>      /// This is executed in process context. The kernel creates a dedicated
>      /// kthread for this purpose.
> -    fn handle_threaded(&self) -> IrqReturn;
> +    fn handle_threaded(&self, device: &Device<Bound>) -> IrqReturn;
>  }
>  
>  impl<T: ?Sized + ThreadedHandler + Send> ThreadedHandler for Arc<T> {
> -    fn handle(&self) -> ThreadedIrqReturn {
> -        T::handle(self)
> +    fn handle(&self, device: &Device<Bound>) -> ThreadedIrqReturn {
> +        T::handle(self, device)
>      }
>  
> -    fn handle_threaded(&self) -> IrqReturn {
> -        T::handle_threaded(self)
> +    fn handle_threaded(&self, device: &Device<Bound>) -> IrqReturn {
> +        T::handle_threaded(self, device)
>      }
>  }
>  
>  impl<T: ?Sized + ThreadedHandler, A: Allocator> ThreadedHandler for Box<T, A> {
> -    fn handle(&self) -> ThreadedIrqReturn {
> -        T::handle(self)
> +    fn handle(&self, device: &Device<Bound>) -> ThreadedIrqReturn {
> +        T::handle(self, device)
>      }
>  
> -    fn handle_threaded(&self) -> IrqReturn {
> -        T::handle_threaded(self)
> +    fn handle_threaded(&self, device: &Device<Bound>) -> IrqReturn {
> +        T::handle_threaded(self, device)
>      }
>  }
>  
> @@ -334,7 +337,7 @@ fn handle_threaded(&self) -> IrqReturn {
>  /// use core::sync::atomic::Ordering;
>  ///
>  /// use kernel::prelude::*;
> -/// use kernel::device::Bound;
> +/// use kernel::device::{Bound, Device};
>  /// use kernel::irq::flags::Flags;
>  /// use kernel::irq::ThreadedIrqReturn;
>  /// use kernel::irq::ThreadedRegistration;
> @@ -356,7 +359,7 @@ fn handle_threaded(&self) -> IrqReturn {
>  /// impl kernel::irq::request::ThreadedHandler for Handler {
>  ///     // This is executing in IRQ context in some CPU. Other CPUs can still
>  ///     // try to access the data.
> -///     fn handle(&self) -> ThreadedIrqReturn {
> +///     fn handle(&self, _dev: &Device<Bound>) -> ThreadedIrqReturn {
>  ///         self.0.fetch_add(1, Ordering::Relaxed);
>  ///         // By returning `WakeThread`, we indicate to the system that the
>  ///         // thread function should be called. Otherwise, return
> @@ -366,7 +369,7 @@ fn handle_threaded(&self) -> IrqReturn {
>  ///
>  ///     // This will run (in a separate kthread) if and only if `handle`
>  ///     // returns `WakeThread`.
> -///     fn handle_threaded(&self) -> IrqReturn {
> +///     fn handle_threaded(&self, _dev: &Device<Bound>) -> IrqReturn {
>  ///         self.0.fetch_add(1, Ordering::Relaxed);
>  ///         IrqReturn::Handled
>  ///     }
> @@ -391,8 +394,7 @@ fn handle_threaded(&self) -> IrqReturn {
>  ///
>  /// # Invariants
>  ///
> -/// * We own an irq handler using `&T` as its private data.
> -///
> +/// * We own an irq handler whose cookie is a pointer to `Self`.
>  #[pin_data]
>  pub struct ThreadedRegistration<T: ThreadedHandler + 'static> {
>      #[pin]
> @@ -420,8 +422,8 @@ pub fn new<'a>(
>              inner <- Devres::new(
>                  request.dev,
>                  try_pin_init!(RegistrationInner {
> -                    // SAFETY: `this` is a valid pointer to the `ThreadedRegistration` instance.
> -                    cookie: unsafe { &raw mut (*this.as_ptr()).handler }.cast(),
> +                    // INVARIANT: `this` is a valid pointer to the `ThreadedRegistration` instance.
> +                    cookie: this.as_ptr().cast::<c_void>(),
>                      irq: {
>                          // SAFETY:
>                          // - The callbacks are valid for use with request_threaded_irq.
> @@ -435,7 +437,7 @@ pub fn new<'a>(
>                                  Some(thread_fn_callback::<T>),
>                                  flags.into_inner() as usize,
>                                  name.as_char_ptr(),
> -                                (&raw mut (*this.as_ptr()).handler).cast(),
> +                                this.as_ptr().cast::<c_void>(),
>                              )
>                          })?;
>                          request.irq
> @@ -475,16 +477,24 @@ pub fn synchronize(&self, dev: &Device<Bound>) -> Result {
>      _irq: i32,
>      ptr: *mut c_void,
>  ) -> c_uint {
> -    // SAFETY: `ptr` is a pointer to T set in `ThreadedRegistration::new`
> -    let handler = unsafe { &*(ptr as *const T) };
> -    T::handle(handler) as c_uint
> +    // SAFETY: `ptr` is a pointer to `ThreadedRegistration<T>` set in `ThreadedRegistration::new`
> +    let registration = unsafe { &*(ptr as *const ThreadedRegistration<T>) };
> +    // SAFETY: The irq callback is removed before the device is unbound, so the fact that the irq
> +    // callback is running implies that the device has not yet been unbound.
> +    let device = unsafe { registration.inner.device().as_bound() };
> +
> +    T::handle(&registration.handler, device) as c_uint
>  }
>  
>  /// # Safety
>  ///
>  /// This function should be only used as the callback in `request_threaded_irq`.
>  unsafe extern "C" fn thread_fn_callback<T: ThreadedHandler>(_irq: i32, ptr: *mut c_void) -> c_uint {
> -    // SAFETY: `ptr` is a pointer to T set in `ThreadedRegistration::new`
> -    let handler = unsafe { &*(ptr as *const T) };
> -    T::handle_threaded(handler) as c_uint
> +    // SAFETY: `ptr` is a pointer to `ThreadedRegistration<T>` set in `ThreadedRegistration::new`
> +    let registration = unsafe { &*(ptr as *const ThreadedRegistration<T>) };
> +    // SAFETY: The irq callback is removed before the device is unbound, so the fact that the irq
> +    // callback is running implies that the device has not yet been unbound.
> +    let device = unsafe { registration.inner.device().as_bound() };
> +
> +    T::handle_threaded(&registration.handler, device) as c_uint
>  }
> 
> ---
> base-commit: d860d29e91be18de62b0f441edee7d00f6cb4972
> change-id: 20250721-irq-bound-device-c9fdbfdd8cd9
> 
> Best regards,