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

[Alice Ryhl <aliceryhl@google.com>]

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>
---
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,
-- 
Alice Ryhl <aliceryhl@google.com>