[PATCH v2] 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.

[1]: https://lore.kernel.org/all/20250810-topics-tyr-request_irq2-v8-0-8163f4c4c3a6@collabora.com/
---
Changes in v2:
- Rebase on v8 of [1] (and hence v6.17-rc1).
- Link to v1: https://lore.kernel.org/r/20250721-irq-bound-device-v1-1-4fb2af418a63@google.com
---
 rust/kernel/irq/request.rs | 85 ++++++++++++++++++++++++++--------------------
 1 file changed, 49 insertions(+), 36 deletions(-)

diff --git a/rust/kernel/irq/request.rs b/rust/kernel/irq/request.rs
index 29597573e91106d0990ec096a8e7f93ef2f89f2b..ae5d967fb9d6a748b4274464b615e6dd965bca10 100644
--- a/rust/kernel/irq/request.rs
+++ b/rust/kernel/irq/request.rs
@@ -36,18 +36,18 @@ 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)
     }
 }
 
@@ -140,7 +140,7 @@ pub fn irq(&self) -> u32 {
 ///
 /// ```
 /// # use kernel::c_str;
-/// # use kernel::device::Bound;
+/// # use kernel::device::{Bound, Device};
 /// # use kernel::irq::{self, Flags, IrqRequest, IrqReturn, Registration};
 /// # use kernel::prelude::*;
 /// # use kernel::sync::{Arc, Completion};
@@ -153,7 +153,7 @@ pub fn irq(&self) -> u32 {
 ///
 /// impl irq::Handler for Handler {
 ///     // Executed in IRQ context.
-///     fn handle(&self) -> IrqReturn {
+///     fn handle(&self, _dev: &Device<Bound>) -> IrqReturn {
 ///         self.completion.complete_all();
 ///         IrqReturn::Handled
 ///     }
@@ -179,7 +179,7 @@ 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]
@@ -207,8 +207,8 @@ 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.
@@ -221,7 +221,7 @@ 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
@@ -258,9 +258,13 @@ 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`].
@@ -286,7 +290,8 @@ pub trait ThreadedHandler: Sync {
     /// handler, i.e. [`ThreadedHandler::handle_threaded`].
     ///
     /// The default implementation returns [`ThreadedIrqReturn::WakeThread`].
-    fn handle(&self) -> ThreadedIrqReturn {
+    #[expect(unused_variables)]
+    fn handle(&self, device: &Device<Bound>) -> ThreadedIrqReturn {
         ThreadedIrqReturn::WakeThread
     }
 
@@ -294,26 +299,26 @@ fn handle(&self) -> ThreadedIrqReturn {
     ///
     /// 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)
     }
 }
 
@@ -332,7 +337,7 @@ fn handle_threaded(&self) -> IrqReturn {
 ///
 /// ```
 /// # use kernel::c_str;
-/// # use kernel::device::Bound;
+/// # use kernel::device::{Bound, Device};
 /// # use kernel::irq::{
 /// #   self, Flags, IrqRequest, IrqReturn, ThreadedHandler, ThreadedIrqReturn,
 /// #   ThreadedRegistration,
@@ -355,7 +360,7 @@ fn handle_threaded(&self) -> IrqReturn {
 ///     // This will run (in a separate kthread) if and only if
 ///     // [`ThreadedHandler::handle`] returns [`WakeThread`], which it does by
 ///     // default.
-///     fn handle_threaded(&self) -> IrqReturn {
+///     fn handle_threaded(&self, _dev: &Device<Bound>) -> IrqReturn {
 ///         let mut data = self.value.lock();
 ///         *data += 1;
 ///         IrqReturn::Handled
@@ -388,7 +393,7 @@ 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]
@@ -416,8 +421,8 @@ 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.
@@ -431,7 +436,7 @@ pub fn new<'a>(
                                 Some(thread_fn_callback::<T>),
                                 flags.into_inner(),
                                 name.as_char_ptr(),
-                                (&raw mut (*this.as_ptr()).handler).cast(),
+                                this.as_ptr().cast::<c_void>(),
                             )
                         })?;
                         request.irq
@@ -471,16 +476,24 @@ 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: 062b3e4a1f880f104a8d4b90b767788786aa7b78
change-id: 20250721-irq-bound-device-c9fdbfdd8cd9
prerequisite-change-id: 20250712-topics-tyr-request_irq2-ae7ee9b85854:v8
prerequisite-patch-id: 0ed57dd6c685034df8a741c0290e1647880ad9b9
prerequisite-patch-id: 939809f0395089541acb9421cdb798ea625bd31b
prerequisite-patch-id: 5106394e817b371de5035a8289f6820f8aea3895
prerequisite-patch-id: 402fb2b44076d5a5d2a7210a8496e665d05e7c2a
prerequisite-patch-id: c4d08dda330b2ae8b5c8bb7a9d6bdef379119a6d
prerequisite-patch-id: 0a639274db9c6e7002828a6652a9f5a7d1dfd67f

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