rust: irq: add support for non-threaded IRQs and handlers

This patch adds support for non-threaded IRQs and handlers through
irq::Registration and the irq::Handler trait.

Registering an irq is dependent upon having a IrqRequest that was
previously allocated by a given device. This will be introduced in
subsequent patches.

Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250811-topics-tyr-request_irq2-v9-3-0485dcd9bcbf@collabora.com
[ Remove expect(dead_code) from Flags::into_inner(), add
  expect(dead_code) to IrqRequest::new(), fix intra-doc links. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

2 files changed, 266 insertions, 2 deletions

diff --git a/rust/kernel/irq/flags.rs b/rust/kernel/irq/flags.rs
index d769d68e8edc..adfde96ec47c 100644
--- a/rust/kernel/irq/flags.rs
+++ b/rust/kernel/irq/flags.rs
@@ -21,7 +21,7 @@ use crate::prelude::*;
 /// If an invalid combination of flags is provided, the system will refuse to
 /// register the handler, and lower layers will enforce certain flags when
 /// necessary. This means, for example, that all the
-/// `crate::irq::Registration` for a shared interrupt have to agree on
+/// [`crate::irq::Registration`] for a shared interrupt have to agree on
 /// [`Flags::SHARED`] and on the same trigger type, if set.
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub struct Flags(c_ulong);
@@ -92,7 +92,6 @@ impl Flags {
     /// `PERCPU`.
     pub const NO_DEBUG: Flags = Flags::new(bindings::IRQF_NO_DEBUG);
 
-    #[expect(dead_code)]
     pub(crate) fn into_inner(self) -> c_ulong {
         self.0
     }
diff --git a/rust/kernel/irq/request.rs b/rust/kernel/irq/request.rs
new file mode 100644
index 000000000000..c585811cfdfb
--- /dev/null
+++ b/rust/kernel/irq/request.rs
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright 2025 Collabora ltd.
+
+//! This module provides types like [`Registration`] which allow users to
+//! register handlers for a given IRQ line.
+
+use core::marker::PhantomPinned;
+
+use crate::alloc::Allocator;
+use crate::device::{Bound, Device};
+use crate::devres::Devres;
+use crate::error::to_result;
+use crate::irq::flags::Flags;
+use crate::prelude::*;
+use crate::str::CStr;
+use crate::sync::Arc;
+
+/// The value that can be returned from a [`Handler`] or a `ThreadedHandler`.
+#[repr(u32)]
+pub enum IrqReturn {
+    /// The interrupt was not from this device or was not handled.
+    None = bindings::irqreturn_IRQ_NONE,
+
+    /// The interrupt was handled by this device.
+    Handled = bindings::irqreturn_IRQ_HANDLED,
+}
+
+/// Callbacks for an IRQ handler.
+pub trait Handler: Sync {
+    /// The hard IRQ handler.
+    ///
+    /// This is executed in interrupt context, hence all corresponding
+    /// limitations do apply.
+    ///
+    /// 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;
+}
+
+impl<T: ?Sized + Handler + Send> Handler for Arc<T> {
+    fn handle(&self) -> IrqReturn {
+        T::handle(self)
+    }
+}
+
+impl<T: ?Sized + Handler, A: Allocator> Handler for Box<T, A> {
+    fn handle(&self) -> IrqReturn {
+        T::handle(self)
+    }
+}
+
+/// # Invariants
+///
+/// - `self.irq` is the same as the one passed to `request_{threaded}_irq`.
+/// - `cookie` was passed to `request_{threaded}_irq` as the cookie. It is guaranteed to be unique
+///   by the type system, since each call to `new` will return a different instance of
+///   `Registration`.
+#[pin_data(PinnedDrop)]
+struct RegistrationInner {
+    irq: u32,
+    cookie: *mut c_void,
+}
+
+impl RegistrationInner {
+    fn synchronize(&self) {
+        // SAFETY: safe as per the invariants of `RegistrationInner`
+        unsafe { bindings::synchronize_irq(self.irq) };
+    }
+}
+
+#[pinned_drop]
+impl PinnedDrop for RegistrationInner {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY:
+        //
+        // Safe as per the invariants of `RegistrationInner` and:
+        //
+        // - The containing struct is `!Unpin` and was initialized using
+        // pin-init, so it occupied the same memory location for the entirety of
+        // its lifetime.
+        //
+        // Notice that this will block until all handlers finish executing,
+        // i.e.: at no point will &self be invalid while the handler is running.
+        unsafe { bindings::free_irq(self.irq, self.cookie) };
+    }
+}
+
+// SAFETY: We only use `inner` on drop, which called at most once with no
+// concurrent access.
+unsafe impl Sync for RegistrationInner {}
+
+// SAFETY: It is safe to send `RegistrationInner` across threads.
+unsafe impl Send for RegistrationInner {}
+
+/// A request for an IRQ line for a given device.
+///
+/// # Invariants
+///
+/// - `ìrq` is the number of an interrupt source of `dev`.
+/// - `irq` has not been registered yet.
+pub struct IrqRequest<'a> {
+    dev: &'a Device<Bound>,
+    irq: u32,
+}
+
+impl<'a> IrqRequest<'a> {
+    /// Creates a new IRQ request for the given device and IRQ number.
+    ///
+    /// # Safety
+    ///
+    /// - `irq` should be a valid IRQ number for `dev`.
+    #[expect(dead_code)]
+    pub(crate) unsafe fn new(dev: &'a Device<Bound>, irq: u32) -> Self {
+        // INVARIANT: `irq` is a valid IRQ number for `dev`.
+        IrqRequest { dev, irq }
+    }
+
+    /// Returns the IRQ number of an [`IrqRequest`].
+    pub fn irq(&self) -> u32 {
+        self.irq
+    }
+}
+
+/// A registration of an IRQ handler for a given IRQ line.
+///
+/// # Examples
+///
+/// The following is an example of using `Registration`. It uses a
+/// [`Completion`] to coordinate between the IRQ
+/// handler and process context. [`Completion`] uses interior mutability, so the
+/// handler can signal with [`Completion::complete_all()`] and the process
+/// context can wait with [`Completion::wait_for_completion()`] even though
+/// there is no way to get a mutable reference to the any of the fields in
+/// `Data`.
+///
+/// [`Completion`]: kernel::sync::Completion
+/// [`Completion::complete_all()`]: kernel::sync::Completion::complete_all
+/// [`Completion::wait_for_completion()`]: kernel::sync::Completion::wait_for_completion
+///
+/// ```
+/// use kernel::c_str;
+/// use kernel::device::Bound;
+/// use kernel::irq::{self, Flags, IrqRequest, IrqReturn, Registration};
+/// use kernel::prelude::*;
+/// use kernel::sync::{Arc, Completion};
+///
+/// // Data shared between process and IRQ context.
+/// #[pin_data]
+/// struct Data {
+///     #[pin]
+///     completion: Completion,
+/// }
+///
+/// impl irq::Handler for Data {
+///     // Executed in IRQ context.
+///     fn handle(&self) -> IrqReturn {
+///         self.completion.complete_all();
+///         IrqReturn::Handled
+///     }
+/// }
+///
+/// // Registers an IRQ handler for the given IrqRequest.
+/// //
+/// // This runs in process context and assumes `request` was previously acquired from a device.
+/// fn register_irq(
+///     handler: impl PinInit<Data, Error>,
+///     request: IrqRequest<'_>,
+/// ) -> Result<Arc<Registration<Data>>> {
+///     let registration = Registration::new(request, Flags::SHARED, c_str!("my_device"), handler);
+///
+///     let registration = Arc::pin_init(registration, GFP_KERNEL)?;
+///
+///     registration.handler().completion.wait_for_completion();
+///
+///     Ok(registration)
+/// }
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// # Invariants
+///
+/// * We own an irq handler using `&self.handler` as its private data.
+#[pin_data]
+pub struct Registration<T: Handler + 'static> {
+    #[pin]
+    inner: Devres<RegistrationInner>,
+
+    #[pin]
+    handler: T,
+
+    /// Pinned because we need address stability so that we can pass a pointer
+    /// to the callback.
+    #[pin]
+    _pin: PhantomPinned,
+}
+
+impl<T: Handler + 'static> Registration<T> {
+    /// Registers the IRQ handler with the system for the given IRQ number.
+    pub fn new<'a>(
+        request: IrqRequest<'a>,
+        flags: Flags,
+        name: &'static CStr,
+        handler: impl PinInit<T, Error> + 'a,
+    ) -> impl PinInit<Self, Error> + 'a {
+        try_pin_init!(&this in Self {
+            handler <- handler,
+            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(),
+                    irq: {
+                        // SAFETY:
+                        // - The callbacks are valid for use with request_irq.
+                        // - If this succeeds, the slot is guaranteed to be valid until the
+                        //   destructor of Self runs, which will deregister the callbacks
+                        //   before the memory location becomes invalid.
+                        to_result(unsafe {
+                            bindings::request_irq(
+                                request.irq,
+                                Some(handle_irq_callback::<T>),
+                                flags.into_inner(),
+                                name.as_char_ptr(),
+                                (&raw mut (*this.as_ptr()).handler).cast(),
+                            )
+                        })?;
+                        request.irq
+                    }
+                })
+            ),
+            _pin: PhantomPinned,
+        })
+    }
+
+    /// Returns a reference to the handler that was registered with the system.
+    pub fn handler(&self) -> &T {
+        &self.handler
+    }
+
+    /// Wait for pending IRQ handlers on other CPUs.
+    ///
+    /// This will attempt to access the inner [`Devres`] container.
+    pub fn try_synchronize(&self) -> Result {
+        let inner = self.inner.try_access().ok_or(ENODEV)?;
+        inner.synchronize();
+        Ok(())
+    }
+
+    /// Wait for pending IRQ handlers on other CPUs.
+    pub fn synchronize(&self, dev: &Device<Bound>) -> Result {
+        let inner = self.inner.access(dev)?;
+        inner.synchronize();
+        Ok(())
+    }
+}
+
+/// # Safety
+///
+/// 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
+}