[PATCH v7 3/6] rust: irq: add support for non-threaded IRQs and handlers

[Daniel Almeida <daniel.almeida@collabora.com>]

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.

Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/helpers.c          |   1 +
 rust/helpers/irq.c              |   9 ++
 rust/kernel/irq.rs              |   5 +
 rust/kernel/irq/request.rs      | 267 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 283 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 7e8f2285064797d5bbac5583990ff823b76c6bdc..fc73b89ff9d539e536a5da9388e4926a91a6130e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -52,6 +52,7 @@
 #include <linux/ethtool.h>
 #include <linux/file.h>
 #include <linux/firmware.h>
+#include <linux/interrupt.h>
 #include <linux/fs.h>
 #include <linux/jiffies.h>
 #include <linux/jump_label.h>
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 0b09bd0e3561c7bf80bf79faf1aebd7eeb851984..653c3f7b85c5f7192b1584c748a9d7e4af3796e9 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -22,6 +22,7 @@
 #include "dma.c"
 #include "drm.c"
 #include "err.c"
+#include "irq.c"
 #include "fs.c"
 #include "io.c"
 #include "jump_label.c"
diff --git a/rust/helpers/irq.c b/rust/helpers/irq.c
new file mode 100644
index 0000000000000000000000000000000000000000..1faca428e2c047a656dec3171855c1508d67e60b
--- /dev/null
+++ b/rust/helpers/irq.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/interrupt.h>
+
+int rust_helper_request_irq(unsigned int irq, irq_handler_t handler,
+			    unsigned long flags, const char *name, void *dev)
+{
+	return request_irq(irq, handler, flags, name, dev);
+}
diff --git a/rust/kernel/irq.rs b/rust/kernel/irq.rs
index 9abd9a6dc36f3e3ecc1f92ad7b0040176b56a079..01bd08884b72c2a3a9460897bce751c732a19794 100644
--- a/rust/kernel/irq.rs
+++ b/rust/kernel/irq.rs
@@ -12,3 +12,8 @@
 
 /// Flags to be used when registering IRQ handlers.
 pub mod flags;
+
+/// IRQ allocation and handling.
+pub mod request;
+
+pub use request::{Handler, IrqRequest, IrqReturn, Registration};
diff --git a/rust/kernel/irq/request.rs b/rust/kernel/irq/request.rs
new file mode 100644
index 0000000000000000000000000000000000000000..2f4637d8bc4c9fda23cbc8307687035957b0042a
--- /dev/null
+++ b/rust/kernel/irq/request.rs
@@ -0,0 +1,267 @@
+// 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;
+use crate::device::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 an IrqHandler or a ThreadedIrqHandler.
+#[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`.
+    pub(crate) unsafe fn new(dev: &'a Device<Bound>, irq: u32) -> Self {
+        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
+/// [`AtomicU32`](core::sync::AtomicU32) to provide the interior mutability.
+///
+/// ```
+/// use core::sync::atomic::AtomicU32;
+/// use core::sync::atomic::Ordering;
+///
+/// use kernel::prelude::*;
+/// use kernel::device::Bound;
+/// use kernel::irq::flags;
+/// use kernel::irq::Registration;
+/// use kernel::irq::IrqRequest;
+/// use kernel::irq::IrqReturn;
+/// use kernel::sync::Arc;
+/// use kernel::c_str;
+/// use kernel::alloc::flags::GFP_KERNEL;
+///
+/// // Declare a struct that will be passed in when the interrupt fires. The u32
+/// // merely serves as an example of some internal data.
+/// struct Data(AtomicU32);
+///
+/// // [`kernel::irq::request::Handler::handle`] takes `&self`. This example
+/// // illustrates how interior mutability can be used when sharing the data
+/// // between process context and IRQ context.
+///
+/// type Handler = Data;
+///
+/// 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 {
+///         self.0.fetch_add(1, Ordering::Relaxed);
+///
+///         IrqReturn::Handled
+///     }
+/// }
+///
+/// // Registers an IRQ handler for the given IrqRequest.
+/// //
+/// // This is executing in process context and assumes that `request` was
+/// // previously acquired from a device.
+/// fn register_irq(handler: Handler, request: IrqRequest<'_>) -> Result<Arc<Registration<Handler>>> {
+///     let registration = Registration::new(request, flags::SHARED, c_str!("my_device"), handler);
+///
+///     let registration = Arc::pin_init(registration, GFP_KERNEL)?;
+///
+///     // The data can be accessed from process context too.
+///     registration.handler().0.fetch_add(1, Ordering::Relaxed);
+///
+///     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: T,
+    ) -> impl PinInit<Self, Error> + 'a {
+        try_pin_init!(&this in Self {
+            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
+}

-- 
2.50.0