Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and handlers

[Alice Ryhl <aliceryhl@google.com>]

On Thu, Jul 03, 2025 at 04:30:01PM -0300, Daniel Almeida wrote:
> 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      | 273 ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 289 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 8cbb660e2ec218021d16e6e0144acf6f4d7cca13..da0bd23fad59a2373bd873d12ad69c55208aaa38 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -51,6 +51,7 @@
>  #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 393ad201befb80a9ae39866a725744ab88620fbb..e3579fc7e1cfc30c913207a4a78b790259d7ae7a 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..4f4beaa3c7887660440b9ddc52414020a0d165ac
> --- /dev/null
> +++ b/rust/kernel/irq/request.rs
> @@ -0,0 +1,273 @@
> +// 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.
> +pub enum IrqReturn {
> +    /// The interrupt was not from this device or was not handled.
> +    None,
> +
> +    /// The interrupt was handled by this device.
> +    Handled,
> +}
> +
> +impl IrqReturn {
> +    fn into_inner(self) -> u32 {
> +        match self {
> +            IrqReturn::None => bindings::irqreturn_IRQ_NONE,
> +            IrqReturn::Handled => bindings::irqreturn_IRQ_HANDLED,

One option is to specify these in the enum:

/// The value that can be returned from an IrqHandler or a ThreadedIrqHandler.
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,
}

impl IrqReturn {
    fn into_inner(self) -> c_uint {
        self as c_uint
    }
}

> +
> +/// 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`.

I recall there being a clippy lint about the indentation here. Did it
not trigger?

/// - `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 kernel::ffi::c_void,

The c_void type is in the prelude.

> +}
> +
> +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 }
> +    }
> +}
> +
> +/// 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() as usize,
> +                                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 core::ffi::c_void,
> +) -> core::ffi::c_uint {

You should just use `c_uint` without the prefix. This way you get it
from `kernel::prelude::*` which has the correct typedefs rather than
`core::ffi`.

> +    // SAFETY: `ptr` is a pointer to T set in `Registration::new`
> +    let handler = unsafe { &*(ptr as *const T) };
> +    T::handle(handler).into_inner()
> +}
> 
> -- 
> 2.50.0
>