rust: irq: add flags module

Manipulating IRQ flags (i.e.: IRQF_*) will soon be necessary, specially to
register IRQ handlers through bindings::request_irq().

Add a kernel::irq::Flags for that purpose.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250811-topics-tyr-request_irq2-v9-2-0485dcd9bcbf@collabora.com
[ Use expect(dead_code) for into_inner(), fix broken intra-doc link and
  typo. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/irq.rs

@@ -9,3 +9,8 @@
 //! drivers to register a handler for a given IRQ line.
 //!
 //! C header: [`include/linux/device.h`](srctree/include/linux/interrupt.h)
+
+/// Flags to be used when registering IRQ handlers.
+mod flags;
+
+pub use flags::Flags;

rust/kernel/irq/flags.rs

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+// SPDX-FileCopyrightText: Copyright 2025 Collabora ltd.
+
+use crate::bindings;
+use crate::prelude::*;
+
+/// Flags to be used when registering IRQ handlers.
+///
+/// Flags can be used to request specific behaviors when registering an IRQ
+/// handler, and can be combined using the `|`, `&`, and `!` operators to
+/// further control the system's behavior.
+///
+/// A common use case is to register a shared interrupt, as sharing the line
+/// between devices is increasingly common in modern systems and is even
+/// required for some buses. This requires setting [`Flags::SHARED`] when
+/// requesting the interrupt. Other use cases include setting the trigger type
+/// through `Flags::TRIGGER_*`, which determines when the interrupt fires, or
+/// controlling whether the interrupt is masked after the handler runs by using
+/// [`Flags::ONESHOT`].
+///
+/// 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
+/// [`Flags::SHARED`] and on the same trigger type, if set.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Flags(c_ulong);
+
+impl Flags {
+    /// Use the interrupt line as already configured.
+    pub const TRIGGER_NONE: Flags = Flags::new(bindings::IRQF_TRIGGER_NONE);
+
+    /// The interrupt is triggered when the signal goes from low to high.
+    pub const TRIGGER_RISING: Flags = Flags::new(bindings::IRQF_TRIGGER_RISING);
+
+    /// The interrupt is triggered when the signal goes from high to low.
+    pub const TRIGGER_FALLING: Flags = Flags::new(bindings::IRQF_TRIGGER_FALLING);
+
+    /// The interrupt is triggered while the signal is held high.
+    pub const TRIGGER_HIGH: Flags = Flags::new(bindings::IRQF_TRIGGER_HIGH);
+
+    /// The interrupt is triggered while the signal is held low.
+    pub const TRIGGER_LOW: Flags = Flags::new(bindings::IRQF_TRIGGER_LOW);
+
+    /// Allow sharing the IRQ among several devices.
+    pub const SHARED: Flags = Flags::new(bindings::IRQF_SHARED);
+
+    /// Set by callers when they expect sharing mismatches to occur.
+    pub const PROBE_SHARED: Flags = Flags::new(bindings::IRQF_PROBE_SHARED);
+
+    /// Flag to mark this interrupt as timer interrupt.
+    pub const TIMER: Flags = Flags::new(bindings::IRQF_TIMER);
+
+    /// Interrupt is per CPU.
+    pub const PERCPU: Flags = Flags::new(bindings::IRQF_PERCPU);
+
+    /// Flag to exclude this interrupt from irq balancing.
+    pub const NOBALANCING: Flags = Flags::new(bindings::IRQF_NOBALANCING);
+
+    /// Interrupt is used for polling (only the interrupt that is registered
+    /// first in a shared interrupt is considered for performance reasons).
+    pub const IRQPOLL: Flags = Flags::new(bindings::IRQF_IRQPOLL);
+
+    /// Interrupt is not re-enabled after the hardirq handler finished. Used by
+    /// threaded interrupts which need to keep the irq line disabled until the
+    /// threaded handler has been run.
+    pub const ONESHOT: Flags = Flags::new(bindings::IRQF_ONESHOT);
+
+    /// Do not disable this IRQ during suspend. Does not guarantee that this
+    /// interrupt will wake the system from a suspended state.
+    pub const NO_SUSPEND: Flags = Flags::new(bindings::IRQF_NO_SUSPEND);
+
+    /// Force enable it on resume even if [`Flags::NO_SUSPEND`] is set.
+    pub const FORCE_RESUME: Flags = Flags::new(bindings::IRQF_FORCE_RESUME);
+
+    /// Interrupt cannot be threaded.
+    pub const NO_THREAD: Flags = Flags::new(bindings::IRQF_NO_THREAD);
+
+    /// Resume IRQ early during syscore instead of at device resume time.
+    pub const EARLY_RESUME: Flags = Flags::new(bindings::IRQF_EARLY_RESUME);
+
+    /// If the IRQ is shared with a [`Flags::NO_SUSPEND`] user, execute this
+    /// interrupt handler after suspending interrupts. For system wakeup devices
+    /// users need to implement wakeup detection in their interrupt handlers.
+    pub const COND_SUSPEND: Flags = Flags::new(bindings::IRQF_COND_SUSPEND);
+
+    /// Don't enable IRQ or NMI automatically when users request it. Users will
+    /// enable it explicitly by `enable_irq` or `enable_nmi` later.
+    pub const NO_AUTOEN: Flags = Flags::new(bindings::IRQF_NO_AUTOEN);
+
+    /// Exclude from runnaway detection for IPI and similar handlers, depends on
+    /// `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
+    }
+
+    const fn new(value: u32) -> Self {
+        build_assert!(value as u64 <= c_ulong::MAX as u64);
+        Self(value as c_ulong)
+    }
+}
+
+impl core::ops::BitOr for Flags {
+    type Output = Self;
+    fn bitor(self, rhs: Self) -> Self::Output {
+        Self(self.0 | rhs.0)
+    }
+}
+
+impl core::ops::BitAnd for Flags {
+    type Output = Self;
+    fn bitand(self, rhs: Self) -> Self::Output {
+        Self(self.0 & rhs.0)
+    }
+}
+
+impl core::ops::Not for Flags {
+    type Output = Self;
+    fn not(self) -> Self::Output {
+        Self(!self.0)
+    }
+}