1 files changed, 115 insertions, 0 deletions
diff --git a/rust/hw/core/src/irq.rs b/rust/hw/core/src/irq.rs
new file mode 100644
index 0000000000..fead2bbe8e
--- /dev/null
+++ b/rust/hw/core/src/irq.rs
@@ -0,0 +1,115 @@
+// Copyright 2024 Red Hat, Inc.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings for interrupt sources
+
+use std::{
+    ffi::{c_int, CStr},
+    marker::PhantomData,
+    ptr,
+};
+
+use bql::BqlCell;
+use common::Opaque;
+use qom::{prelude::*, ObjectClass};
+
+use crate::bindings::{self, qemu_set_irq};
+
+/// An opaque wrapper around [`bindings::IRQState`].
+#[repr(transparent)]
+#[derive(Debug, qemu_api_macros::Wrapper)]
+pub struct IRQState(Opaque<bindings::IRQState>);
+
+/// Interrupt sources are used by devices to pass changes to a value (typically
+/// a boolean).  The interrupt sink is usually an interrupt controller or
+/// GPIO controller.
+///
+/// As far as devices are concerned, interrupt sources are always active-high:
+/// for example, `InterruptSource<bool>`'s [`raise`](InterruptSource::raise)
+/// method sends a `true` value to the sink.  If the guest has to see a
+/// different polarity, that change is performed by the board between the
+/// device and the interrupt controller.
+///
+/// Interrupts are implemented as a pointer to the interrupt "sink", which has
+/// type [`IRQState`].  A device exposes its source as a QOM link property using
+/// a function such as [`crate::sysbus::SysBusDeviceMethods::init_irq`], and
+/// initially leaves the pointer to a NULL value, representing an unconnected
+/// interrupt. To connect it, whoever creates the device fills the pointer with
+/// the sink's `IRQState *`, for example using `sysbus_connect_irq`.  Because
+/// devices are generally shared objects, interrupt sources are an example of
+/// the interior mutability pattern.
+///
+/// Interrupt sources can only be triggered under the Big QEMU Lock; `BqlCell`
+/// allows access from whatever thread has it.
+#[derive(Debug)]
+#[repr(transparent)]
+pub struct InterruptSource<T = bool>
+where
+    c_int: From<T>,
+{
+    cell: BqlCell<*mut bindings::IRQState>,
+    _marker: PhantomData<T>,
+}
+
+// SAFETY: the implementation asserts via `BqlCell` that the BQL is taken
+unsafe impl<T> Sync for InterruptSource<T> where c_int: From<T> {}
+
+impl InterruptSource<bool> {
+    /// Send a low (`false`) value to the interrupt sink.
+    pub fn lower(&self) {
+        self.set(false);
+    }
+
+    /// Send a high-low pulse to the interrupt sink.
+    pub fn pulse(&self) {
+        self.set(true);
+        self.set(false);
+    }
+
+    /// Send a high (`true`) value to the interrupt sink.
+    pub fn raise(&self) {
+        self.set(true);
+    }
+}
+
+impl<T> InterruptSource<T>
+where
+    c_int: From<T>,
+{
+    /// Send `level` to the interrupt sink.
+    pub fn set(&self, level: T) {
+        let ptr = self.cell.get();
+        // SAFETY: the pointer is retrieved under the BQL and remains valid
+        // until the BQL is released, which is after qemu_set_irq() is entered.
+        unsafe {
+            qemu_set_irq(ptr, level.into());
+        }
+    }
+
+    pub(crate) const fn as_ptr(&self) -> *mut *mut bindings::IRQState {
+        self.cell.as_ptr()
+    }
+
+    pub(crate) const fn slice_as_ptr(slice: &[Self]) -> *mut *mut bindings::IRQState {
+        assert!(!slice.is_empty());
+        slice[0].as_ptr()
+    }
+}
+
+impl Default for InterruptSource {
+    fn default() -> Self {
+        InterruptSource {
+            cell: BqlCell::new(ptr::null_mut()),
+            _marker: PhantomData,
+        }
+    }
+}
+
+unsafe impl ObjectType for IRQState {
+    type Class = ObjectClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_IRQ) };
+}
+
+qom_isa!(IRQState: Object);