[PATCH v3] rust: pci: Allocate and manage PCI interrupt vectors

[Joel Fernandes <joelagnelf@nvidia.com>]

Add support to PCI rust module to allocate, free and manage IRQ vectors.
Integrate with devres for managing the allocated resources.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
v2->v3:
  Various changes suggested by Danilo and Bjorn (mostly comment changes and
  changing the registration order of the code).
  Link: https://lore.kernel.org/all/20251002183912.1096508-1-joelagnelf@nvidia.com/

 rust/kernel/pci.rs | 208 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 195 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 78271bf88cea..8c465d081015 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -6,8 +6,9 @@
 
 use crate::{
     bindings, container_of, device,
+    device::Bound,
     device_id::{RawDeviceId, RawDeviceIdIndex},
-    devres::Devres,
+    devres::{self, Devres},
     driver,
     error::{from_result, to_result, Result},
     io::{Io, IoRaw},
@@ -19,7 +20,7 @@
 };
 use core::{
     marker::PhantomData,
-    ops::Deref,
+    ops::{Deref, RangeInclusive},
     ptr::{addr_of_mut, NonNull},
 };
 use kernel::prelude::*;
@@ -28,6 +29,58 @@
 
 pub use self::id::{Class, ClassMask, Vendor};
 
+/// IRQ type flags for PCI interrupt allocation.
+#[derive(Debug, Clone, Copy)]
+pub enum IrqType {
+    /// INTx interrupts.
+    Intx,
+    /// Message Signaled Interrupts (MSI).
+    Msi,
+    /// Extended Message Signaled Interrupts (MSI-X).
+    MsiX,
+}
+
+impl IrqType {
+    /// Convert to the corresponding kernel flags.
+    const fn as_raw(self) -> u32 {
+        match self {
+            IrqType::Intx => bindings::PCI_IRQ_INTX,
+            IrqType::Msi => bindings::PCI_IRQ_MSI,
+            IrqType::MsiX => bindings::PCI_IRQ_MSIX,
+        }
+    }
+}
+
+/// Set of IRQ types that can be used for PCI interrupt allocation.
+#[derive(Debug, Clone, Copy, Default)]
+pub struct IrqTypes(u32);
+
+impl IrqTypes {
+    /// Create a set containing all IRQ types (MSI-X, MSI, and Legacy).
+    pub const fn all() -> Self {
+        Self(bindings::PCI_IRQ_ALL_TYPES)
+    }
+
+    /// Build a set of IRQ types.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// // Create a set with only MSI and MSI-X (no legacy interrupts).
+    /// let msi_only = IrqTypes::default()
+    ///     .with(IrqType::Msi)
+    ///     .with(IrqType::MsiX);
+    /// ```
+    pub const fn with(self, irq_type: IrqType) -> Self {
+        Self(self.0 | irq_type.as_raw())
+    }
+
+    /// Get the raw flags value.
+    const fn as_raw(self) -> u32 {
+        self.0
+    }
+}
+
 /// An adapter for the registration of PCI drivers.
 pub struct Adapter<T: Driver>(T);
 
@@ -516,6 +569,90 @@ pub fn pci_class(&self) -> Class {
     }
 }
 
+/// Represents an allocated IRQ vector for a specific PCI device.
+///
+/// This type ties an IRQ vector to the device it was allocated for,
+/// ensuring the vector is only used with the correct device.
+#[derive(Clone, Copy)]
+pub struct IrqVector<'a> {
+    dev: &'a Device<Bound>,
+    index: u32,
+}
+
+impl<'a> IrqVector<'a> {
+    /// Creates a new `IrqVector` for the given device and index.
+    ///
+    /// # Safety
+    ///
+    /// `index` must be a valid IRQ vector index for `dev`.
+    /// `dev` must point to a `struct pci_dev` that has successfully allocated  IRQ vectors.
+    unsafe fn new(dev: &'a Device<Bound>, index: u32) -> Self {
+        Self { dev, index }
+    }
+
+    /// Returns the raw vector index.
+    fn index(&self) -> u32 {
+        self.index
+    }
+}
+
+/// Represents an IRQ vector allocation for a PCI device.
+///
+/// This type ensures that IRQ vectors are properly allocated and freed by
+/// tying the allocation to the lifetime of this registration object.
+///
+/// # Invariants
+///
+/// `dev` points to a `struct pci_dev` that has successfully allocated IRQ vectors.
+struct IrqVectorRegistration {
+    dev: ARef<Device>,
+}
+
+impl IrqVectorRegistration {
+    /// Allocate and register IRQ vectors for the given PCI device.
+    ///
+    /// Allocates IRQ vectors and registers them with devres for automatic cleanup.
+    /// Returns a range of valid IRQ vectors.
+    fn register<'a>(
+        dev: &'a Device<Bound>,
+        min_vecs: u32,
+        max_vecs: u32,
+        irq_types: IrqTypes,
+    ) -> Result<RangeInclusive<IrqVector<'a>>> {
+        // SAFETY:
+        // - `dev.as_raw()` is guaranteed to be a valid pointer to a `struct pci_dev`
+        //   by the type invariant of `Device`.
+        // - `pci_alloc_irq_vectors` internally validates all other parameters
+        //   and returns error codes.
+        let ret = unsafe {
+            bindings::pci_alloc_irq_vectors(dev.as_raw(), min_vecs, max_vecs, irq_types.as_raw())
+        };
+
+        to_result(ret)?;
+        let count = ret as u32;
+
+        // SAFETY:
+        // - `pci_alloc_irq_vectors` returns the number of allocated vectors on success.
+        // - Vectors are 0-based, so valid indices are [0, count-1].
+        // - `pci_alloc_irq_vectors` guarantees count >= min_vecs > 0, so both 0 and count - 1
+        //   are valid IRQ vector indices for device `dev`.
+        let range = unsafe { IrqVector::new(dev, 0)..=IrqVector::new(dev, count - 1) };
+
+        let irq_vecs = Self { dev: dev.into() };
+        devres::register(dev.as_ref(), irq_vecs, GFP_KERNEL)?;
+
+        Ok(range)
+    }
+}
+
+impl Drop for IrqVectorRegistration {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariant, `self.dev` is a valid `ARef` to a `struct pci_dev`
+        // that has successfully allocated IRQ vectors.
+        unsafe { bindings::pci_free_irq_vectors(self.dev.as_raw()) };
+    }
+}
+
 impl Device<device::Bound> {
     /// Mapps an entire PCI-BAR after performing a region-request on it. I/O operation bound checks
     /// can be performed on compile time for offsets (plus the requested type size) < SIZE.
@@ -536,10 +673,15 @@ pub fn iomap_region<'a>(
         self.iomap_region_sized::<0>(bar, name)
     }
 
-    /// Returns an [`IrqRequest`] for the IRQ vector at the given index, if any.
-    pub fn irq_vector(&self, index: u32) -> Result<IrqRequest<'_>> {
+    /// Returns an [`IrqRequest`] for the given IRQ vector.
+    pub fn irq_vector(&self, vector: IrqVector<'_>) -> Result<IrqRequest<'_>> {
+        // Verify that the vector belongs to this device
+        if !core::ptr::eq(vector.dev.as_raw(), self.as_raw()) {
+            return Err(EINVAL);
+        }
+
         // SAFETY: `self.as_raw` returns a valid pointer to a `struct pci_dev`.
-        let irq = unsafe { crate::bindings::pci_irq_vector(self.as_raw(), index) };
+        let irq = unsafe { crate::bindings::pci_irq_vector(self.as_raw(), vector.index()) };
         if irq < 0 {
             return Err(crate::error::Error::from_errno(irq));
         }
@@ -547,35 +689,75 @@ pub fn irq_vector(&self, index: u32) -> Result<IrqRequest<'_>> {
         Ok(unsafe { IrqRequest::new(self.as_ref(), irq as u32) })
     }
 
-    /// Returns a [`kernel::irq::Registration`] for the IRQ vector at the given
-    /// index.
+    /// Returns a [`kernel::irq::Registration`] for the given IRQ vector.
     pub fn request_irq<'a, T: crate::irq::Handler + 'static>(
         &'a self,
-        index: u32,
+        vector: IrqVector<'_>,
         flags: irq::Flags,
         name: &'static CStr,
         handler: impl PinInit<T, Error> + 'a,
     ) -> Result<impl PinInit<irq::Registration<T>, Error> + 'a> {
-        let request = self.irq_vector(index)?;
+        let request = self.irq_vector(vector)?;
 
         Ok(irq::Registration::<T>::new(request, flags, name, handler))
     }
 
-    /// Returns a [`kernel::irq::ThreadedRegistration`] for the IRQ vector at
-    /// the given index.
+    /// Returns a [`kernel::irq::ThreadedRegistration`] for the given IRQ vector.
     pub fn request_threaded_irq<'a, T: crate::irq::ThreadedHandler + 'static>(
         &'a self,
-        index: u32,
+        vector: IrqVector<'_>,
         flags: irq::Flags,
         name: &'static CStr,
         handler: impl PinInit<T, Error> + 'a,
     ) -> Result<impl PinInit<irq::ThreadedRegistration<T>, Error> + 'a> {
-        let request = self.irq_vector(index)?;
+        let request = self.irq_vector(vector)?;
 
         Ok(irq::ThreadedRegistration::<T>::new(
             request, flags, name, handler,
         ))
     }
+
+    /// Allocate IRQ vectors for this PCI device with automatic cleanup.
+    ///
+    /// Allocates between `min_vecs` and `max_vecs` interrupt vectors for the device.
+    /// The allocation will use MSI-X, MSI, or legacy interrupts based on the `irq_types`
+    /// parameter and hardware capabilities. When multiple types are specified, the kernel
+    /// will try them in order of preference: MSI-X first, then MSI, then legacy interrupts.
+    ///
+    /// The allocated vectors are automatically freed when the device is unbound, using the
+    /// devres (device resource management) system.
+    ///
+    /// # Arguments
+    ///
+    /// * `min_vecs` - Minimum number of vectors required.
+    /// * `max_vecs` - Maximum number of vectors to allocate.
+    /// * `irq_types` - Types of interrupts that can be used.
+    ///
+    /// # Returns
+    ///
+    /// Returns a range of IRQ vectors that were successfully allocated, or an error if the
+    /// allocation fails or cannot meet the minimum requirement.
+    ///
+    /// # Examples
+    ///
+    /// ```ignore
+    /// // Allocate using any available interrupt type in the order mentioned above.
+    /// let vectors = dev.alloc_irq_vectors(1, 32, IrqTypes::all())?;
+    ///
+    /// // Allocate MSI or MSI-X only (no legacy interrupts).
+    /// let msi_only = IrqTypes::default()
+    ///     .with(IrqType::Msi)
+    ///     .with(IrqType::MsiX);
+    /// let vectors = dev.alloc_irq_vectors(4, 16, msi_only)?;
+    /// ```
+    pub fn alloc_irq_vectors(
+        &self,
+        min_vecs: u32,
+        max_vecs: u32,
+        irq_types: IrqTypes,
+    ) -> Result<RangeInclusive<IrqVector<'_>>> {
+        IrqVectorRegistration::register(self, min_vecs, max_vecs, irq_types)
+    }
 }
 
 impl Device<device::Core> {
-- 
2.34.1