[PATCH v8 1/1] rust: pci: add extended capability and SR-IOV support

Rust PCI drivers have no typed interface for locating and accessing PCIe
extended capabilities.

The SR-IOV extended capability describes VF topology and VF BARs. Expose
this information through the Rust PCI abstraction so drivers can use the
existing typed configuration-space accessors instead of raw bindings.

Define ExtCapability to associate a capability ID with a register layout,
and add ConfigSpace::find_ext_capability() to locate and project that
layout. Bound the view at the next capability or the end of extended
configuration space. Add ExtSriovRegs and a decoded VF BAR iterator that
reads and validates all six VF BAR register slots up front, yields decoded
BAR addresses and widths in logical order, and keeps the raw
configuration-space slot advancement internal. Since PCI_EXT_CAP_NEXT() is
a function-like macro, expose it through a Rust helper.

Link: https://lore.kernel.org/rust-for-linux/[email protected]/
Cc: Alexandre Courbot <[email protected]>
Cc: Gary Guo <[email protected]>
Signed-off-by: Zhi Wang <[email protected]>
---
 rust/helpers/pci.c     |   5 +
 rust/kernel/pci.rs     |   8 +
 rust/kernel/pci/cap.rs | 329 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 342 insertions(+)
 create mode 100644 rust/kernel/pci/cap.rs

diff --git a/rust/helpers/pci.c b/rust/helpers/pci.c
index 4ebf256dff23..b946b14d79e4 100644
--- a/rust/helpers/pci.c
+++ b/rust/helpers/pci.c
@@ -24,6 +24,11 @@ __rust_helper bool rust_helper_dev_is_pci(const struct device *dev)
 	return dev_is_pci(dev);
 }
 
+__rust_helper u32 rust_helper_pci_ext_cap_next(u32 header)
+{
+	return PCI_EXT_CAP_NEXT(header);
+}
+
 #ifndef CONFIG_PCI_IOV
 __rust_helper unsigned int
 rust_helper_pci_sriov_get_totalvfs(struct pci_dev *pdev)
diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
index 9f19ccd5905c..008c2770a3f3 100644
--- a/rust/kernel/pci.rs
+++ b/rust/kernel/pci.rs
@@ -32,10 +32,18 @@
     },
 };
 
+mod cap;
 mod id;
 mod io;
 mod irq;
 
+pub use self::cap::{
+    ExtCapId,
+    ExtCapability,
+    ExtSriovCapability,
+    ExtSriovRegs,
+    ExtSriovVfBar, //
+};
 pub use self::id::{
     Class,
     ClassMask,
diff --git a/rust/kernel/pci/cap.rs b/rust/kernel/pci/cap.rs
new file mode 100644
index 000000000000..ddb3fd73e195
--- /dev/null
+++ b/rust/kernel/pci/cap.rs
@@ -0,0 +1,329 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! PCI extended capability support.
+
+use super::{
+    io::ConfigSpaceBackend,
+    ConfigSpace,
+    Extended, //
+};
+use crate::{
+    bindings,
+    io::{
+        Io,
+        IoBackend,
+        Region, //
+    },
+    num::Bounded,
+    prelude::*,
+};
+
+/// Number of VF BAR register slots in an SR-IOV capability.
+// CAST: `PCI_SRIOV_NUM_BARS` is the PCIe-specified number of VF BAR register slots and fits in
+// `usize`.
+const NUM_VF_BARS: usize = bindings::PCI_SRIOV_NUM_BARS as usize;
+
+/// PCI extended capability IDs.
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ExtCapId(u16);
+
+impl ExtCapId {
+    /// Single Root I/O Virtualization.
+    // CAST: PCI extended capability IDs are 16-bit values defined by the PCIe specification.
+    pub const SRIOV: Self = Self(bindings::PCI_EXT_CAP_ID_SRIOV as u16);
+
+    /// Creates an extended capability ID from its raw PCIe value.
+    #[inline]
+    pub const fn new(id: u16) -> Self {
+        Self(id)
+    }
+
+    /// Returns the raw PCIe extended capability ID.
+    #[inline]
+    const fn as_raw(self) -> u16 {
+        self.0
+    }
+}
+
+/// A typed PCI extended capability register layout.
+///
+/// Implementors describe the register layout of one extended capability. The layout must start at
+/// the extended capability header, and [`Self::ID`] must identify that layout.
+pub trait ExtCapability: FromBytes + IntoBytes {
+    /// PCI extended capability ID for this register layout.
+    const ID: ExtCapId;
+}
+
+impl<'a> ConfigSpace<'a, Extended> {
+    /// Finds and projects an extended capability into its typed register layout.
+    ///
+    /// Returns [`None`] if the device does not implement the capability.
+    ///
+    /// Returns an error if the capability is present but its register span is too small or
+    /// insufficiently aligned for `C`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use kernel::{
+    ///     device::Bound,
+    ///     io::io_read,
+    ///     pci,
+    ///     prelude::*,
+    /// };
+    ///
+    /// fn probe_sriov(pdev: &pci::Device<Bound>) -> Result {
+    ///     let Some(sriov) = pdev
+    ///         .config_space_extended()?
+    ///         .find_ext_capability::<pci::ExtSriovRegs>()?
+    ///     else {
+    ///         return Ok(());
+    ///     };
+    ///
+    ///     let total_vfs = io_read!(sriov, .total_vfs);
+    ///     let vf_offset = io_read!(sriov, .vf_offset);
+    ///     let mut vf_bars = sriov.vf_bars()?;
+    ///     let bar0 = vf_bars.next().ok_or(EINVAL)?;
+    ///     let bar1 = vf_bars.next().ok_or(EINVAL)?;
+    ///     let bar2 = vf_bars.next().ok_or(EINVAL)?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn find_ext_capability<C: ExtCapability>(&self) -> Result<Option<ConfigSpace<'a, C>>> {
+        let offset = usize::from(
+            // SAFETY: `self.pdev` is valid by the type invariant of `ConfigSpace`.
+            unsafe {
+                bindings::pci_find_ext_capability(self.pdev.as_raw(), i32::from(C::ID.as_raw()))
+            },
+        );
+
+        if offset == 0 {
+            return Ok(None);
+        }
+
+        let size = self.calculate_ext_cap_size(offset)?;
+
+        let base = ConfigSpaceBackend::as_ptr(*self)
+            .cast::<u8>()
+            .wrapping_add(offset);
+        let ptr = Region::<0>::ptr_try_from_raw_parts_mut(base, size)?;
+
+        // SAFETY: `offset` was returned by `pci_find_ext_capability`, and
+        // `calculate_ext_cap_size` bounds `ptr` at the next capability or the end of the extended
+        // configuration space. `ptr_try_from_raw_parts_mut` verified the region layout.
+        let capability = unsafe { ConfigSpaceBackend::project_view(*self, ptr) };
+
+        capability.try_cast::<C>().map(Some)
+    }
+
+    /// Calculates the size of the extended capability at `offset`.
+    ///
+    /// The capability extends to the next extended capability, or to the end of the extended
+    /// configuration space if it is the last one. `offset` must be a DWORD-aligned offset within
+    /// the extended configuration space returned by `pci_find_ext_capability`. Returns an error if
+    /// the capability header is outside the extended configuration space.
+    fn calculate_ext_cap_size(&self, offset: usize) -> Result<usize> {
+        let header = self.try_read32(offset)?;
+        // SAFETY: Pure bit manipulation, no preconditions.
+        // CAST: The next-cap pointer is a 12-bit field (max 0xFFC), always fits in `usize`.
+        let next = unsafe { bindings::pci_ext_cap_next(header) } as usize;
+
+        Ok(if next > offset {
+            next - offset
+        } else {
+            self.size() - offset
+        })
+    }
+}
+
+/// SR-IOV register layout per PCIe spec (64 bytes starting at cap offset).
+#[repr(C)]
+#[derive(FromBytes, IntoBytes)]
+pub struct ExtSriovRegs {
+    /// Extended capability header.
+    _header: u32,
+    /// SR-IOV capabilities.
+    pub cap: u32,
+    /// SR-IOV control.
+    pub ctrl: u16,
+    /// SR-IOV status.
+    pub status: u16,
+    /// Initial VFs.
+    pub initial_vfs: u16,
+    /// Total VFs.
+    pub total_vfs: u16,
+    /// Number of VFs.
+    pub num_vfs: u16,
+    /// Function dependency link.
+    pub func_dep_link: u8,
+    _reserved_0: u8,
+    /// First VF offset.
+    pub vf_offset: u16,
+    /// VF stride.
+    pub vf_stride: u16,
+    _reserved_1: u16,
+    /// VF device ID.
+    pub vf_device_id: u16,
+    /// Supported page sizes.
+    pub supported_page_sizes: u32,
+    /// System page size.
+    pub system_page_size: u32,
+    /// VF BARs (BAR0–BAR5).
+    pub vf_bar: [u32; NUM_VF_BARS],
+    /// VF migration state array offset.
+    pub migration_state: u32,
+}
+
+impl ExtCapability for ExtSriovRegs {
+    const ID: ExtCapId = ExtCapId::SRIOV;
+}
+
+/// A typed view of an SR-IOV extended capability.
+pub type ExtSriovCapability<'a> = ConfigSpace<'a, ExtSriovRegs>;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum VfBarMemoryType {
+    Bits32,
+    Bits64,
+}
+
+impl TryFrom<Bounded<u32, 2>> for VfBarMemoryType {
+    type Error = Error;
+
+    fn try_from(value: Bounded<u32, 2>) -> Result<Self> {
+        match value.get() {
+            0b00 => Ok(Self::Bits32),
+            0b10 => Ok(Self::Bits64),
+            _ => Err(EINVAL),
+        }
+    }
+}
+
+impl From<VfBarMemoryType> for Bounded<u32, 2> {
+    fn from(value: VfBarMemoryType) -> Self {
+        match value {
+            VfBarMemoryType::Bits32 => Self::new::<0b00>(),
+            VfBarMemoryType::Bits64 => Self::new::<0b10>(),
+        }
+    }
+}
+
+crate::bitfield! {
+    /// Low DWORD of an SR-IOV VF BAR.
+    struct VfBarLow(u32) {
+        /// Base address bits 31:4.
+        31:4 address;
+        /// Whether the address range is prefetchable.
+        3:3 prefetchable => bool;
+        /// Memory BAR type.
+        2:1 memory_type ?=> VfBarMemoryType;
+        /// Whether this is an I/O-space BAR.
+        0:0 io_space => bool;
+    }
+}
+
+/// A decoded VF BAR register encoding.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ExtSriovVfBar {
+    /// The BAR address without PCI attribute bits.
+    pub address: u64,
+
+    /// Whether the BAR is 64-bit.
+    pub is_64bit: bool,
+}
+
+/// Iterator over decoded VF BAR register encodings.
+///
+/// A 32-bit memory BAR encoding uses one register. A 64-bit memory BAR encoding uses that register
+/// for bits 31:0 and the immediately following register for bits 63:32.
+///
+/// # Invariants
+///
+/// - `next_bar <= bar_count <= NUM_VF_BARS`.
+/// - Entries before `bar_count` contain decoded VF BARs in logical order.
+struct ExtSriovVfBars {
+    bars: [ExtSriovVfBar; NUM_VF_BARS],
+    bar_count: usize,
+    next_bar: usize,
+}
+
+impl ExtSriovVfBars {
+    fn new(slots: [u32; NUM_VF_BARS]) -> Result<Self> {
+        let mut bars = [ExtSriovVfBar {
+            address: 0,
+            is_64bit: false,
+        }; NUM_VF_BARS];
+        let mut bar_count = 0;
+        let mut config_slot = 0;
+
+        while config_slot < NUM_VF_BARS {
+            let low = VfBarLow::from(slots[config_slot]);
+
+            if low.io_space() {
+                return Err(EINVAL);
+            }
+
+            let is_64bit = low.memory_type()? == VfBarMemoryType::Bits64;
+            let low_address = u64::from(low.address()) << VfBarLow::ADDRESS_SHIFT;
+
+            let address = if is_64bit {
+                if config_slot + 1 >= NUM_VF_BARS {
+                    return Err(EINVAL);
+                }
+
+                let high = slots[config_slot + 1];
+                config_slot += 2;
+                (u64::from(high) << 32) | low_address
+            } else {
+                config_slot += 1;
+                low_address
+            };
+
+            bars[bar_count] = ExtSriovVfBar { address, is_64bit };
+            bar_count += 1;
+        }
+
+        Ok(Self {
+            bars,
+            bar_count,
+            next_bar: 0,
+        })
+    }
+}
+
+impl Iterator for ExtSriovVfBars {
+    type Item = ExtSriovVfBar;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.next_bar >= self.bar_count {
+            return None;
+        }
+
+        let bar = self.bars[self.next_bar];
+        self.next_bar += 1;
+        Some(bar)
+    }
+}
+
+impl ExtSriovCapability<'_> {
+    /// Returns an iterator over decoded VF BAR register encodings.
+    ///
+    /// All six raw VF BAR register slots are read and decoded up front. A 32-bit encoding yields
+    /// one entry; a 64-bit encoding combines two slots into one entry.
+    ///
+    /// A zero-valued low DWORD is yielded as a 32-bit BAR at address zero; this method does not
+    /// probe whether a BAR is implemented.
+    ///
+    /// Returns [`EINVAL`] and logs an error if a BAR low DWORD does not encode a 32-bit or 64-bit
+    /// memory BAR, or if a 64-bit encoding has no upper DWORD.
+    pub fn vf_bars(&self) -> Result<impl Iterator<Item = ExtSriovVfBar>> {
+        let slots: [u32; NUM_VF_BARS] =
+            core::array::from_fn(|slot| crate::io_read!(*self, .vf_bar[panic: slot]));
+
+        ExtSriovVfBars::new(slots).inspect_err(|_| {
+            dev_err!(self.pdev, "invalid VF BAR encoding in SR-IOV capability\n");
+        })
+    }
+}
-- 
2.53.0