Re: [PATCH v7 1/1] rust: pci: add extended capability and SR-IOV support

On Tue Aug 4, 2026 at 6:16 PM CEST, Zhi Wang wrote:
> +/// Number of VF BAR register slots in an SR-IOV capability.
> +// CAST: `PCI_SRIOV_NUM_BARS` is 6, which fits in `usize`.

I think the more relevant point is that it is a constant coming from the PCIe
spec. (Plus, more SR-IOV BARs than addressable bytes wouldn't make a lot of
sense anyway. :)

> +const NUM_VF_BARS: usize = bindings::PCI_SRIOV_NUM_BARS as usize;
> +
> +/// PCI extended capability IDs.
> +#[repr(u16)]
> +#[derive(Debug, Clone, Copy, PartialEq, Eq)]
> +pub enum ExtCapId {
> +    /// Single Root I/O Virtualization.
> +    // CAST: `PCI_EXT_CAP_ID_SRIOV` is `0x10`, which fits in `u16`.

Same here, I'd mention that it is a constant from the spec.

> +    Sriov = bindings::PCI_EXT_CAP_ID_SRIOV as u16,
> +}

[...]

> +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.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```no_run
> +    /// use kernel::pci;
> +    ///
> +    /// fn probe_sriov(
> +    ///     pdev: &pci::Device<kernel::device::Bound>,
> +    /// ) -> Result<(), kernel::error::Error> {

Just Result; please also import kernel::device::Bound for readability.

io_read!() should be imported from kernel::io::.

> +/// SR-IOV register layout per PCIe spec (64 bytes starting at cap offset).
> +#[repr(C)]
> +#[derive(FromBytes, IntoBytes)]
> +pub struct ExtSriovRegs {
> +    /// Extended capability header.
> +    pub header: u32,
> +    /// SR-IOV capabilities.
> +    pub cap: u32,
> +    /// SR-IOV control.
> +    pub ctrl: u16,
> +    /// SR-IOV status.
> +    pub status: u16,

This is not a raw value, but a bitfield and should be represented as such (might
be true for some other fields as well).

I think for this to work it needs Gary's recent I/O series though; I can merge
both together next cycle and share with drm-rust.

> +    /// 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,
> +}