Re: [PATCH v4 08/20] rust: pci: io: make `ConfigSpace` a view

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri Jun 12, 2026 at 1:28 AM JST, Gary Guo wrote:
> In order to support I/O projection, we are splitting I/O types into two
> categories: owned objects and views. Owned objects have a specific type
> that is related to setting up and tearing down, while views can have their
> type changed with I/O projection.
>
> Things like `IoMem` or `Bar` are owned objects, which requires setting up
> mapping and cleaning up on drop. On the other side, `ConfigSpace` is really
> just a view, as the resource is associated with the `pci::Device`.
>
> Remove the `ConfigSpaceKind` bound on `ConfigSpace` and make it a generic
> view. This means that `ConfigSpace` object now represents a subregion and
> therefore encodes offset (as address of pointers) and size (as metadata of
> pointers) itself. The full region case is still supported with offset 0 and
> size of `cfg_size`.
>
> Signed-off-by: Gary Guo <gary@garyguo.net>
> ---
>  rust/kernel/pci/io.rs | 64 +++++++++++++++++++++++++++++----------------------
>  1 file changed, 36 insertions(+), 28 deletions(-)
>
> diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> index e0acb62f58a2..89f4bb483a7f 100644
> --- a/rust/kernel/pci/io.rs
> +++ b/rust/kernel/pci/io.rs
> @@ -18,7 +18,6 @@
>      ptr::KnownSize, //
>  };
>  use core::{
> -    marker::PhantomData,
>      ops::Deref, //
>  };
>  
> @@ -53,33 +52,42 @@ pub const fn into_raw(self) -> usize {
>  /// Alias for extended (4096-byte) PCIe configuration space.
>  pub type Extended = Region<4096>;
>  
> -/// Trait for PCI configuration space size markers.
> -///
> -/// This trait is implemented by [`Normal`] and [`Extended`] to provide
> -/// compile-time knowledge of the configuration space size.
> -pub trait ConfigSpaceKind: KnownSize {}
> -
> -impl ConfigSpaceKind for Normal {}
> -
> -impl ConfigSpaceKind for Extended {}
> -
> -/// The PCI configuration space of a device.
> +/// A view of PCI configuration space of a device.
>  ///
>  /// Provides typed read and write accessors for configuration registers
>  /// using the standard `pci_read_config_*` and `pci_write_config_*` helpers.
>  ///
> -/// The generic parameter `S` indicates the maximum size of the configuration space.
> -/// Use [`Normal`] for 256-byte legacy configuration space or [`Extended`] for
> -/// 4096-byte PCIe extended configuration space (default).
> -pub struct ConfigSpace<'a, S: ?Sized + ConfigSpaceKind = Extended> {
> +/// The generic parameter `T` is the type of the view. The full configuration space is also a
> +/// special type of view; in such cases, `T` can be [`Normal`] for 256-byte legacy configuration
> +/// space or [`Extended`] for 4096-byte PCIe extended configuration space (default).
> +///
> +/// # Invariants
> +///
> +/// `ptr` is aligned and range `ptr..ptr + KnownSize::size(ptr)` is within
> +/// `0..pdev.cfg_size().into_raw()`.
> +pub struct ConfigSpace<'a, T: ?Sized = Extended> {
>      pub(crate) pdev: &'a Device<device::Bound>,
> -    _marker: PhantomData<S>,
> +    ptr: *mut T,

`ptr` is used as a pseudo-pointer here, can its documentation be more
explicit about that?

Regardless,

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>