Re: [PATCH v13 1/3] rust: io: add resource abstraction

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Jul 11, 2025 at 07:32:27PM -0300, Daniel Almeida wrote:
> In preparation for ioremap support, add a Rust abstraction for struct
> resource.
> 
> A future commit will introduce the Rust API to ioremap a resource from a
> platform device. The current abstraction, therefore, adds only the
> minimum API needed to get that done.
> 
> Co-developed-by: Fiona Behrens <me@kloenk.dev>
> Signed-off-by: Fiona Behrens <me@kloenk.dev>
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>

Some nits below, but overall LGTM. With those fixed:
Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> +    /// Requests a resource region.
> +    ///
> +    /// Exclusive access will be given and the region will be marked as busy.
> +    /// Further calls to [`Self::request_region`] will return [`None`] if
> +    /// the region, or a part of it, is already in use.
> +    pub fn request_region(
> +        &self,
> +        start: ResourceSize,
> +        size: ResourceSize,
> +        name: &'static CStr,
> +        flags: Flags,
> +    ) -> Option<Region> {
> +        // SAFETY:
> +        // - Safe as per the invariant of `Resource`.
> +        // - `__request_region` will store a reference to the name, but that is
> +        // safe as the name is 'static.
> +        let region = unsafe {
> +            bindings::__request_region(
> +                self.0.get(),
> +                start,
> +                size,
> +                name.as_char_ptr(),
> +                flags.0 as c_int,
> +            )
> +        };
> +
> +        Some(Region(NonNull::new(region)?))
> +    }
> +
> +    /// Returns the size of the resource.
> +    pub fn size(&self) -> ResourceSize {
> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`.
> +        unsafe { bindings::resource_size(inner) }
> +    }
> +
> +    /// Returns the start address of the resource.
> +    pub fn start(&self) -> u64 {

This should be a ResourceSize, right? You use the ResourceSize type for
the `start` when calling `request_region`.

Or ... should we have another PhysAddr typedef that we can use here?

> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`.
> +        unsafe { (*inner).start }
> +    }
> +
> +    /// Returns the name of the resource.
> +    pub fn name(&self) -> &'static CStr {
> +        let inner = self.0.get();
> +        // SAFETY: safe as per the invariants of `Resource`
> +        unsafe { CStr::from_char_ptr((*inner).name) }

This is 'static? I would like this safety comment to explicitly say that
the string always lives forever no matter what resource you call this
on.

Alice