Re: [PATCH v13 2/3] rust: io: mem: add a generic iomem abstraction

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Jul 11, 2025 at 07:32:28PM -0300, Daniel Almeida wrote:
> Add a generic iomem abstraction to safely read and write ioremapped
> regions. This abstraction requires a previously acquired IoRequest
> instance. This makes it so that both the resource and the device match,
> or, in other words, that the resource is indeed a valid resource for a
> given bound device.
> 
> A subsequent patch will add the ability to retrieve IoRequest instances
> from platform devices.
> 
> The reads and writes are done through IoRaw, and are thus checked either
> at compile-time, if the size of the region is known at that point, or at
> runtime otherwise.
> 
> Non-exclusive access to the underlying memory region is made possible to
> cater to cases where overlapped regions are unavoidable.
> 
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

> +impl<const SIZE: usize> IoMem<SIZE> {
> +    fn ioremap(resource: &Resource) -> Result<Self> {
> +        let size = resource.size();
> +        if size == 0 {
> +            return Err(EINVAL);
> +        }
> +
> +        let res_start = resource.start();
> +
> +        let addr = if resource
> +            .flags()
> +            .contains(io::resource::Flags::IORESOURCE_MEM_NONPOSTED)
> +        {
> +            // SAFETY:
> +            // - `res_start` and `size` are read from a presumably valid `struct resource`.
> +            // - `size` is known not to be zero at this point.
> +            unsafe { bindings::ioremap_np(res_start, size.try_into()?) }
> +        } else {
> +            // SAFETY:
> +            // - `res_start` and `size` are read from a presumably valid `struct resource`.
> +            // - `size` is known not to be zero at this point.
> +            unsafe { bindings::ioremap(res_start, size.try_into()?) }

I thought a bit more about this, and I think it's fine for these sizes to
be converted with try_into()?.

> +        };
> +
> +        if addr.is_null() {
> +            return Err(ENOMEM);
> +        }
> +
> +        let io = IoRaw::new(addr as usize, size.try_into()?)?;

Though may we could avoid converting it twice?

Alice