linux-kernel - Re: [PATCH] rust: platform: add Io support

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Message-ID: <CAH5fLghzPr8KgneqX=K=AfMYy2Neej2ayfkzMaRWjwYaFiS+kQ@mail.gmail.com>
Date: Wed, 6 Nov 2024 11:31:52 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Jeffrey Vander Stoep <jeffv@...gle.com>
Subject: Re: [PATCH] rust: platform: add Io support

On Thu, Oct 24, 2024 at 4:20 PM Daniel Almeida
<daniel.almeida@...labora.com> wrote:
> +    /// Maps a platform resource through ioremap() where the size is known at
> +    /// compile time.
> +    pub fn ioremap_resource_sized<const SIZE: usize>(
> +        &self,
> +        resource: u32,
> +    ) -> Result<Devres<IoMem<SIZE>>> {
> +        let res = self.resource(resource)?;
> +        let size = self.resource_len(resource)? as usize;
> +
> +        // SAFETY: `res` is guaranteed to be a valid MMIO address and the size
> +        // is given by the kernel as per `self.resource_len()`.
> +        let io = unsafe { IoMem::new(res as _, size) }?;

This cast looks wrong to me. You're taking a pointer to `struct
resource` and casting that to an MMIO address? Shouldn't the address
be (*res).start?

Danilo already mentioned this, but I think you're missing a call to
`request_mem_region` as well.

> +        let devres = Devres::new(self.as_ref(), io, GFP_KERNEL)?;

What purpose does the Devres serve?

Alice