linux-kernel - Re: [PATCH v15 2/3] rust: io: mem: add a generic iomem abstraction

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Message-Id: <19218014-4C48-4BE4-AE27-1DD309F8245F@collabora.com>
Date: Fri, 18 Jul 2025 09:23:26 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Danilo Krummrich <dakr@...nel.org>
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 <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v15 2/3] rust: io: mem: add a generic iomem abstraction

Hi Danilo,

> On 17 Jul 2025, at 16:45, Danilo Krummrich <dakr@...nel.org> wrote:
> 
> On Thu Jul 17, 2025 at 5:55 PM CEST, Daniel Almeida wrote:
>> +impl<const SIZE: usize> IoMem<SIZE> {
>> +    fn ioremap(resource: &Resource) -> Result<Self> {
>> +        // Note: It looks like there aren't any 32-bit architectures that define
>> +        // ioremap_np. This means that sometimes this conversion will fail. If
>> +        // we performed a lossy cast, i.e., using `as`, then `bindings::ioremap`
>> +        // would return NULL anyway.
> 
> Why would ioremap() return NULL if you perform a lossy cast?
> 
> Anyways, I find it a bit difficult to decode the actual problem from the above
> description.
> 
> I feel it would be better to just explain that some ioremap() implementations
> use types that depend on the CPU word width rather than the bus address width.
> 
> If you agree, no need to resend though, we can change it when applying the
> series.
> 
>> +        // TODO: Properly address this in the C code to avoid this `try_into`.
>> +        let size = resource.size().try_into()?;
>> +        if size == 0 {
>> +            return Err(EINVAL);
>> +        }
> 

Ok, I do agree that what you said is better. Feel free to use it then.

— Daniel