linux-kernel - Re: [PATCH v11 1/4] rust: io: add resource abstraction

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Message-Id: <4DF66D6F-C89E-4472-AB76-B3EB1CB6F07C@collabora.com>
Date: Wed, 2 Jul 2025 15:11:04 -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>,
 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>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 Ying Huang <huang.ying.caritas@...il.com>,
 Benno Lossin <lossin@...nel.org>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org,
 Fiona Behrens <me@...enk.dev>
Subject: Re: [PATCH v11 1/4] rust: io: add resource abstraction

Hi Danilo

> On 2 Jul 2025, at 07:21, Danilo Krummrich <dakr@...nel.org> wrote:
> 
>> +#[cfg(CONFIG_HAS_IOPORT)]
>> +/// Returns a reference to the global `ioport_resource` variable.
>> +pub fn ioport_resource() -> &'static Resource {
>> +    // SAFETY: `bindings::ioport_resoure` has global lifetime and is of type Resource.
>> +    unsafe { Resource::as_ref(&raw mut bindings::ioport_resource) }
>> +}
>> +
>> +#[cfg(CONFIG_HAS_IOMEM)]
>> +/// Returns a reference to the global `iomem_resource` variable.
>> +pub fn iomem_resource() -> &'static Resource {
>> +    // SAFETY: `bindings::iomem_resoure` has global lifetime and is of type Resource.
>> +    unsafe { Resource::as_ref(&raw mut bindings::iomem_resource) }
>> +}
> 
> This caught my attention, and I have a few questions:
> 
>  1) What do you need them for? I don't see any methods that would usually
>     consume those.
> 
>  2) Why are they behind CONFIG_HAS_IOPORT and CONFIG_HAS_IOMEM, even though the
>     C instances are not?
> 
>  3) What happens if we pass them to IoMem::new()? Is this really safe, or do we
>     need them to be a special Resource type?
> 

Good catch, actually.

I worked on this patch with Fiona and IIRC, she needed access to these two for
her LED abstractions. This patch has seen a few iterations already and this may
or may not be obsolete by now. I must say I've never used these before so I
don't really know how they work nor do I need this at all.

Fiona, do you still need these two accessors?

— Daniel