linux-kernel - Re: [PATCH v6 2/6] rust: irq: add flags module

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Message-Id: <49ABD63B-05C6-4FDC-B825-5AA2ED323F1C@collabora.com>
Date: Sat, 12 Jul 2025 13:26:52 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Daniel Sedlak <daniel@...lak.dev>,
 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>,
 Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Benno Lossin <lossin@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org,
 linux-pci@...r.kernel.org
Subject: Re: [PATCH v6 2/6] rust: irq: add flags module

Hi Alice,

> On 4 Jul 2025, at 04:42, Alice Ryhl <aliceryhl@...gle.com> wrote:
> 
> On Fri, Jul 04, 2025 at 08:14:11AM +0200, Daniel Sedlak wrote:
>> Hi Daniel,
>> 
>> On 7/3/25 9:30 PM, Daniel Almeida wrote:
>>> +/// Flags to be used when registering IRQ handlers.
>>> +///
>>> +/// They can be combined with the operators `|`, `&`, and `!`.
>>> +#[derive(Clone, Copy, PartialEq, Eq)]
>>> +pub struct Flags(u64);
>> 
>> Why not Flags(u32)? You may get rid of all unnecessary casts later, plus
>> save some extra bytes.
> 
> It looks like the C methods take an `unsigned long`. In that case, I'd
> probably write the code to match that.
> 
> pub struct Flags(c_ulong);
> 
> and git rid of the cast when calling bindings::request_irq.
> 
> As for all the constants in this file, maybe it would be nice with a
> private constructor that uses the same type as bindings to avoid the
> casts?
> 
> impl Flags {
>    const fn new(value: u32) -> Flags {
>     ...
>    }
> }

Sure, but what goes here? This has to be "value as c_ulong” anyways so it
doesn’t really reduce the number of casts.

We should probably switch to Flags(u32) as Daniel Sedlak suggested. Then
it’s a matter of casting once for bindings::request_irq().

— Daniel