linux-kernel - Re: [PATCH v3 1/2] rust: irq: add support for request

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Message-Id: <C6A531ED-B464-46C5-A1B1-BD4A87528CA1@collabora.com>
Date: Wed, 4 Jun 2025 15:32:16 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Alice Ryhl <aliceryhl@...gle.com>,
 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>,
 Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 1/2] rust: irq: add support for request_irq()

So, what is the result of this discussion?

> On 3 Jun 2025, at 07:16, Danilo Krummrich <dakr@...nel.org> wrote:
> 
> On Tue, Jun 03, 2025 at 12:09:05PM +0200, Danilo Krummrich wrote:
>> Yes, we could solve this with a lock as well, but it would be an additional
>> lock, just to maintain the current drop() semantics, which I don't see much
>> value in.
> 
> If we want to keep the current drop() semantics we could use a completion
> instead.
> 
> // Devres::drop()
> revoke_nosync()
> complete()
> 
> // devres_callback
> if !try_revoke() {
> // we end up here if try_revoke() indicates that the object was
> // revoked already
> wait_for_completion()
> }

This looks like what is going on here [0], so should I implement what Alice suggested? i.e.:

> > Based on this, we could imagine something along these lines:
> > 
> > struct RegistrationInner(i32);
> > impl Drop for RegistrationInner {
> > fn drop(&mut self) {
> > free_irq(...);
> > }
> > }
> > 
> > struct Registration<T> {
> > reg: Devres<RegistrationInner>,
> > data: T,
> > }
> > 
> > Here you can access the `data` on the registration at any time without
> > synchronization.

— Daniel

[0] https://lore.kernel.org/rust-for-linux/CANiq72nfOcOGJuktzSpNAUWwekaZ98JL7c1FhMKCjPSG80JMPA@mail.gmail.com/T/#t