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Date: Wed, 4 Jun 2025 20:57:12 +0200
From: Danilo Krummrich <dakr@kernel.org>
To: Daniel Almeida <daniel.almeida@collabora.com>
Cc: Alice Ryhl <aliceryhl@google.com>, Miguel Ojeda <ojeda@kernel.org>,
	Alex Gaynor <alex.gaynor@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@kernel.org>,
	Trevor Gross <tmgross@umich.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
	rust-for-linux@vger.kernel.org
Subject: Re: [PATCH v3 1/2] rust: irq: add support for request_irq()
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In-Reply-To: <C6A531ED-B464-46C5-A1B1-BD4A87528CA1@collabora.com>

On Wed, Jun 04, 2025 at 03:32:16PM -0300, Daniel Almeida wrote:
> So, what is the result of this discussion?
> 
> > On 3 Jun 2025, at 07:16, Danilo Krummrich <dakr@kernel.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.

Yes, I think that's the best approach. You can also have a look at [1], which
implements this approach for misc device already, even though it's slightly more
complicated.

[1] https://lore.kernel.org/lkml/20250530142447.166524-6-dakr@kernel.org/

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