linux-kernel - Re: [PATCH v4 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-Id: <DAUV31OTE7QC.3R9LSCO61CFR3@kernel.org>
Date: Tue, 24 Jun 2025 17:17:06 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Boqun Feng" <boqun.feng@...il.com>, "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Daniel Almeida" <daniel.almeida@...labora.com>, "Danilo Krummrich"
 <dakr@...nel.org>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...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>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>, "Bjorn
 Helgaas" <bhelgaas@...gle.com>, Krzysztof Wilczy´nski
 <kwilczynski@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] rust: irq: add support for non-threaded IRQs and
 handlers

On Tue Jun 24, 2025 at 4:33 PM CEST, Boqun Feng wrote:
> On Tue, Jun 24, 2025 at 02:50:23PM +0100, Alice Ryhl wrote:
>> On Tue, Jun 24, 2025 at 1:46 PM Benno Lossin <lossin@...nel.org> wrote:
>> > On Tue Jun 24, 2025 at 2:31 PM CEST, Daniel Almeida wrote:
>> > > On 23 Jun 2025, at 16:28, Benno Lossin <lossin@...nel.org> wrote:
>> > >> On Mon Jun 23, 2025 at 9:18 PM CEST, Boqun Feng wrote:
>> > >>>    try_pin_init!(&this in Self {
>> > >>>        handler,
>> > >>>        inner: Devres::new(
>> > >>>            dev,
>> > >>>            RegistrationInner {
>> > >>>                // Needs to use `handler` address as cookie, same for
>> > >>>                // request_irq().
>> > >>>                cookie: &raw (*(this.as_ptr().cast()).handler),
>> > >>>                irq: {
>> > >>>                     to_result(unsafe { bindings::request_irq(...) })?;
>> > >>>  irq
>> > >>> }
>> > >>>             },
>> > >>>             GFP_KERNEL,
>> > >>>        )?,
>> > >>>        _pin: PhantomPinned
>> > >>>    })
>> > >>
>> > >> Well yes and no, with the Devres changes, the `cookie` can just be the
>> > >> address of the `RegistrationInner` & we can do it this way :)
>> > >>
>> > >> ---
>> > >> Cheers,
>> > >> Benno
>> > >
>> > >
>> > > No, we need this to be the address of the the whole thing (i.e.
>> > > Registration<T>), otherwise you can’t access the handler in the irq
>> > > callback.
>
> You only need the access of `handler` in the irq callback, right? I.e.
> passing the address of `handler` would suffice (of course you need
> to change the irq callback as well).
>
>> >
>> > Gotcha, so you keep the cookie field, but you should still be able to
>> > use `try_pin_init` & the devres improvements to avoid the use of
>> > `pin_init_from_closure`.
>> 
>> It sounds like this is getting too complicated and that
>> `pin_init_from_closure` is the simpler way to go.

The current code is not correct and the version that Boqun has below
looks pretty correct (and much simpler).

> Even if we use `pin_init_from_closure`, we still need the other
> `try_pin_init` anyway for `Devres::new()` (or alternatively we can
> implement a `RegistrationInner::new()`).
>
> Below is what would look like with the Devres changes in mind:
>
>
>     try_pin_init!(&this in Self {
>         handler,
>         inner: <- Devres::new(
>             dev,
>             try_pin_init!( RegistrationInner {
>                 // Needs to use `handler` address as cookie, same for
>                 // request_irq().
>                 cookie: &raw (*(this.as_ptr().cast()).handler),
> 		// @Benno, would this "this" work here?

Yes.

>                 irq: {
>                      to_result(unsafe { bindings::request_irq(...) })?;
>                      irq
> 		}
>              }),
>         )?,
>         _pin: PhantomPinned
>     })

---
Cheers,
Benno