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

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Message-ID: <aFq8tiJfU-KshBIN@cassiopeiae>
Date: Tue, 24 Jun 2025 16:56:54 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Benno Lossin <lossin@...nel.org>,
	Daniel Almeida <daniel.almeida@...labora.com>,
	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 07:42:05AM -0700, Boqun Feng wrote:
> On Tue, Jun 24, 2025 at 07:33:35AM -0700, 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.
> > 
> > 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?
> >                 irq: {
> >                      to_result(unsafe { bindings::request_irq(...) })?;
> >                      irq
> > 		}
> >              }),
> >         )?,
> >         _pin: PhantomPinned
> >     })
> > 
> > 
> 
> Never mind, `dev` is a `Device<Bound>` so it cannot be unbounded during
> the call ;-)

We even know that `dev` won't be unbound as long as the returned
`impl PinInit<Self, Error> + 'a` lives. :)