linux-kernel - Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-Id: <DBCJ3U18L8UL.1A93V6DZ764FR@kernel.org>
Date: Tue, 15 Jul 2025 11:41:53 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Daniel Almeida" <daniel.almeida@...labora.com>, "Danilo Krummrich"
 <dakr@...nel.org>
Cc: "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>,
 "Alice Ryhl" <aliceryhl@...gle.com>, "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 Wilczyński
 <kwilczynski@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v6 3/6] rust: irq: add support for non-threaded IRQs and
 handlers

On Mon Jul 14, 2025 at 5:12 PM CEST, Daniel Almeida wrote:
> Hi,
>
>> 
>>>> 
>>>>  (2) It is guaranteed that the device pointer is valid because (1) guarantees
>>>>      it's even bound and because Devres<RegistrationInner> itself has a
>>>>      reference count.
>>> 
>>> Yeah but I would find it much more natural (and also useful in other
>>> circumstances) if `Devres<T>` would give you access to `Device` (at
>>> least the `Normal` type state).
>> 
>> If we use container_of!() instead or just pass the address of Self (i.e.
>> Registration) to request_irq() instead,
>
>
> Boqun, Benno, are you ok with passing the address of Registration<T> as the cookie?
>
> Recall that this was a change requested in v4, so I am checking whether we are
> all on the same page before going back to that.

I looked at the conversation again and the important part is that you
aren't allowed to initialize the `RegistrationInner` before the
`request_irq` call was successful (because the drop will run
`irq_free`). What pointer you use as the cookie doesn't matter for this.

Feel free to double check again with the concrete code.

---
Cheers,
Benno

> See [0], i.e.:
>
>> > > >> 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).
>
>
> — Daniel
>
> [0] https://lore.kernel.org/all/aFq3P_4XgP0dUrAS@Mac.home/