linux-kernel - Re: [PATCH v7 3/6] rust: irq: add support for non-threaded IRQs and handlers

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Message-ID: <aIDxFoQV_fRLjt3h@tardis-2.local>
Date: Wed, 23 Jul 2025 07:26:30 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: 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>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>,
	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>,
	Benno Lossin <lossin@...nel.org>, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v7 3/6] rust: irq: add support for non-threaded IRQs and
 handlers

On Wed, Jul 23, 2025 at 10:55:20AM -0300, Daniel Almeida wrote:
> Hi Boqun,
> 
> [...]
> 
> >> +        IrqRequest { dev, irq }
> >> +    }
> >> +
> >> +    /// Returns the IRQ number of an [`IrqRequest`].
> >> +    pub fn irq(&self) -> u32 {
> >> +        self.irq
> >> +    }
> >> +}
> >> +
> >> +/// A registration of an IRQ handler for a given IRQ line.
> >> +///
> >> +/// # Examples
> >> +///
> >> +/// The following is an example of using `Registration`. It uses a
> >> +/// [`AtomicU32`](core::sync::AtomicU32) to provide the interior mutability.
> > 
> > We are going to remove all usage of core::sync::Atomic* when the LKMM
> > atomics [1] land. You can probably use `Completion` here (handler does
> > complete_all(), and registration uses wait_for_completion()) because
> > `Completion` is irq-safe. And this brings my next comment..
> 
> How are completions equivalent to atomics? I am trying to highlight interior
> mutability in this example.
> 

Well, `Completion` also has interior mutability.

> Is the LKMM atomic series getting merged during the upcoming merge window? Because my
> understanding was that the IRQ series was ready to go in 6.17, pending a reply

Nope, it's likely to be in 6.18.

> from Thomas and some minor comments that have been mentioned in v7.
> 
> If the LKMM series is not ready yet, my proposal is to leave the
> Atomics->Completion change for a future patch (or really, to just use the new
> Atomic types introduced by your series, because again, I don't think Completion
> is the right thing to have there).
> 

Why? I can find a few examples that an irq handler does a
complete_all(), e.g. gpi_process_ch_ctrl_irq() in
drivers/dma/qcom/gpi.c. I think it's very normal for a driver thread to
use completions to wait for an irq to happen.

But sure, this and the handler pinned initializer thing is not a blocker
issue. However, I would like to see them resolved as soon as possible
once merged.

Regards,
Boqun

> 
> - Daniel