linux-kernel - Re: [PATCH v2] rust: irq: add support for request

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Message-Id: <3753EBEB-8538-403A-BEFC-768390EB2D9E@collabora.com>
Date: Wed, 14 May 2025 11:44:22 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>,
 ojeda@...nel.org,
 alex.gaynor@...il.com,
 gary@...yguo.net,
 bjorn3_gh@...tonmail.com,
 benno.lossin@...ton.me,
 a.hindborg@...nel.org,
 tmgross@...ch.edu,
 rust-for-linux@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: irq: add support for request_irq()

Hi Alice,

> On 23 Jan 2025, at 06:07, Alice Ryhl <aliceryhl@...gle.com> wrote:
> 
> On Thu, Jan 23, 2025 at 8:18 AM Boqun Feng <boqun.feng@...il.com> wrote:
>> 
>> On Wed, Jan 22, 2025 at 01:39:30PM -0300, Daniel Almeida wrote:
>>> Add support for registering IRQ handlers in Rust.
>>> 
>>> IRQ handlers are extensively used in drivers when some peripheral wants to
>>> obtain the CPU attention. Registering a handler will make the system invoke the
>>> passed-in function whenever the chosen IRQ line is triggered.
>>> 
>>> Both regular and threaded IRQ handlers are supported through a Handler (or
>>> ThreadedHandler) trait that is meant to be implemented by a type that:
>>> 
>>> a) provides a function to be run by the system when the IRQ fires and,
>>> 
>>> b) holds the shared data (i.e.: `T`) between process and IRQ contexts.
>>> 
>>> The requirement that T is Sync derives from the fact that handlers might run
>>> concurrently with other processes executing the same driver, creating the
>>> potential for data races.
>>> 
>>> Ideally, some interior mutability must be in place if T is to be mutated. This
>>> should usually be done through the in-flight SpinLockIrq type.
>>> 
>>> Co-developed-by: Alice Ryhl <aliceryhl@...gle.com>
>>> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
>>> Signed-off-by: Daniel Almeida <daniel.almeida@...labora.com>
>>> ---
>>> 
>>> Changes from v1:
>>> 
>>> - Added Co-developed-by tag to account for the work that Alice did in order to
>>> figure out how to do this without Opaque<T> (Thanks!)
>>> - Removed Opaque<T> in favor of plain T
>> 
>> Hmmm...
>> 
>> [...]
>> 
>>> +#[pin_data(PinnedDrop)]
>>> +pub struct Registration<T: Handler> {
>>> +    irq: u32,
>>> +    #[pin]
>>> +    handler: T,
>> 
>> I think you still need to make `handler` as `!Unpin` because compilers
>> can assume a `&mut T` from a `Pin<&mut Registration>`, am I missing
>> something here?
> 
> The current version operates under the assumption that PhantomPinned
> is enough. But I'm happy to add Aliased here.
> 
> Alice

Aliased? What is this? I can’t find that trait or type anywhere.

— Daniel