Re: [PATCH v2] rust: irq: add support for request_irq()

[Boqun Feng <boqun.feng@gmail.com>]

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@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.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?

Regards,
Boqun

> +    #[pin]
> +    /// Pinned because we need address stability so that we can pass a pointer
> +    /// to the callback.
> +    _pin: PhantomPinned,
> +}
> +

[...]