Re: [PATCH] rust: irq: add &Device<Bound> argument to irq callbacks

[Daniel Almeida <daniel.almeida@collabora.com>]

> On 21 Jul 2025, at 16:33, Alice Ryhl <aliceryhl@google.com> wrote:
> 
> On Mon, Jul 21, 2025 at 9:14 PM Daniel Almeida
> <daniel.almeida@collabora.com> wrote:
>> 
>> Alice,
>> 
>>> On 21 Jul 2025, at 11:38, Alice Ryhl <aliceryhl@google.com> wrote:
>>> 
>>> When working with a bus device, many operations are only possible while
>>> the device is still bound. The &Device<Bound> type represents a proof in
>>> the type system that you are in a scope where the device is guaranteed
>>> to still be bound. Since we deregister irq callbacks when unbinding a
>>> device, if an irq callback is running, that implies that the device has
>>> not yet been unbound.
>>> 
>>> To allow drivers to take advantage of that, add an additional argument
>>> to irq callbacks.
>>> 
>>> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
>>> ---
>>> This patch is a follow-up to Daniel's irq series [1] that adds a
>>> &Device<Bound> argument to all irq callbacks. This allows you to use
>>> operations that are only safe on a bound device inside an irq callback.
>>> 
>>> The patch is otherwise based on top of driver-core-next.
>>> 
>>> [1]: https://lore.kernel.org/r/20250715-topics-tyr-request_irq2-v7-0-d469c0f37c07@collabora.com
>> 
>> I am having a hard time applying this locally.
> 
> Your irq series currently doesn't apply cleanly on top of
> driver-core-next and requires resolving a minor conflict. You can find
> the commits here:
> https://github.com/Darksonn/linux/commits/sent/20250721-irq-bound-device-c9fdbfdd8cd9-v1/

Ah, we’ve already discussed this, it seems.

> 
>>> ///
>>> /// This function should be only used as the callback in `request_irq`.
>>> unsafe extern "C" fn handle_irq_callback<T: Handler>(_irq: i32, ptr: *mut c_void) -> c_uint {
>>> -    // SAFETY: `ptr` is a pointer to T set in `Registration::new`
>>> -    let handler = unsafe { &*(ptr as *const T) };
>>> -    T::handle(handler) as c_uint
>>> +    // SAFETY: `ptr` is a pointer to `Registration<T>` set in `Registration::new`
>>> +    let registration = unsafe { &*(ptr as *const Registration<T>) };
>>> +    // SAFETY: The irq callback is removed before the device is unbound, so the fact that the irq
>>> +    // callback is running implies that the device has not yet been unbound.
>>> +    let device = unsafe { registration.inner.device().as_bound() };
>> 
>> Where was this function introduced? i.e. I am missing the change that brought
>> in RegistrationInner::device(), or maybe some Deref impl that would make this
>> possible?
> 
> In this series:
> https://lore.kernel.org/all/20250713182737.64448-2-dakr@kernel.org/
> 
>> Also, I wonder if we can't make the scope of this unsafe block smaller?
> 
> I guess we could with an extra `let` statement.
> 
> Alice