Re: [RFC PATCH v3 1/5] rtc: add device selector for rtc_class_ops callbacks

["Benno Lossin" <lossin@kernel.org>]

On Wed Feb 25, 2026 at 5:26 PM CET, Danilo Krummrich wrote:
> For the future we will also be able to support references within initializers to
> other pinned fields, which make things a bit more convinient, so you could do
> things like this:
>
> 	let irq_data = impl_pin_init!(SampleIrqData {
> 	    io <- pdev.iomap_region_sized::<BAR0_SIZE>(0, c"my_rtc/bar0")?,
> 	    hw_variant: VendorVariant::StV1,
> 	});
>
> 	let rtc_data = impl_pin_init!(SampleRtcData {
> 	    irq <- irq::Registration::new(..., irq_data),
> 	    io: &irq.io,
> 	    ...,
> 	});
>
> 	let rtc = rtc::Device::new(dev, rtc_data)?;
>
> Note the additional `io: &irq.io,` in the rtc_data initializer. This would be
> legal as we know that `irq` is pinned within `rtc_data`, hence it is valid to
> hold a reference to one of its pinned fields.
>
> I am not sure how far we are from having this supported, I assume Benno and Gary
> can say more about this.

We added that support in 42415d163e5d ("rust: pin-init: add references
to previously initialized fields"). Note that any references created
during the initializer are only valid inside of that initializer. You
can convert into a raw pointer though and if the struct is `!Unpin` it
is sound to use that pointer at the same time as references to the
pinned value.

Cheers,
Benno