Re: [PATCH 2/4] rust: device: implement device context marker

[Benno Lossin <benno.lossin@proton.me>]

On Thu Mar 13, 2025 at 3:13 AM CET, Danilo Krummrich wrote:
> Some bus device functions should only be called from bus callbacks,
> such as probe(), remove(), resume(), suspend(), etc.
>
> To ensure this add device context marker structs, that can be used as
> generics for bus device implementations.
>
> Suggested-by: Benno Lossin <benno.lossin@proton.me>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

I would have folded this into #3, but if you prefer it being split, then
it's also fine.

> ---
>  rust/kernel/device.rs | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
> index db2d9658ba47..39793740a95c 100644
> --- a/rust/kernel/device.rs
> +++ b/rust/kernel/device.rs
> @@ -209,6 +209,24 @@ unsafe impl Send for Device {}
>  // synchronization in `struct device`.
>  unsafe impl Sync for Device {}
>  
> +/// Marker trait for the context of a bus specific device.
> +///
> +/// Some functions of a bus specific device should only be called from a certain context, i.e. bus
> +/// callbacks, such as `probe()`.
> +///
> +/// This is the marker trait for structures representing the context of a bus specific device.
> +pub trait DeviceContext {}

I would make this trait sealed. ie:

    pub trait DeviceContext: private::Sealed {}
    
    mod private {
        pub trait Sealed {}

        impl Sealed for super::Core {}
        impl Sealed for super::Normal {}
    }

Since currently a user can create a custom context (it will be useless,
but then I think it still is better to give them a compile error).

If you make it sealed,

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

---
Cheers,
Benno

> +
> +/// The [`Normal`] context is the context of a bus specific device when it is not an argument of
> +/// any bus callback.
> +pub struct Normal;
> +impl DeviceContext for Normal {}
> +
> +/// The [`Core`] context is the context of a bus specific device when it is supplied as argument of
> +/// any of the bus callbacks, such as `probe()`.
> +pub struct Core;
> +impl DeviceContext for Core {}
> +
>  #[doc(hidden)]
>  #[macro_export]
>  macro_rules! dev_printk {