Re: [PATCH] rust: clk: use the type-state pattern

[Daniel Sedlak <daniel@sedlak.dev>]

Hi Daniel,

On 7/29/25 11:38 PM, Daniel Almeida wrote:
> +    mod private {
> +        pub trait Sealed {}
> +
> +        impl Sealed for super::Unprepared {}
> +        impl Sealed for super::Prepared {}
> +        impl Sealed for super::Enabled {}
> +    }

I just noticed we have plenty of Sealed traits scattered across rust/ 
folder. Do you think we would benefit from unifying it to a single 
location to prevent duplication?

> +
> +    /// A trait representing the different states that a [`Clk`] can be in.
> +    pub trait ClkState: private::Sealed {
> +        /// Whether the clock should be disabled when dropped.
> +        const DISABLE_ON_DROP: bool;
> +
> +        /// Whether the clock should be unprepared when dropped.
> +        const UNPREPARE_ON_DROP: bool;
> +    }
> +
> +    /// A state where the [`Clk`] is not prepared and not enabled.
> +    pub struct Unprepared;
> +
> +    /// A state where the [`Clk`] is prepared but not enabled.
> +    pub struct Prepared;
> +
> +    /// A state where the [`Clk`] is both prepared and enabled.
> +    pub struct Enabled;

I would put a private member into the structs so the user of this API 
cannot construct it themself without using your abstractions.

	pub struct Unprepared(());
	pub struct Prepared(());
	pub struct Enabled(());

> +
> +    impl ClkState for Unprepared {
> +        const DISABLE_ON_DROP: bool = false;
> +        const UNPREPARE_ON_DROP: bool = false;
> +    }
> +
> +    impl ClkState for Prepared {
> +        const DISABLE_ON_DROP: bool = false;
> +        const UNPREPARE_ON_DROP: bool = true;
> +    }
> +
> +    impl ClkState for Enabled {
> +        const DISABLE_ON_DROP: bool = true;
> +        const UNPREPARE_ON_DROP: bool = true;
> +    }
> +
> +    /// An error that can occur when trying to convert a [`Clk`] between states.
> +    pub struct Error<State: ClkState> {

Nit: IMO we mostly use the `where` variant instead of the colon.

	pub struct Error<State>
	where State: ClkState

But does it make sense to put the bounds on the structs? Shouldn't be 
enough but but the bounds on the impl block?

> +        /// The error that occurred.
> +        pub error: kernel::error::Error,
> +
> +        /// The [`Clk`] that caused the error, so that the operation may be
> +        /// retried.
> +        pub clk: Clk<State>,
> +    }
>   

Thanks!
Daniel