linux-kernel - Re: [PATCH RFC 2/3] rust: Add bindings for device properties

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Message-ID: <CAH5fLggCDiKUu_dvJZeJr8UD5RvUpqRJbdYKf1F3_MvCdOVK6g@mail.gmail.com>
Date: Wed, 30 Oct 2024 09:15:02 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Rob Herring <robh@...nel.org>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Saravana Kannan <saravanak@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>, Dirk Behme <dirk.behme@...il.com>, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RFC 2/3] rust: Add bindings for device properties

On Tue, Oct 29, 2024 at 8:35 PM Rob Herring <robh@...nel.org> wrote:
>
> On Tue, Oct 29, 2024 at 1:57 PM Miguel Ojeda
> <miguel.ojeda.sandonis@...il.com> wrote:
> >
> > On Tue, Oct 29, 2024 at 7:48 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
> > >
> > > One option is to define a trait for integers:
>
> Yeah, but that doesn't feel like something I should do here. I imagine
> other things might need the same thing. Perhaps the bindings for
> readb/readw/readl for example. And essentially the crate:num already
> has the trait I need. Shouldn't the kernel mirror that? I recall
> seeing some topic of including crates in the kernel?

You can design the trait to look similar to traits in external crates.
We did that for FromBytes/AsBytes.

I assume you're referring to the PrimInt trait [1]? That trait doesn't
really let you get rid of the catch-all case, and it's not even
unreachable due to the u128 type.

[1]: https://docs.rs/num-traits/0.2.19/num_traits/int/trait.PrimInt.html

> > +1, one more thing to consider is whether it makes sense to define a
> > DT-only trait that holds all the types that can be a device property
> > (like `bool` too, not just the `Integer`s).
> >
> > Then we can avoid e.g. `property_read_bool` and simply do it in `property_read`.
>
> Is there no way to say must have traitA or traitB?

No. What should it do if you pass it something that implements both traits?

If you want a single function name, you'll need one trait.

Alice