linux-kernel - Re: [PATCH v3] rust: regulator: add a bare minimum regulator abstraction

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <DA048ETXB1Q1.3KVZ2FHENWKDL@kernel.org>
Date: Mon, 19 May 2025 13:54:37 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Daniel Almeida" <daniel.almeida@...labora.com>, "Alexandre Courbot"
 <acourbot@...dia.com>
Cc: "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>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Danilo
 Krummrich" <dakr@...nel.org>, "Boris Brezillon"
 <boris.brezillon@...labora.com>, "Sebastian Reichel"
 <sebastian.reichel@...labora.com>, "Liam Girdwood" <lgirdwood@...il.com>,
 "Mark Brown" <broonie@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v3] rust: regulator: add a bare minimum regulator
 abstraction

On Mon May 19, 2025 at 12:52 PM CEST, Daniel Almeida wrote:
>> I just mean the cases where users will want to enable and disable the
>> regulator more frequently than just enabling it at probe time.
>
> This is already possible through kernel::types::Either. 
>
> i.e.: the current design - or the proposed typestate one - can already switch
> back and forth between Regulator and EnabledRegulator. Using Either makes it
> just work, because you can change the variant at runtime without hassle. This
> lets you consume self in an ergonomic way.

Have you tried to write such a use-case using `Either`? My personal
experience with `Either` was pretty horrible, since you always have to
match on it before you can do anything to the values. It's not really
ergonomic.

I think we should remove it, as it also doesn't have any users at the
moment. Anyone that needs it should define a custom enum for their
use-case.

And effectively an `Either<Regulator, EnabledRegulator>` is just a
`Regulator<Switch>` in Alexandre's proposal if I understood it
correctly.

> By the way, the reason I'm pushing back slightly here is because you seem
> (IIUC) to be trying to reintroduce the pattern we had to move away from in v1.
>
> i.e.: we explicitly had to move away from trying to match enables and disables
> in Rust, because it was hard to get this right.
>
> The current design is a simplification that apparently works, because at best
> you have +1 on the count and that is encoded in the type itself, so there is
> nothing to actually "track" or "balance" within a given instance. Multiple
> calls to _get() or _enable() on the same instance are simply forbidden.
>
> Can you add some pseudocode that shows how this doesn't work (or is otherwise
> unergonomic) in Nova? I think it will make your point clearer.

+1 on actual code examples :)

---
Cheers,
Benno