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

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Message-Id: <D9VTC578EVTH.2HFJ9TNPFW8NQ@kernel.org>
Date: Wed, 14 May 2025 12:31:38 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Mark Brown" <broonie@...nel.org>
Cc: "Daniel Almeida" <daniel.almeida@...labora.com>, "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>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v3] rust: regulator: add a bare minimum regulator
 abstraction

On Wed May 14, 2025 at 12:16 PM CEST, Mark Brown wrote:
> On Wed, May 14, 2025 at 11:37:46AM +0200, Benno Lossin wrote:
>> On Wed May 14, 2025 at 9:46 AM CEST, Mark Brown wrote:
>> > On Tue, May 13, 2025 at 10:01:05PM +0200, Benno Lossin wrote:
>
>> >> This isn't fully clear what it's supposed to mean to me. Maybe mention
>> >> the `regulator_enable` function?
>
>> > I suspect this is adequately clear to someone with the domain specific
>> > knowledge required to be using the API.
>
>> I still think it's useful to name the exact function that is meant by
>> "enabled".
>
> It's not clear to me that it's helpful to have to refer to the C API, as
> opposed to just being free standing.

To me it would be much more clear if the function were named.

>> >> Why don't we drop the refcount if the `regulator_disable` call fails?
>
>> > If you fail to disable the regulator then the underlying C code won't
>> > drop it's reference count.
>
>> So if it fails, the regulator should stay alive indefinitely? Would be
>> useful to explain that in the comment above the `ManuallyDrop`.
>
> Practically speaking if the regulator disable fails the system is having
> an extremely bad time and the actual state of the regulator is not clear.
> Users might want to try some attempt at retrying, one of which could
> possibly succeed in future, but realistically if this happens there's
> something fairly catastrophic going on.  Some critical users might want
> to care and have a good idea what makes sense for them, but probably the
> majority of users of the API aren't going to have a good strategy here.

Makes sense. So does `regulator_disable` take ownership of the refcount?
If yes, then just put that in the comment above the `ManuallyDrop` & in
the `Drop` impl of `EnabledRegulator`.

---
Cheers,
Benno