linux-kernel - Re: [PATCH RESEND v2] rust: regulator: add a bare minimum regulator abstraction

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Message-Id: <D9ADCA08-C3B3-4964-BDB9-E62A2C7DE85F@collabora.com>
Date: Thu, 27 Mar 2025 08:46:29 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Mark Brown <broonie@...nel.org>
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>,
 lgirdwood@...il.com,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RESEND v2] rust: regulator: add a bare minimum regulator
 abstraction

Hi Mark,

> On 27 Mar 2025, at 08:32, Mark Brown <broonie@...nel.org> wrote:
> 
> On Wed, Mar 26, 2025 at 04:49:26PM -0300, Daniel Almeida wrote:
>>> On 26 Mar 2025, at 15:56, Mark Brown <broonie@...nel.org> wrote:
> 
>>>> +    /// Disables the regulator.
>>>> +    pub fn disable(self) -> Result<Regulator> {
>>>> +        // Keep the count on `regulator_get()`.
>>>> +        let regulator = ManuallyDrop::new(self);
> 
>>> This looks like user code could manually call it which feels like asking
>>> for trouble?
> 
>> Yes, user code can call this. My understanding is that drivers may want to
>> disable the regulator at runtime, possibly to save power when the device is
>> idle?
> 
>> What trouble are you referring to?
> 
> My understanding was that the enable was done by transforming a
> Regulator into an EnabledRegulator but if you can explicitly call
> disable() on an EnabledRegulator without destroying it then you've got
> an EnabledRegulator which isn't actually enabled.  Perhaps it's not
> clear to me how the API should work?

No, you misunderstood a bit, but that’s on me, I should have included examples.

> +impl EnabledRegulator {

> +    /// Disables the regulator.
> +    pub fn disable(self) -> Result<Regulator> 

disable() consumes EnabledRegulator to return Regulator.

Any function that takes 'self' by value (i.e.: “self" instead of “&self” )
effectively kills it. So, in that sense, disable() performs a conversion
between the two types after calling regulator_disable().

— Daniel