linux-kernel - Re: [PATCH V2 2/2] rust: Add basic bindings for clk APIs

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Message-ID: <CAL_JsqJFeb66pt37wsTB7esCpRD1tpvqP1bvW=Nw8MmP5LvktQ@mail.gmail.com>
Date: Wed, 5 Mar 2025 14:09:51 -0600
From: Rob Herring <robh@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Sebastian Reichel <sebastian.reichel@...labora.com>, Danilo Krummrich <dakr@...nel.org>, 
	Daniel Almeida <daniel.almeida@...labora.com>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...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>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Russell King <linux@...linux.org.uk>, linux-clk@...r.kernel.org, 
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH V2 2/2] rust: Add basic bindings for clk APIs

On Mon, Feb 24, 2025 at 4:00 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 21-02-25, 15:59, Rob Herring wrote:
> > It would be nice to handle the optional case from the start. Otherwise,
> > driver writers handle optional or not optional themselves. The not
> > optional case is typically some form of error message duplicated in
> > every driver.
> >
> > Every foo_get() needs foo_get_optional(), so let's figure out the rust
> > way to handle this once for everyone.
>
> Are we talking about adding another field here (like below code) or
> something else ?

Either way, but generally I think 2 functions are preferred over 1
function and flags.

The harder part here is in C we just return NULL and all subsequent
functions (e.g. clk_enable()) just return with no error for a NULL
struct clk. For rust, I think we'd need a dummy Clk returned and then
handle comparing the passed in reference to the dummy Clk in the rust
bindings.

>
> impl Clk {
>         pub fn get(dev: &Device, name: Option<&CStr>, optional: bool) -> Result<Self> {
>                 ...
>
>                 let clk = if optional {
>                         bindings::clk_get(dev.as_raw(), con_id)
>                 else {
>                         bindings::clk_get_optional(dev.as_raw(), con_id)
>                 };
>
>                 Ok(Self(from_err_ptr(clk)?))
>         }
> }
>
> --
> viresh