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

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Message-ID: <20250221215931.GA134397-robh@kernel.org>
Date: Fri, 21 Feb 2025 15:59:31 -0600
From: Rob Herring <robh@...nel.org>
To: Sebastian Reichel <sebastian.reichel@...labora.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Cc: 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 Fri, Feb 21, 2025 at 04:28:18PM +0100, Sebastian Reichel wrote:
> Hi,
> 
> On Fri, Feb 21, 2025 at 03:47:57PM +0100, Danilo Krummrich wrote:
> > On Fri, Feb 21, 2025 at 11:29:21AM -0300, Daniel Almeida wrote:
> > > > On 21 Feb 2025, at 10:56, Danilo Krummrich <dakr@...nel.org> wrote:
> > > > On Fri, Feb 21, 2025 at 12:03:39PM +0530, Viresh Kumar wrote:
> > > >> +/// A simple implementation of `struct clk` from the C code.
> > > >> +#[repr(transparent)]
> > > >> +pub struct Clk(*mut bindings::clk);
> > > > 
> > > > I remember that Stephen explained that NULL is valid value for struct clk. As a
> > > > consequence, all functions implemented for `Clk` have to consider this.
> > > 
> > > I am a bit confused here. If NULL is valid, then why should we have to specifically
> > > consider that in the functions? No functions so far explicitly dereferences that value,
> > > they only pass it to the clk framework.
> > 
> > This was badly phrased, the current implementation does not need to consider it
> > indeed. What I meant is that we have to consider it potentially. Especially,
> > when adding new functionality later on. For instance, when accessing fields of
> > struct clk directly. 
> 
> Just a drive-by comment - the current implementation will never have
> a NULL clock anyways. That is only returned by the clk_get functions
> with the _optional() suffix. You are right now only using clk_get(),
> which will instead returns ERR_PTR(-ENOENT).

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.

Rob