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

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Message-ID: <aoprvojsnmkbzmmpgx5wxjqtamnr3jyhyqfcqnwhxulp34gn32@aau57u4cotpe>
Date: Fri, 21 Feb 2025 16:28:18 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Daniel Almeida <daniel.almeida@...labora.com>, 
	Viresh Kumar <viresh.kumar@...aro.org>, 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

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).

> Maybe this only becomes relevant once we write a clk driver itself
> in Rust, but still.

For a clock provider implementation you will mainly use 'struct
clk_hw', which is different from 'struct clk'.

Greetings,

-- Sebastian

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