linux-kernel - Re: [PATCH v3 1/3] rust: clk: use the type-state pattern

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <4DD13AE1-C85F-450F-93F2-C7C75766E518@collabora.com>
Date: Tue, 3 Feb 2026 13:28:15 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>,
 Maxime Ripard <mripard@...nel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 Danilo Krummrich <dakr@...nel.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>,
 Drew Fustini <fustini@...nel.org>,
 Guo Ren <guoren@...nel.org>,
 Fu Wei <wefu@...hat.com>,
 Uwe Kleine-König <ukleinek@...nel.org>,
 Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>,
 Miguel Ojeda <ojeda@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>,
 linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org,
 linux-riscv@...ts.infradead.org,
 linux-pwm@...r.kernel.org,
 linux-clk@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3 1/3] rust: clk: use the type-state pattern

<snip>

>> 
>> The problem with what you have suggested is that the previous state is not
>> consumed if you can clone it, and consuming the previous state is a pretty key
>> element in ensuring you cannot misuse it. For example, here:
>> 
>> let enabled_clk = prepared_clk.clone().enable()?;
>> // do stuff
>> // enabled_clk goes out of scope and releases the enable
>> // ref it had
>> 
>> prepared_clk is still alive.
> 
> That was intentional in this example. Think about a prepared_clk that's
> stored in some driver-internal object, because you want to keep the clk
> prepared at all times between the probe() and unbind(). Then you have
> some sections where you want to briefly enable the clk to access
> registers, and immediately disable it when you're done. The clone()
> here guarantees that the initial prepared_clk stays valid.
> 
> If you were to disable, unprepare and put the clk when enabled_clk goes
> out of scope, you'd go

> 
> let enabled_clk = prepared_clk.enable()?;
> 
> and that would still work, it's just not the same use-case.
> 

Ok, let’s have clone() then.

>> Now, this may not be the end of the world in this
>> particular case, but for API consistency, I'd say we should probably avoid this
>> behavior.
>> 
>> I see that Alice suggested a closure approach. IMHO, we should use that
>> instead.
> 
> The closure, while being useful for the above local clk-enablement
> example, doesn't allow for passing some Clk<Enabled> guard around, like
> you would do with a lock Guard, and I believe that's a useful thing to
> have.

Wdym? You’d still get a &Clk<Enabled> that you can pass around, i.e.:

   self.prepared_clk.with_enabled(|clk: &Clk<Enabled> | {
       ... use registers, pass &Clk<Enabled> as needed
   });

This is now not about clone() vs not clone(), but more about limiting the scope of the
Enabled state, which would cater to the use-case you mentioned IIUC.

— Daniel