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: <98CD0BF6-3350-40B9-B8A9-F569AE3E3220@collabora.com>
Date: Thu, 8 Jan 2026 11:14:37 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>,
 Danilo Krummrich <dakr@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 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

Hi Maxime :)

> 
> I don't know the typestate pattern that well, but I wonder if we don't
> paint ourselves into a corner by introducing it.
> 
> While it's pretty common to get your clock from the get go into a state,
> and then don't modify it (like what devm_clk_get_enabled provides for
> example), and the typestate pattern indeed works great for those, we

Minor correction, devm_clk_get_enabled is not handled by the typestate
pattern. The next patch does include this function for convenience, but
you get a Result<()>. The typestate pattern is used when you want more
control.

> also have a significant number of drivers that will have a finer-grained
> control over the clock enablement for PM.
> 
> For example, it's quite typical to have (at least) one clock for the bus
> interface that drives the register, and one that drives the main
> component logic. The former needs to be enabled only when you're
> accessing the registers (and can be abstracted with
> regmap_mmio_attach_clk for example), and the latter needs to be enabled
> only when the device actually starts operating.
> 
> You have a similar thing for the prepare vs enable thing. The difference
> between the two is that enable can be called into atomic context but
> prepare can't.
> 
> So for drivers that would care about this, you would create your device
> with an unprepared clock, and then at various times during the driver
> lifetime, you would mutate that state.
> 
> AFAIU, encoding the state of the clock into the Clk type (and thus
> forcing the structure that holds it) prevents that mutation. If not, we
> should make it clearer (by expanding the doc maybe?) how such a pattern
> can be supported.
> 
> Maxime

IIUC, your main point seems to be about mutating the state at runtime? This is
possible with this code. You can just have an enum, for example:

enum MyClocks {
	Unprepared(Clk<Unprepared>),
        Prepared(Clk<Prepared>),
	Enabled(Clk<Enabled>), 
}

In fact, I specifically wanted to ensure that this was possible when writing
these patches, as it’s needed by drivers. If you want to, I can cover that in
the examples, no worries.

Same for Regulator<T>, by the way.

— Daniel