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

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Message-Id: <DFVW9MS5YLON.CVJDBYQKJ0P6@kernel.org>
Date: Fri, 23 Jan 2026 11:25:15 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Maxime Ripard" <mripard@...nel.org>
Cc: "Daniel Almeida" <daniel.almeida@...labora.com>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Rafael J. Wysocki" <rafael@...nel.org>, "Viresh
 Kumar" <viresh.kumar@...aro.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

On Thu Jan 22, 2026 at 2:44 PM CET, Maxime Ripard wrote:
> On Mon, Jan 19, 2026 at 03:37:17PM +0100, Danilo Krummrich wrote:
>> I don't see the issue with devm_regmap_init_mmio_clk()? It takes a reference
>> count of the clock and prepares it when called and unprepares the clk in drops
>> its reference in regmap_mmio_free_context() called from the devres callback.
>> 
>> That something we can easily do with the current API, no?
>
> The current one, yes. Doing that in the API suggested here would involve
> some boilerplate in all those drivers they don't have right now.

No, I did mean the API suggested here.

If you would implement something like devm_regmap_init_mmio_clk() in Rust with
this API, you'd have some object like

	struct RegmapResource<T: Backend, R: Resource> {
	    map: Regmap<T>,
	    res: R,
	}

and a concrete instance could have the following type

	RegmapResource<MmIo, Clk<Prepared>>

So, eventually you could have:

	fn devm_regmap_init_mmio_clk(dev: &Device<Bound>,  name: &CStr, ...) -> ... {
	    let clk: Clk<Prepared> = Clk::get(dev, name)?;
	    let regmap = RegmapResource::new(..., clk);

	    Devres::new(dev, regmap)
	}

Of course, we would never design the API in this way, as we have generic I/O
backends and register abstractions, and we'd also not have
devm_regmap_init_mmio_clk() as a constructor for a RegmapResource type, but you
get the idea.