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

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Message-Id: <DFSN4FDCYHMW.3J3237PEBV2ZP@kernel.org>
Date: Mon, 19 Jan 2026 15:37:17 +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 Mon Jan 19, 2026 at 3:18 PM CET, Maxime Ripard wrote:
> On Mon, Jan 19, 2026 at 02:13:48PM +0100, Danilo Krummrich wrote:
>> On Mon Jan 19, 2026 at 1:54 PM CET, Daniel Almeida wrote:
>> >> On 19 Jan 2026, at 09:35, Alice Ryhl <aliceryhl@...gle.com> wrote:
>> >> I think that if you still want an API where you just call enable/disable
>> >> directly on it with no protection against unbalanced calls, then that
>> >> should be the special API. Probably called RawClk and functions marked
>> >> unsafe. Unbalanced calls seem really dangerous and use should not be
>> >> encouraged.
>> 
>> +1; and unless there is a use-case that requires otherwise, it should not even
>> be possible to do this at all -- at least for driver code.
>
> I mean, it's great, it's safe, etc. but it's also suboptimal from a PM
> perspective on many platforms. It's totally fine to provide nice, safe,
> ergonomic wrappers for the drivers that don't care (or can't, really),
> but treating a legitimate optimisation as something we should consider
> impossible to do is just weird to me.

I said that an unsafe API with potentially unbalanced calls is something we
should clearly avoid for drivers. This is *not* equivalent to "treating a
legitimate optimisation as something we should consider impossible".

If we discover use-cases where the current API doesn't work well, we can
invenstigate further.

>> > I think we should discourage RawClk if at all possible. But if the consensus
>> > is that we *really* need this easily-abused thing, I can provide a follow-up.
>> 
>> I think we should only do this if there are use-case with no alternative, so far
>> there haven't been any AFAIK.
>
> I don't really care about which alternative we come up with, but look at
> devm_regmap_init_mmio_clk for example. It is a valid use-case that
> already exists today, and has had for more than a decade at this point.

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?