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

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Message-Id: <2F3D3A40-6EF9-46FC-A769-E5A3AAF67E65@collabora.com>
Date: Thu, 22 Jan 2026 21:29:30 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Danilo Krummrich <dakr@...nel.org>,
 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 22 Jan 2026, at 10:44, Maxime Ripard <mripard@...nel.org> wrote:
> 
> On Mon, Jan 19, 2026 at 03:37:17PM +0100, Danilo Krummrich wrote:
>> 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'm not sure I'm following what you're saying, sorry. I've pointed out
> such a use-case already.
> 
>>>>> 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?
> 
> 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.
> 
> Maxime

Maxime, I know you’ve already pointed out a use-case, but I think the
confusion stems from why you seem to think that the current solution cannot
cater to the API you mentioned in a clean way. You seem to imply that there
will be a lot of boilerplate involved, but we (or I) cannot see this. Perhaps
it would help if you highlighted how exactly the type state solution would be
verbose using some pseudocode. I guess that would make your point clearer for
us.

— Daniel