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

From: "Danilo Krummrich" <dakr@kernel.org>
To: "Maxime Ripard" <mripard@kernel.org>
Cc: "Daniel Almeida" <daniel.almeida@collabora.com>,
	"Alice Ryhl" <aliceryhl@google.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
	"Thomas Zimmermann" <tzimmermann@suse.de>,
	"David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Drew Fustini" <fustini@kernel.org>,
	"Guo Ren" <guoren@kernel.org>, "Fu Wei" <wefu@redhat.com>,
	"Uwe Kleine-König" <ukleinek@kernel.org>,
	"Michael Turquette" <mturquette@baylibre.com>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Benno Lossin" <lossin@kernel.org>,
	"Andreas Hindborg" <a.hindborg@kernel.org>,
	"Trevor Gross" <tmgross@umich.edu>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linux-riscv@lists.infradead.org,
	linux-pwm@vger.kernel.org, linux-clk@vger.kernel.org,
	rust-for-linux@vger.kernel.org
Subject: Re: [PATCH v3 1/3] rust: clk: use the type-state pattern
Date: Mon, 19 Jan 2026 15:37:17 +0100	[thread overview]
Message-ID: <DFSN4FDCYHMW.3J3237PEBV2ZP@kernel.org> (raw)
In-Reply-To: <20260119-weightless-pelican-of-anger-190db0@houat>

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@google.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?