linux-kernel - Re: [PATCH v5 1/9] rust: pwm: Add Kconfig and basic data structures

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Message-ID: <wee6qrsgqojb36pb2ykle5dzlt3x3vscjx6nedy3xlrtdgy3wm@sgduuiflto2p>
Date: Tue, 1 Jul 2025 15:47:51 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Michal Wilczynski <m.wilczynski@...sung.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
	Danilo Krummrich <dakr@...nel.org>, Drew Fustini <drew@...7.com>, Guo Ren <guoren@...nel.org>, 
	Fu Wei <wefu@...hat.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, 
	Marek Szyprowski <m.szyprowski@...sung.com>, Benno Lossin <lossin@...nel.org>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-pwm@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	devicetree@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v5 1/9] rust: pwm: Add Kconfig and basic data structures

Hello Michal,

On Tue, Jul 01, 2025 at 10:24:54AM +0200, Michal Wilczynski wrote:
> On 6/29/25 12:29, Uwe Kleine-König wrote:
> > On Sat, Jun 28, 2025 at 09:47:19PM +0200, Michal Wilczynski wrote:
> 
> >>>>> +    /// Sets the polarity of the PWM signal.
> >>>>> +    pub fn set_polarity(&mut self, polarity: Polarity) {
> >>>>> +        self.0.polarity = polarity.into();
> >>>>> +    }
> >>>>
> >>>> Please don't expose these non-atomic callbacks. pwm_disable() would be
> >>>> fine.
> >>
> >> Hmm, I've just realized that without those setters it would most likely
> >> impossible to correctly implement the get_state callback.
> > 
> > You shouldn't implement the get_state callback for a waveform driver.
> 
> You're right that a new driver using the waveform API shouldn't
> implement .get_state.
> 
> My goal for the abstraction layer, however, is to be flexible enough to
> support writing both modern waveform drivers and legacy style drivers
> that use the .apply and .get_state callbacks.

No, please don't. New C drivers should implement the waveform API. The
same holds true for Rust drivers. So don't create a door that isn't
supposed to be used.

Best regards
Uwe

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