linux-kernel - Re: [PATCH v15 0/5] Change PWM-controlled LED pin active mode and algorithm

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Message-ID: <jfql74ayb42fzmakpz4sfyr2mnv62srpzh3ut4tdmnmipwoboy@uxumfy5kq54j>
Date: Thu, 29 May 2025 13:22:47 +0200
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Nylon Chen <nylon.chen@...ive.com>
Cc: Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Samuel Holland <samuel.holland@...ive.com>, linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v15 0/5] Change PWM-controlled LED pin active mode and
 algorithm

Hello Nylon,

On Thu, May 29, 2025 at 11:53:38AM +0800, Nylon Chen wrote:
> According to the circuit diagram of User LEDs - RGB described in the
> manual hifive-unleashed-a00.pdf[0] and hifive-unmatched-schematics-v3.pdf[1].
> 
> The behavior of PWM is acitve-high.
> 
> According to the descriptionof PWM for pwmcmp in SiFive FU740-C000 Manual[2].
> 
> The pwm algorithm is (PW) pulse active time  = (D) duty * (T) period.
> The `frac` variable is pulse "inactive" time so we need to invert it.
> 
> So this patchset removes active-low in DTS and adds reverse logic to the driver.

Applied to

	https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux.git pwm/for-nexxt

as 6.17-rc1 material. I pondered if this should go in earlier and/or
should get marked for stable. I'm unsure and willing to consider input
here. The problem I see is that while this is a fix, the change is a
breaking one and you need the dts change and the code change applied
either both or none.

Best regards
Uwe

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