linux-kernel - Re: [PATCH v4 0/1] Change PWM-controlled LED pin active mode and algorithm

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Date:   Thu, 3 Aug 2023 10:43:26 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Nylon Chen <nylon.chen@...ive.com>
CC:     <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-riscv@...ts.infradead.org>, <geert+renesas@...der.be>,
        <pavel@....cz>, <vincent.chen@...ive.com>,
        <emil.renner.berthing@...onical.com>, <aou@...s.berkeley.edu>,
        <palmer@...belt.com>, <paul.walmsley@...ive.com>,
        <krzysztof.kozlowski+dt@...aro.org>, <robh+dt@...nel.org>,
        <conor@...nel.org>, <zong.li@...ive.com>
Subject: Re: [PATCH v4 0/1] Change PWM-controlled LED pin active mode and
 algorithm

Hey Nylon,

(I yoinked the reply to 1/1 to here, as it makes more sense in this
context)

> On Thu, Aug 03, 2023 at 10:15:10AM +0100, Conor Dooley wrote:
> > On Thu, Aug 03, 2023 at 04:57:33PM +0800, Nylon Chen wrote:
> > > According to the circuit diagram of User LEDs - RGB described in themanual hifive-unleashed-a00.pdf[0] and hifive-unmatched-schematics-v3.pdf[1].
> > > 
> > > The behavior of PWM is acitve-high.
> > > 
> > > Removed patches: 1
> > > New patches: (none)
> > > 
> > > Links:
> > > - [0]:  https://sifive.cdn.prismic.io/sifive/c52a8e32-05ce-4aaf-95c8-7bf8453f8698_hifive-unleashed-a00-schematics-1.pdf
> > > - [1]:  https://sifive.cdn.prismic.io/sifive/6a06d6c0-6e66-49b5-8e9e-e68ce76f4192_hifive-unmatched-schematics-v3.pdf
> > > - [2]:  https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf
> > > 
> > > Changed in v4:
> > >  - Remove previous updates to the PWM algorithm.
> > 
> > Why? I don't recall the conclusion on the previous version being that
> > that patch was not needed.
>
> I apologize for forgetting about this update earlier. Just now,
> I tried to pull rebase master and noticed that other developers seem
> to have made some fixes to the algorithm. Upon closer inspection, I
> found that they addressed the part we previously discussed with Emil
> and Uwe, such as "first pwm_apply_state."
> 
> Therefore, my instinct tells me that they have already taken care of
> the issues we discussed before.

I didn't see anything in linux-next that would solve this problem of
inversion. The last meaningful change is:
	commit 334c7b13d38321e47d1a51dba0bef9f4c403ec75
	Author:     Emil Renner Berthing <emil.renner.berthing@...onical.com>
	AuthorDate: Wed Nov 9 12:37:24 2022 +0100
	Commit:     Thierry Reding <thierry.reding@...il.com>
	CommitDate: Mon Jan 30 16:42:45 2023 +0100
	
	    pwm: sifive: Always let the first pwm_apply_state succeed

which predates your v3 by quite a bit.

> I will review the conflicting parts in the pwm-sifive.c code in my v4
> version once again to ensure there are no omissions. If I find any, I
> will submit v5 accordingly.

And if this patch is okay in isolation, please reply here explaining
which commit fixed the algorithm, so that I can pick it up.

Thanks,
Conor.

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