linux-kernel - Re: [PATCH v8 15/26] pwm: jz4740: Add support for the JZ4725B

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Message-ID: <20181213161831.GC13531@ulmo>
Date:   Thu, 13 Dec 2018 17:18:31 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Malaterre <malat@...ian.org>,
        Ezequiel Garcia <ezequiel@...labora.co.uk>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-clk@...r.kernel.org, od@...c.me
Subject: Re: [PATCH v8 15/26] pwm: jz4740: Add support for the JZ4725B

On Thu, Dec 13, 2018 at 03:03:15PM +0100, Paul Cercueil wrote:
> Hi,
> 
> Le jeu. 13 déc. 2018 à 10:24, Uwe Kleine-König
> <u.kleine-koenig@...gutronix.de> a écrit :
> > Hello,
> > 
> > On Wed, Dec 12, 2018 at 11:09:10PM +0100, Paul Cercueil wrote:
> > >  The PWM in the JZ4725B works the same as in the JZ4740, except that
> > > it
> > >  only has 6 channels available instead of 8.
> > 
> > this driver is probed only from device tree? If yes, it might be
> > sensible to specify the number of PWMs there and get it from there.
> > There doesn't seem to be a generic binding for that, but there are
> > several drivers that could benefit from it. (This is a bigger project
> > though and shouldn't stop your patch. Still more as it already got
> > Thierry's ack.)
> 
> I think there needs to be a proper guideline, as there doesn't seem to be
> a consensus about this. I learned from emails with Rob and Linus (Walleij)
> that I should not have in devicetree what I can deduce from the compatible
> string.

Correct. If the compatible string already defines the number of PWMs
that the hardware exposes, there's no need to explicitly say so again in
DT.

Thierry

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