linux-kernel - Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE

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Date:   Fri, 16 Apr 2021 10:39:12 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Clemens Gruber <clemens.gruber@...ruber.com>,
        Linux PWM List <linux-pwm@...r.kernel.org>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag

On Fri, Apr 16, 2021 at 8:54 AM Thierry Reding <thierry.reding@...il.com> wrote:
>
> On Mon, Apr 12, 2021 at 03:27:41PM +0200, Clemens Gruber wrote:
> > Add the flag and corresponding documentation for PWM_USAGE_POWER.
> >
> > Cc: Rob Herring <robh+dt@...nel.org>
> > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> > ---
> >  Documentation/devicetree/bindings/pwm/pwm.txt | 3 +++
> >  include/dt-bindings/pwm/pwm.h                 | 1 +
> >  2 files changed, 4 insertions(+)
>
> Rob, what are your thoughts on this? I've been thinking about this some
> more and I'm having second thoughts about putting this into device tree
> because it doesn't actually describe a property of the PWM hardware but
> rather a use-case specific hint. It's a bit of a gray area because this
> is just part of the PWM specifier which already has use-case specific
> "configuration", such as the period and the polarity.

I'm pretty neutral. My main hesitation from what I've followed is
'power' seems a bit indirect. A PWM signal doesn't have a 'power' any
more than a GPIO signal does.

> Perhaps a better place for this is within the PWM API? We could add the
> same information into struct pwm_state and then consumers that don't
> care about specifics of the signal (such as pwm-backlight) can set that
> flag when they request a state to be applied.

Yeah, seems like this is fairly well tied to the class of consumer.

Rob