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

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Date:   Fri, 16 Apr 2021 15:55:11 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Clemens Gruber <clemens.gruber@...ruber.com>,
        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
Subject: Re: [PATCH v8 4/8] dt-bindings: pwm: Support new PWM_USAGE_POWER flag

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.

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.

Thierry

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