linux-kernel - Re: [RFC PATCH 2/7] dt-bindings: pwm: document the PWM polarity flag

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Date:   Tue, 17 Mar 2020 18:43:44 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Oleksandr Suvorov <oleksandr.suvorov@...adex.com>
Cc:     devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        Paul Barker <pbarker@...sulko.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Igor Opaniuk <igor.opaniuk@...adex.com>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/7] dt-bindings: pwm: document the PWM polarity flag

On Tue, Mar 17, 2020 at 02:32:26PM +0200, Oleksandr Suvorov wrote:
> Add the description of PWM_POLARITY_NORMAL flag.
> 
> Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@...adex.com>
> ---
> 
>  Documentation/devicetree/bindings/pwm/pwm.txt | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/Documentation/devicetree/bindings/pwm/pwm.txt b/Documentation/devicetree/bindings/pwm/pwm.txt
> index 084886bd721e..440c6b9a6a4e 100644
> --- a/Documentation/devicetree/bindings/pwm/pwm.txt
> +++ b/Documentation/devicetree/bindings/pwm/pwm.txt
> @@ -46,6 +46,7 @@ period in nanoseconds.
>  Optionally, the pwm-specifier can encode a number of flags (defined in
>  <dt-bindings/pwm/pwm.h>) in a third cell:
>  - PWM_POLARITY_INVERTED: invert the PWM signal polarity
> +- PWM_POLARITY_NORMAL: don't invert the PWM signal polarity

This doesn't make sense. PWM_POLARITY_NORMAL is not part of the DT ABI.
The third cell of the specifier is a bitmask of flags.

PWM_POLARITY_NORMAL is an enumeration value that evaluates to 0, so it
makes absolutely no sense as a flag. PWM signals are considered to be
"normal" by default, so no flag is necessary to specify that.

Thierry

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