linux-kernel - Re: [PATCH v2 3/4] dt-bindings: update google,cros-ec-pwm documentation

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Date:   Thu, 7 Apr 2022 14:38:55 +0000
From:   Fabio Baltieri <fabiobaltieri@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        chrome-platform@...ts.linux.dev, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] dt-bindings: update google,cros-ec-pwm
 documentation

Hi Rob,

On Wed, Apr 06, 2022 at 10:41:45AM -0500, Rob Herring wrote:
> On Thu, Mar 31, 2022 at 12:58:17PM +0000, Fabio Baltieri wrote:
> > Update google,cros-ec-pwm node documentation to mention the
> > google,use_pwm_type property.
> > 
> > Signed-off-by: Fabio Baltieri <fabiobaltieri@...omium.org>
> > ---
> >  .../devicetree/bindings/pwm/google,cros-ec-pwm.yaml         | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/pwm/google,cros-ec-pwm.yaml b/Documentation/devicetree/bindings/pwm/google,cros-ec-pwm.yaml
> > index 4cfbffd8414a..9c895c990ed8 100644
> > --- a/Documentation/devicetree/bindings/pwm/google,cros-ec-pwm.yaml
> > +++ b/Documentation/devicetree/bindings/pwm/google,cros-ec-pwm.yaml
> > @@ -19,6 +19,12 @@ description: |
> >  properties:
> >    compatible:
> >      const: google,cros-ec-pwm
> > +
> > +  google,use-pwm-type:
> > +    description:
> > +      Use PWM types (CROS_EC_PWM_DT_<...>) instead of generic channels.
> > +    type: boolean
> 
> Either do a new compatible string if the cell interpretation is mutually 
> exclusive (channel number vs. type) or split the number space for the 
> 1st cell between type and channel number. IOW, set a bit (31?) to 
> signify the number is a type, not a channel.

Split the number space was my first (tentative) implementation as well,
but it turns out that the PWM subsystem really wants channels to be
zero-based[1], so I don't think flags or bitmasks are really an option.

New compatible sounds good though, I'll rework a v3 with that change.

Thanks!
Fabio

[1] https://elixir.bootlin.com/linux/v5.17/source/drivers/pwm/core.c#L423

-- 
Fabio Baltieri