linux-kernel - Re: [PATCH v2] dt-bindings: pwm: Convert lpc32xx-pwm.txt to YAML

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Message-ID: <b2nlqt3gp4sk7cax722n7t7xonnrjzi6amsfrhylxmurctytiy@yqp7qpttyc5h>
Date: Thu, 13 Mar 2025 08:22:53 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Vladimir Zapolskiy <vz@...ia.com>
Cc: Purva Yeshi <purvayeshi550@...il.com>, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, piotr.wojtaszczyk@...esys.com, 
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dt-bindings: pwm: Convert lpc32xx-pwm.txt to YAML

Hello Vladimir,

On Thu, Mar 13, 2025 at 05:37:44AM +0200, Vladimir Zapolskiy wrote:
> On 3/13/25 00:56, Uwe Kleine-König wrote:
> > Hello,
> > 
> > On Wed, Mar 12, 2025 at 07:59:21PM +0200, Vladimir Zapolskiy wrote:
> > > > +  "#pwm-cells":
> > > > +    const: 3
> > > 
> > > It shall be 1.
> > 
> > No, 3 is the right choice.
> > 
> 
> could you please elaborate?
> 
> I find that here the only configurable parameter is PWM period, so it
> should be sufficient to have one cell only like in marvell,pxa-pwm.yaml
> or google,cros-ec-pwm.yaml.

These two bindings are special snow-flakes and the only drivers that
have #pwm-cells = <1>. Most other bindings use 3 and since commit
895fe4537cc8 ("pwm: Add upgrade path to #pwm-cells = <3> for users of
of_pwm_single_xlate()") (which was created for the pxa driver) the pxa
driver also supports 3 cells. The cros-ec driver even has comment about
that being ugly. 

I intend to convert all bindings to use 3 soon.

While that isn't necessary for each individual piece of hardware to
provide 3 values, having a uniform binding for PWMs provides a nice user
experience and also simplifies matters with nexus nodes (see
e71e46a6f19c ("pwm: Add support for pwm nexus dt bindings")).

Best regards
Uwe

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