linux-kernel - Re: [PATCH v2 2/7] pwm: core: Always require PWM flags to be provided

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Message-ID: <20210607095324.yaiu5lzb5zgoejpa@pengutronix.de>
Date:   Mon, 7 Jun 2021 11:53:24 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Flavio Suligoi <f.suligoi@...m.it>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-acpi@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        Lee Jones <lee.jones@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v2 2/7] pwm: core: Always require PWM flags to be provided

Hi Andy,

On Mon, Jun 07, 2021 at 12:02:37PM +0300, Andy Shevchenko wrote:
> On Sun, Jun 06, 2021 at 11:30:54PM +0200, Uwe Kleine-König wrote:
> > Hello Andy,
> > 
> > On Mon, May 31, 2021 at 10:49:42PM +0300, Andy Shevchenko wrote:
> > > It makes little sense to make PWM flags optional since in case
> > > of multi-channel consumer the flags can be optional only for
> > > the last listed channel.
> > 
> > I think the same holds true for dt references.
> 
> Can you elaborate this? I haven't got what you are talking about, not a DT
> expert here.

Ah no, I mixed that up. While the function that parses the phandle is
flexible, for each pwm controller the number of arguments is fixed, so

	pwms = <&pwm1 100000 &pwm2 100000 &pwm3 1000000>;

cannot be interpreted as 3-argument references to two PWMs. This is
different to ACPI (I guess, not an ACPI expert here :-) because &pwm1
"knows" if it needs 1 or 2 additional parameters (#pwm-cells).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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