linux-kernel - Re: [PATCH v2 07/10] dt-bindings: adv748x: add information about serial audio interface (I2S/TDM)

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Message-ID: <20200320095907.GB5193@pendragon.ideasonboard.com>
Date:   Fri, 20 Mar 2020 11:59:07 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Alex Riesen <alexander.riesen@...itec.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        driverdevel <devel@...verdev.osuosl.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v2 07/10] dt-bindings: adv748x: add information about
 serial audio interface (I2S/TDM)

Hi Alex,

On Fri, Mar 20, 2020 at 10:03:39AM +0100, Alex Riesen wrote:
> Geert Uytterhoeven, Fri, Mar 20, 2020 09:48:14 +0100:
> > On Fri, Mar 20, 2020 at 9:44 AM Alex Riesen <alexander.riesen@...itec.com> wrote:
> > > Laurent Pinchart, Thu, Mar 19, 2020 19:01:25 +0100:
> > > > On Thu, Mar 19, 2020 at 06:42:36PM +0100, Alex Riesen wrote:
> > > > > As the driver has some support for the audio interface of the device,
> > > > > the bindings file should mention it.
> > > > >
> > > > > @@ -16,6 +18,8 @@ Required Properties:
> > > > >      slave device on the I2C bus. The main address is mandatory, others are
> > > > >      optional and remain at default values if not specified.
> > > > >
> > > > > +  - #clock-cells: must be <0> if the I2S port is used
> > > >
> > > > Wouldn't it be simpler to set it to 0 unconditionally ?
> > >
> > > Would it? If the port itself is optional, shouldn't the clock be an option
> > > too?
> > 
> > You'd be surprised how many board designers would consider this a cheap
> > 12.288 MHz clock source, without using the I2S port ;-)
> 
> Well, I am :-)
> 
> Especially considering that the driver will not switch the MCLK pin aktive
> (all I2S-related pins are tristate by default).

If the MCLK can't be output without enabling the I2S then I don't mind
if we make the #clock-cells optional, although, as Geert mentioned,
someone may still want to use it.

> And how do I require it to be set unconditionally? By just removing the
> "if ..." part of the statement?

Yes. For YAML it's easy too, the hard part is making properties
conditional :-)

-- 
Regards,

Laurent Pinchart