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Date:   Wed, 11 Jul 2018 16:45:29 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Wolfram Sang <wsa@the-dreams.de>, linux-i2c@vger.kernel.org,
        Jonathan Corbet <corbet@lwn.net>,
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        Rafal Ciepiela <rafalc@cadence.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Nishanth Menon <nm@ti.com>, Rob Herring <robh+dt@kernel.org>,
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        Przemyslaw Gaj <pgaj@cadence.com>
Subject: Re: [PATCH v5 04/10] dt-bindings: i3c: Document core bindings
Message-ID: <20180711164529.3388d045@bbrezillon>
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On Wed, 11 Jul 2018 16:10:10 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> On Fri, Jun 22, 2018 at 12:49 PM, Boris Brezillon
> <boris.brezillon@bootlin.com> wrote:
> > A new I3C subsystem has been added and a generic description has been
> > created to represent the I3C bus and the devices connected on it.
> >  
> 
> > +I2C devices
> > +===========
> > +
> > +Each I2C device connected to the bus should be described in a subnode. All
> > +properties described in Documentation/devicetree/bindings/i2c/i2c.txt are
> > +valid here, but several new properties have been added.
> > +
> > +New constraint on existing properties:
> > +--------------------------------------  
> ...
> > +  + third cell: should be 0  
> 
> What for? Just to be future-proof, or do you have something specific
> in mind here?

Even if I2C devices only need 1 cell, I3C devices need 3 (1 for the
static address and 2 for the PID). Since both type of devices are
described under the same bus node, and we can have different
#address-cells, I had to put 0-padding in the last cell.