Re: [RFC PATCH 07/13] dt-bindings: i2c: Add support for 'i2c-bus' subnode

From: Thierry Reding <thierry.reding@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Alexandre Courbot <gnurou@gmail.com>,
	Stephen Warren <swarren@wwwdotorg.org>,
	Wolfram Sang <wsa@the-dreams.de>,
	dri-devel@lists.freedesktop.org,
	Jon Hunter <jonathanh@nvidia.com>,
	linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org
Subject: Re: [RFC PATCH 07/13] dt-bindings: i2c: Add support for 'i2c-bus' subnode
Date: Fri, 17 Jun 2016 18:45:25 +0200	[thread overview]
Message-ID: <20160617164525.GL27475@ulmo.ba.sec> (raw)
In-Reply-To: <20160617163054.GD32754@leverpostej>

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On Fri, Jun 17, 2016 at 05:30:54PM +0100, Mark Rutland wrote:
> On Fri, Jun 17, 2016 at 01:03:41PM +0100, Jon Hunter wrote:
> > The I2C driver core for boards using device-tree assumes any subnode of
> > an I2C adapter in the device-tree blob as being a I2C slave device.
> > Although this makes complete sense, some I2C adapters may have subnodes
> > which are not I2C slaves but subnodes presenting other features. For
> > example some Tegra devices have an I2C interface which may share its
> > pins with other devices and to share these pins subnodes for
> > representing these pins so they have be shared via the pinctrl framework
> > are needed.
> > 
> > To allow I2C adapters to have non-I2C specific subnodes in device-tree
> > that are not parsed by the I2C driver core by adding support for a
> > 'i2c-bus' subnode where I2C slaves can be placed. If the 'i2c-bus'
> > subnode is present then all I2C slaves must be placed under this subnode.
> > 
> > Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
> > ---
> >  Documentation/devicetree/bindings/i2c/i2c.txt | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt
> > index f31b2ad1552b..ed56b08c7e6e 100644
> > --- a/Documentation/devicetree/bindings/i2c/i2c.txt
> > +++ b/Documentation/devicetree/bindings/i2c/i2c.txt
> > @@ -32,6 +32,14 @@ wants to support one of the below features, it should adapt the bindings below.
> >  - clock-frequency
> >  	frequency of bus clock in Hz.
> >  
> > +- i2c-bus
> > +	For I2C adapters that have child nodes that are a mixture of both I2C
> > +	devices and non-I2C devices (such as a pin controller), the 'i2c-bus'
> > +	subnode can be used for populating I2C devices to prevent the I2C core
> > +	from attempting to add any non-i2c nodes as I2C devices. If 'i2c-bus'
> > +	subnode is present then all I2C slaves must be added under this
> > +	subnode.
> 
> The general idea seems sound.
> 
> It would be good if we could remove the mention of the I2C core,
> something like:
> 
>   - i2c-bus
> 	For I2C adapters that have child nodes that are a mixture of both I2C
> 	devices and non-I2C devices (such as a pin controller), the 'i2c-bus'
> 	subnode can be used for populating I2C devices. If an 'i2c-bus'
> 	subnode is present, only subnodes of this will be considered as
> 	I2C slaves.
> 
> How are #address-cells and #size-cells handled in this case? I assume
> that they should live under the i2c-bus subnode, which should be called
> out.

Good catch. Yes, I think the i2c-bus subnode would be the right place
for #address-cells and #size-cells.

Thierry

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