linux-kernel - Re: [PATCH 2/3] iio: potentiometer: mcp4531: Add device tree binding documentation

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Date:	Tue, 21 Jun 2016 09:49:20 +0200
From:	Florian Vaussard <florian.vaussard@...g-vd.ch>
To:	Peter Rosin <peda@...ntia.se>
CC:	Florian Vaussard <florian.vaussard@...il.com>,
	<devicetree@...r.kernel.org>, Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald-Stadler <pmeerw@...erw.net>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Slawomir Stepien <sst@...zta.fm>,
	Joachim Eastwood <manabian@...il.com>,
	Matt Ranostay <mranostay@...il.com>,
	Cristina Moraru <cristina.moraru09@...il.com>,
	<linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] iio: potentiometer: mcp4531: Add device tree binding
 documentation

Hello,

On 06/21/2016 09:38 AM, Peter Rosin wrote:
> On 2016-06-21 08:55, Florian Vaussard wrote:
>> Add the device tree documentation for all the supported parts. Apart the
>> compatible string and standard I2C binding, no other binding is currently
>> needed.
>>
>> Signed-off-by: Florian Vaussard <florian.vaussard@...g-vd.ch>
>> ---
>>  .../bindings/iio/potentiometer/mcp4531.txt         | 84 ++++++++++++++++++++++
>>  1 file changed, 84 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/iio/potentiometer/mcp4531.txt
>>
>> diff --git a/Documentation/devicetree/bindings/iio/potentiometer/mcp4531.txt b/Documentation/devicetree/bindings/iio/potentiometer/mcp4531.txt
>> new file mode 100644
>> index 0000000..b052299
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/iio/potentiometer/mcp4531.txt
>> @@ -0,0 +1,84 @@
>> +* Microchip MCP453X/454X/455X/456X/463X/464X/465X/466X Digital Potentiometer
>> +  driver
>> +
>> +The node for this driver must be a child node of a I2C controller, hence
>> +all mandatory properties for your controller must be specified. See directory:
>> +
>> +        Documentation/devicetree/bindings/i2c
>> +
>> +for more details.
>> +
>> +Required properties:
>> +	- compatible:  	Must be one of the following, depending on the
>> +			model:
>> +			"microchip,mcp4531-502"
>> +			"microchip,mcp4531-103"
>> +			"microchip,mcp4531-503"
> 
> *snip*
> 
> I'm not directly opposed, but I have used the following and DT booting
> works like a charm here.
> 
> 		mcp4651-104@28 {
> 			compatible = "mcp4651-104";
> 			reg = <0x28>;
> 		};
> 

I was not aware that the i2c subsystem had a facility to match the compatible
string against i2c_device_id. Good to know.

> But, I suppose some DT documentation is not bad, and my understanding of
> the device instantiation process and the i2c/dt interactions are not
> complete, so my DT snippet might be an abomination? I'll leave the
> decision if this is needed to someone with more experience on how other
> drivers handle this.
> 

Your compatible string is missing the vendor ID (microchip). This is the only
objection that I can see to your proposition. Let's wait to hear from a DT
maintainer.

Thanks,
Florian