linux-kernel - Re: [PATCH v4 1/3] i2c: cadence: Document device tree bindings

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Date:	Fri, 4 Apr 2014 13:57:44 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Gerhard Sittig <gsi@...x.de>
CC:	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>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Wolfram Sang <wsa@...-dreams.de>,
	Grant Likely <grant.likely@...aro.org>,
	Michal Simek <michal.simek@...inx.com>,
	Harini Katakam <harinik@...inx.com>,
	<devicetree@...r.kernel.org>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-i2c@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 1/3] i2c: cadence: Document device tree bindings

On Fri, 2014-04-04 at 09:17PM +0200, Gerhard Sittig wrote:
> On Thu, 2014-04-03 at 10:59 -0700, Soren Brinkmann wrote:
> > 
> > Add device tree binding documentation for the Cadence I2C controller.
> > 
> > [ ... ]
> > 
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/i2c/i2c-cadence.txt
> > @@ -0,0 +1,21 @@
> > +Binding for the Cadence I2C controller
> > +
> > +Required properties:
> > +  compatible: Compatibility string. Must be 'cdns,i2c-r1p10'.
> > +  clocks: From common clock bindings. Phandle to input clock.
> 
> the usual complaint:  'clocks' items are not just phandles (your
> example even suggests this); either adjust the description to
> something correct, or just refer to the common clock bindings to
> not duplicate their description

I'll figure out something.

> 
> but I guess the I2C controller's binding should explicitly state
> which clocks are required, and you might want to consider
> 'clock-names', too

There is only one clock input. There is no need to overcomplicate things
by adding clock-names.

> 
> > +
> > +Optional properties:
> > +  clock-frequency: Desired operating frequency, in Hz, of the bus (actual may
> > +		   be lower). Defaults to 400000 if not specified.
> 
> is the value default a feature of the Linux implementation, or
> consciously designed to be in the binding spec?  and I agree that
> the default should be the standard I2C speed instead of fast mode

I remove the note regarding the default. It's implementation.

> 
> > +
> > +Example:
> > +
> > +	i2c@...04000 {
> > +		compatible = "cdns,i2c-r1p10";
> > +		clocks = <&clkc 38>;
> > +		interrupts = <0 25 4>;
> > +		reg = <0xE0004000 0x1000>;
> > +		clock-frequency = <400000>;
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +	};
> 
> use lower case hex digits, consider symbolic identifiers for
> clocks and interrupt flags

I don't care about the case of those hex digits, but where does it say
that they have to be lower case? Will somebody complain about usage of
lower case chars next?

> 
> the example has many more properties than the binding describes,
> the additional items aren't even optional -- you might want to
> refer to a few more common or general bindings

Well, this is common across binding documentation. Can we please get
consistency in this? I see plenty of binding docs that are documented
this way, not mentioning much regarding such common properties.

	Sören


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