linux-kernel - Re: [PATCH 3/4] ARM: pinctrl: Add Broadcom Capri pinctrl driver

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Message-ID: <527835FE.2030102@wwwdotorg.org>
Date:	Mon, 04 Nov 2013 17:04:14 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Heiko Stübner <heiko@...ech.de>,
	Linus Walleij <linus.walleij@...aro.org>
CC:	Sherman Yin <syin@...adcom.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Christian Daudt <bcm@...thebug.org>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	Rob Landley <rob@...dley.net>,
	Grant Likely <grant.likely@...aro.org>,
	Matt Porter <matt.porter@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/4] ARM: pinctrl: Add Broadcom Capri pinctrl driver

On 11/04/2013 04:26 PM, Heiko Stübner wrote:

> I remember we had a discussion about how things like bias-disable explicitly 
> shouldn't have a value, when they are represented in the list-format:
> 
> 		pcfg_pull_none: pcfg_pull_none {
> 			bias-disable;
> 		};
> 
> so a bias-disable = <1> was explicitly "forbidden" [for a lack of a better 
> word]. And it was similar for other options, the parameter not meant to be 
> indicating if they are active but really only setting the "strength" or so.

Pure Boolean values should be represented as a valueless property. If
the property is present, the value is true, otherwise false.

However, pinctrl bindings often don't represent Boolean values, but
rather tri-states, with the following values:

* Don't touch this configuration option at all (missing)
* Enable the option (<1>)
* Disable the option (<0>)

The reason for using tri-states being that you might want to write:

xxx1 {
    pins = <PINA>, <PINB>, <PINC>;
    function = <...>;
    // this node doesn't affect pullup
}
xxx2 {
    pins = <PINA>, <PINB>;
    // this node doesn't affect function
    pull-up = <1>; // change, and enable
}
xxx3 {
    pins = <PINAC>;
    // this node doesn't affect function
    pull-up = <0>; // change, and disable
}

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