linux-kernel - Re: [RFC PATCH 2/3] pinctrl: at91: add support for generic pinconf

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Message-ID: <521C22EA.1050908@wwwdotorg.org>
Date:	Mon, 26 Aug 2013 21:54:18 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	boris brezillon <b.brezillon@...rkiz.com>
CC:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Masanari Iida <standby24x7@...il.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Richard Genoud <richard.genoud@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	James Hogan <james.hogan@...tec.com>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 2/3] pinctrl: at91: add support for generic pinconf

On 08/26/2013 12:45 PM, boris brezillon wrote:
> Hello Jean-Christophe,
> 
> Le 26/08/2013 19:53, Jean-Christophe PLAGNIOL-VILLARD a écrit :
>> On 23:37 Sat 24 Aug     , Boris BREZILLON wrote:
>>> Add support for generic pin configuration to pinctrl-at91 driver.
...
>>> a/Documentation/devicetree/bindings/pinctrl/atmel,at91-pinctrl.txt
...
>>> configures various pad settings
>>>   such as pull-up, multi drive, etc.
>>>     Required properties for iomux controller:
>>> -- compatible: "atmel,at91rm9200-pinctrl"
>>> +- compatible: "atmel,at91rm9200-pinctrl" or "atmel,at91sam9x5-pinctrl".
>>> +  Add "generic-pinconf" to the compatible string list to use the
>>> generic pin
...
>>> +pinctrl@...ff400 {
>>> +    #address-cells = <1>;
>>> +    #size-cells = <1>;
>>> +    ranges;
>>> +    compatible = "atmel,at91rm9200-pinctrl", "generic-pinconf",
>>> "simple-bus";
>> nack your break the backword compatibility
>>
>> if we use a old kernel with this new dt nothing will work
>> as the old kernel will never known the the "generic-pinconf" means
>> anything
> 
> Your're right, I didn't think of this case (old kernel with new dt).

Well, just to be clear: If a new DT uses a new compatible value of any
kind, be it adding "generic-pinconf" or switching to "foo-yyy" rather
than "foo-yyy", it won't be compatible... That somewhat implies that you
can't ever replace an old binding with something new.
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