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

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Message-ID: <521C23AF.2060309@wwwdotorg.org>
Date:	Mon, 26 Aug 2013 21:57:35 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	boris brezillon <b.brezillon@...rkiz.com>
CC:	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>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	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 11:17 AM, boris brezillon wrote:
> On 26/08/2013 18:53, Stephen Warren wrote:
>> On 08/24/2013 03:37 PM, Boris BREZILLON wrote:
>>> Add support for generic pin configuration to pinctrl-at91 driver.
>>> diff --git
>>> a/Documentation/devicetree/bindings/pinctrl/atmel,at91-pinctrl.txt
>>> b/Documentation/devicetree/bindings/pinctrl/atmel,at91-pinctrl.txt
>>>   Required properties for iomux controller:
>>> -- compatible: "atmel,at91rm9200-pinctrl"
>>> +- compatible: "atmel,at91rm9200-pinctrl" or "atmel,at91sam9x5-pinctrl".
>> You seem to also be adding a second chip name to the list here, which is
>> more than the patch subject/description imply you're doing...
> 
> This is an update of the documentation:
> "atmel,at91sam9x5-pinctrl" compatible is already used in the pinctrl
> driver but the documention
> was not updated.
> 
> But I agree, this should not be part of this series.
> 
>>> +  Add "generic-pinconf" to the compatible string list to use the
>>> generic pin
>>> +  configuration syntax.
>> "generic-pinconf" is too generic of a compatible value for this binding
>> to define.
>>
>> Instead, I think you want to either:
>>
>> a)
>>
>> Use compatible="atmel,at91rm9200-pinctrl" for the old binding,
>> use compatible="atmel,at91rm9200-pinctrl-generic" for the new binding
>>
>> or:
>>
>> b)
>>
>> Define Boolean property atmel,generic-pinconf (perhaps a better name
>> could be chosen?). If it's not present, parse the node assuming the old
>> binding. If it is present, parse the node assuming the new binding.
>>
> Okay.
> 
> I thought this property string could be generic as it may concern other
> drivers too
> (in order to keep compatibility with old dt ABI and add support the
> generic pinconf binding).
> 
> Anyway, I prefer the first proposition.
> 
> pinctrl single driver is already using these names:
> 
> |compatible = "pinctrl-single" for non generic pinconf binding
> ||compatible = "pinconf-single" ||for generic pinconf binding|
> 
> So I think we should use something similar:
> 
> |compatible = "atmel,at91xx-pinctrl" for non generic pinconf binding
> ||compatible = "|||atmel,at91xx-|pinconf" ||for generic pinconf binding|
> 
> What do you think ?

Hmmm. It is a little odd to switch out the compatible value and invent a
new binding for the same HW. Isn't it possible to define both sets of
properties in the binding, and have drivers look for either?

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