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

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Message-ID: <521C49EF.5020403@overkiz.com>
Date:	Tue, 27 Aug 2013 08:40:47 +0200
From:	boris brezillon <b.brezillon@...rkiz.com>
To:	Stephen Warren <swarren@...dotorg.org>
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 27/08/2013 05:57, Stephen Warren wrote:
> 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?
>

Do you mean something like:

atmel,pins = <xxx>;                /* current dt binding */
atmel,generic-pins = <yyy>;    /* new dt binding */

If that's what you had in mind, it will be a little bit tricky to 
handle, because AFAIK the pinconf_ops
callbacks do not give me any element I could use to deduce the type of 
pinconf (generic or
native).
This implies I have to know early during the probe process which kind of 
binding is in use.

Please tell me if I missed some key points, and this can be easily done.


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