linux-kernel - Re: Pinmux bindings proposal

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Message-ID: <CAJuYYwQ79o5JuOQfs8rSdasVg+ei4KX7tGLuDA-yysseZya9TA@mail.gmail.com>
Date:	Fri, 20 Jan 2012 21:47:48 +0530
From:	Thomas Abraham <thomas.abraham@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Stephen Warren <swarren@...dia.com>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"Simon Glass (sjg@...omium.org)" <sjg@...omium.org>,
	Dong Aisheng <dongas86@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: Pinmux bindings proposal

On 20 January 2012 15:35, Tony Lindgren <tony@...mide.com> wrote:
> * Thomas Abraham <thomas.abraham@...aro.org> [120119 10:05]:
>> On 19 January 2012 23:50, Tony Lindgren <tony@...mide.com> wrote:
>>
>> I would like to understand the need for populating the
>> pinmux/pingroups tables from dt. The question here is when we have
>> something like
>>
>> pins = <&pinctrl0 0x0030 0x15 0x15 0x7>;
>>
>> which specifies the values that need to be written to the hardware
>> registers, would populating pinmux/pingroup tables from dt required.
>> The SoC specific pinctrl driver can provide a way (with the help of
>> pinctrl core) to translate these values and write to corresponding
>> hardware registers. Is there any particular reason for populating the
>> pinmux/pingroups tables from dt?
>
> Hmm I see. Yes it's still needed as we only want to parse the DT once
> because it's slower unless it was one time only configuration during
> init.

Ok. The time spent on searching for the pin-config property can be
reduced by having the device driver (say, i2c) keep a pointer to all
the pinconfig properties in its node. The next time a driver needs to
reconfigure the pins, the search time can be reduced. The time to
parse the property values though would still be applicable. But I
would still not opt to build pinmux/pinconfig/pindesc tables from dt.

>
> If you only need to set pins once during the init, then we could add
> an option for freeing all or most pins after init. That's what we
> have for the current mach-omap2 mux framework as only few pins need
> to be dynamically remuxed. That will require some changes to the
> pinctrl framework though. We would need flags for each pin from DT
> for init_only/dynamic.
>
> Regards,
>
> Tony

Thanks,
Thomas.
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