linux-kernel - Re: [PATCH 5/9] ARM: at91/dt: add mmc0 slot0 support to at91rm9200ek board

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Date:	Thu, 12 Dec 2013 18:52:19 +0100
From:	Linus Walleij <linus.walleij@...aro.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>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Russell King <linux@....linux.org.uk>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Joachim Eastwood <manabian@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 5/9] ARM: at91/dt: add mmc0 slot0 support to at91rm9200ek board

On Mon, Dec 9, 2013 at 11:34 AM, boris brezillon
<b.brezillon@...rkiz.com> wrote:
> [Me]
>> This has been suggested under the name "GPIO hogs" in the past.
>>
>> It would work similar to how pinctrl hogs work by associating the
>> GPIO line the controller itself, using some specific string
>> like gpio-input-hogs = <...> / gpio-output-hogs = <...>;
>>
>> The gpiolib core will then grab and set up these before
>> returning from the registration call so noone ever gets a chance
>> to use them.
>
> One more question, and I'm done :).
>
> In which case should we use output-high or output-low config
> instead of gpio-output-hogs ?

This is specified in Documentation/pinctrl.txt under the
heading "GPIO mode pitfalls".

Basically: the generic pinconfig output-high/output-low are
for the case where this is a valid state for a Linux device
driver driving a piece of hardware, like an IP-block, which
is making use of these pins and during that usecase passes
through states the data sheet may call "GPIO mode",
but which are actually a way which the *device* uses
the pins, not independent GPIO lines, like, just some
1-bit line.

Yours,
Linus Walleij
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