linux-kernel - Re: [PATCH] pinctrl: samsung: Allow pin value to be initialized using pinfunc.

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Date:	Mon, 25 Nov 2013 15:34:19 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Kyungmin Park <kmpark@...radead.org>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Doug Anderson <dianders@...omium.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Heiko Stübner <heiko@...ech.de>,
	Tomasz Figa <t.figa@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] pinctrl: samsung: Allow pin value to be initialized using pinfunc.

On Wed, Nov 20, 2013 at 1:02 AM, Kyungmin Park <kmpark@...radead.org> wrote:
> On Wed, Nov 20, 2013 at 4:16 AM, Stephen Warren <swarren@...dotorg.org> wrote:

>> I think that last point should be addressed by having a driver that owns
>> the GPIO set it to the desired output level, and the implementation of

> Some pins are not connected (NC). At that cases, there's no drivers to
> handle it. To reduce power leakage, it sets proper configuration with
> values instead of reset values.

This is correspondant to the PIN_CONFIG_OUTPUT from
include/linux/pinctrl/pinconf-generic.h

I.e. driving a pin - any pin, even one that cannot do GPIO - high
or low as default.

One could argue that if you can drive the pin high/low using
software then by definition it *is* GPIO. Even if it cannot trigger
IRQs or anything.

The rationale for having it in pinconf-generic is basically for
use cases such that one of the the pin config states the device
pass through may relate to what the documentation calls
the "GPIO mode fallacy" - a state on the pins that is definately
related to the use case of a certain device, but puts the pin
in something the manual calls "GPIO mode" in order to save
power.

But from a use case point of view that is not GPIO, it is the
typically the sleep state of a certain pin when used with a
certain device.

I'll see if I can think of some doc patch to make this more clear...

Yours,
Linus Walleij
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