linux-kernel - Re: [PATCH 3/4] pinctrl: Add support for additional dynamic states

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Date:	Wed, 14 Aug 2013 18:41:09 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Tony Lindgren <tony@...mide.com>,
	Linux-OMAP <linux-omap@...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 3/4] pinctrl: Add support for additional dynamic states

On Tue, Jul 30, 2013 at 12:01 AM, Stephen Warren <swarren@...dotorg.org> wrote:

> I was thinking more about people writing the device trees that define
> these states; they need to explicitly make the choice re: overlapping
> states or independent states. We should not plan to obsolete any current
> usage of overlapping states since that will mean an incompatible change
> to the DT ABI (deprecate yes so that no more usage is added, but the
> kernel should still support the old way).

This is another reason to not group and encode explicitly the pins
that remain unchanged during state transitions.

I prefer that either:

- when we build up the state containers in the subsystem,
 we identify overlapping pins and encode them in the state
 container somehow

or:

- when transitioning from state A -> state B we identify
 ovelapping pins or groups of pins and do not touch them
 by making calls down to the driver ->free() and ->request()
 callback pair.

or:

the pinctrl-single.c driver in it's callbacks like ->enable()
->disable(), ->request(), ->free() internally short cuts from
its knowledge of such pin shortcuts and no other drivers
are affected (nor helped) by this optimization.

Yours,
Linus Walleij
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