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

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Message-id: <1475204.PCyxT0KMui@amdc1227>
Date:	Thu, 05 Dec 2013 18:03:02 +0100
From:	Tomasz Figa <t.figa@...sung.com>
To:	Kevin Bracey <kevin@...cey.fi>
Cc:	Mark Brown <broonie@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Kyungmin Park <kmpark@...radead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Heiko Stübner <heiko@...ech.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Doug Anderson <dianders@...omium.org>,
	"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 Thursday 05 of December 2013 18:49:56 Kevin Bracey wrote:
> On 05/12/2013 17:11, Tomasz Figa wrote:
> > On Thursday 05 of December 2013 15:07:47 Mark Brown wrote:
> >> On Tue, Dec 03, 2013 at 10:29:42AM +0100, Linus Walleij wrote:
> >>
> >>> So a suggested patch to support weak hogs would be interesting
> >>> to look at. Can you provide details on how you think this would
> >>> work?
> >> Or should we be going and applying the default state to all devices on
> >> init without worrying about a driver appearing?
> > If a device isn't used, then it's often better to configure the pins for
> > a different function, such as GPIO, to minimize leakage current.
> >
> 
> And there can also be mutually-exclusive drivers choosing different 
> default states for the same pin. I think you do need a separate "safe" 
> indicator.

That's not quite true, as on a single board you should rather have
a single device node with "okay" status referencing given set of pins.
Still, I think that a separate safe state is the way to go.

> 
> My current thought is that  a late-init "make safe all unclaimed pins" 
> pass would make sense - you can't really mess with pins in an automated 
> fashion on init, as it can mess up bootloader->driver handover.   There 
> already exist late-init "turn off all unclaimed clocks" (at least on 
> shmobile)

That's a feature of Common Clock Framework.

> and "turn off all unclaimed regulators", and it would fit that 
> model.

Maybe that's the way to do it. I need to think a bit more on this,
especially considering our (Samsung's) use cases.

Best regards,
Tomasz

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