linux-kernel - Re: [RFC PATCH 1/2] pinctrl: Add output-disable

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Date:	Fri, 31 Oct 2014 09:49:35 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Sonny Rao <sonnyrao@...omium.org>,
	linux-rockchip@...ts.infradead.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Ivan T. Ivanov" <iivanov@...sol.com>,
	Sherman Yin <syin@...adcom.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [RFC PATCH 1/2] pinctrl: Add output-disable

On Tue, Oct 28, 2014 at 9:57 PM, Doug Anderson <dianders@...omium.org> wrote:
> The pinctrl bindings / API allow you to specify that:
> - a pin should be an output
> - a pin should have its input path enabled / disabled
>
> ...but they don't allow you to tell a pin to stop outputting.  Lets
> add a new setting for that just in case the bootloader (or the default
> state) left a pin as an output and we don't want it that way anymore.
>
> Signed-off-by: Doug Anderson <dianders@...omium.org>
(...)
> + * @PIN_CONFIG_OUTPUT_DISABLE: this will configure the pin _not_ to output.
> + *     Parameter should be 1.

This doesn't make sense. The pin is either low, high, some analog mode
or tristate/high impedance.

It does *not* stop existing.

Figure out the exact electronic meaning of what happens when you do
"output disable" in your hardware, I think it is very likely that
PIN_CONFIG_BIAS_HIGH_IMPEDANCE is what you are really
after here.

Yours,
Linus Walleij
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