linux-kernel - Re: [Patch v2 2/2] gpio: Document GPIO hogging mechanism

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Date:	Tue, 2 Dec 2014 23:04:23 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Benoit Parrot <bparrot@...com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pantelis Antoniou <panto@...oniou-consulting.com>,
	Jiri Prchal <jiri.prchal@...ignal.cz>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [Patch v2 2/2] gpio: Document GPIO hogging mechanism

On Tue, Dec 2, 2014 at 7:57 AM, Benoit Parrot <bparrot@...com> wrote:
> Alexandre Courbot <gnurou@...il.com> wrote on Fri [2014-Nov-28 16:31:19 +0900]:
>> On Fri, Nov 21, 2014 at 8:54 AM, Benoit Parrot <bparrot@...com> wrote:
>> > Add GPIO hogging documentation to gpio.txt
>> >
>> > Signed-off-by: Benoit Parrot <bparrot@...com>
>> > ---
>> > Changes since v1:
>> >  * Split the devicetree bindings documentation in its own patch.
>> >
>> >  Documentation/devicetree/bindings/gpio/gpio.txt | 25 +++++++++++++++++++++++++
>> >  1 file changed, 25 insertions(+)
>> >
>> > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
>> > index 3fb8f53..82755e2 100644
>> > --- a/Documentation/devicetree/bindings/gpio/gpio.txt
>> > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt
>> > @@ -103,6 +103,24 @@ Every GPIO controller node must contain both an empty "gpio-controller"
>> >  property, and a #gpio-cells integer property, which indicates the number of
>> >  cells in a gpio-specifier.
>> >
>> > +The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
>> > +providing automatic GPIO request and configuration as part of the
>> > +gpio-controller's driver probe function.
>> > +
>> > +Each GPIO hog definition is represented as a child node of the GPIO controller.
>> > +Required properties:
>> > +- gpio-hog: a property specifying that this child node represent a gpio-hog.
>> > +- gpios: store the gpio information (id, flags, ...). Shall contain the
>> > +  number of cells specified in its parent node (GPIO controller node).
>> > +- input: a property specifying to set the GPIO direction as input.
>> > +- output-high: a property specifying to set the GPIO direction to output with
>> > +  the value high.
>> > +- output-low: a property specifying to set the GPIO direction to output with
>> > +  the value low.
>> > +
>> > +Optional properties:
>> > +- line-name: the GPIO label name. If not present the node name is used.
>> > +
>> >  Example of two SOC GPIO banks defined as gpio-controller nodes:
>> >
>> >         qe_pio_a: gpio-controller@...0 {
>> > @@ -110,6 +128,13 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
>> >                 reg = <0x1400 0x18>;
>> >                 gpio-controller;
>> >                 #gpio-cells = <2>;
>> > +
>> > +               line_b: line_b {
>>
>> Mmm what is the label used for? Can this node ever be referenced from
>> somewhere else?
>
> It's not used for anything else as far as I know other than as the line-name to be assigned to the gpio being hogged.
> I guess you agree with Linus and should make the line-name mandatory and remove the label altogether?
>
> I was trying to keep the verbosity to a minimum so as to have the possibilty to keep everything on a single line when possible.

It's just that when you see a label, you expect it to be referenced
somewhere, which is obviously not the case here. Just having

line_b {

would work just as well, wouldn't it?
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