linux-kernel - Re: GPIO bindings guidelines (Was: Re: [PATCH v5 10/12] gpio: Support for unified device properties interface)

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Date:	Thu, 23 Oct 2014 14:25:19 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: GPIO bindings guidelines (Was: Re: [PATCH v5 10/12] gpio: Support for unified device properties interface)

On Thursday 23 October 2014 15:02:46 Alexandre Courbot wrote:
> On Tue, Oct 21, 2014 at 4:54 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Tuesday 21 October 2014 14:14:02 Alexandre Courbot wrote:

> > Drivers that use
> > existing bindings with the "foo-gpio" form (or worse, "foo-somethingelse"
> > can use the same internal interface as the drivers that use name plus
> > index. Do you see a problem using what I suggested for the combined
> > API:
> >
> > __gpiod_get(dev, propname, index); // use property name plus index
> > gpiod_get(dev, index); // use "gpios" plus index
> > gpiod_get_named(dev, "name"); use "name-gpios" with index 0
> 
> Apart from the loosy naming practices which we sometimes see (and
> which should be caught during review), do you have something against
> requiring a name for all new GPIO bindings, i.e. for ensuring that all
> new properties are "name-gpio" and forbidding "gpios"?

Most other subsystems don't require a name, and traditionally we only
had anonymous indexed properties for a lot of things (registers, 
interrupts, ...).

I still like the idea of using anonymous references for simple things,
but if you and Linus feel that it's better to mandate names from now on,
I won't complain.

> Requiring a proper name for all GPIOs makes a lot of sense IMHO, it
> makes drivers easier to understand and is less error-prone than long
> arrays of GPIOs. The API would then be basically what we have today:
> 
> gpiod_get(dev, name) // use "name-gpios" with index 0
> gpiod_get_index(dev, name, index) // for the rare case where several
> GPIOs serve the same function. Not to be used lightly.
> 
> ... with stronger guidelines for the definition of new bindings, and a
> big warning in the kerneldoc of gpiod_get_index().
> 
> ACPI drivers that may use tables without _DSD should then use a way to
> bind GPIO names to indexes as a fallback for older hardware.

Ok.

	Arnd
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