linux-kernel - Re: [RFC PATCH v2 07/16] gpio: Add support for unified device properties interface

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Date:	Tue, 23 Sep 2014 17:45:57 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Grant Likely <grant.likely@...aro.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Lee Jones <lee.jones@...aro.org>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [RFC PATCH v2 07/16] gpio: Add support for unified device properties interface

On Tuesday 23 September 2014 17:25:50 Linus Walleij wrote:
> On Tue, Sep 16, 2014 at 1:52 PM, Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> 
> > Some drivers need to deal with only firmware representation of its
> > GPIOs. An example would be a GPIO button array driver where each button
> > is described as a separate firmware node in device tree. Typically these
> > child nodes do not have physical representation in the Linux device
> > model.
> >
> > In order to help device drivers to handle such firmware child nodes we
> > add dev[m]_node_get_named_gpiod() that takes a firmware node pointer as
> > parameter, finds the GPIO using whatever is the underlying firmware
> > method, and requests the GPIO properly.
> >
> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> 
> I have a hard time figuring out if this is what we want for common
> accessors between DT and ACPI.
> 
> Can I get some input from Grant, Arnd, Mark, Darren...?

I just took a brief look at this. My first impression is that the
fw_dev_node structure is weird when all callers just do (in patch 2)

+	struct fw_dev_node fdn = {
+		.of_node = dev->of_node,
+		.acpi_node = ACPI_COMPANION(dev),
+	};

I'd much rather see an interface that passes the 'struct device'
pointer down to dev_get_named_gpiod() and all other exported
functions, and then internally does the conversion at the point
where the access is done.

	Arnd
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