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 18:26:07 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Grant Likely <grant.likely@...aro.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>,
	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 18:25:01 Rafael J. Wysocki wrote:
> The problem is iteration over child nodes of a given one where there
> may not be struct device objects.
> 
> For example (from patch [2/16]):
> 
> +int acpi_for_each_child_node(struct acpi_device *adev,
> +                             int (*fn)(struct fw_dev_node *fdn, void *data),
> +                             void *data)
> +{
> +       struct acpi_device *child;
> +       int ret = 0;
> +
> +       list_for_each_entry(child, &adev->children, node) {
> +               struct fw_dev_node fdn = { .acpi_node = child, };
> +
> +               ret = fn(&fdn, data);
> +               if (ret)
> +                       break;
> +       }
> +       return ret;
> +}
> 
> and then fn() can be made work for both DTs and ACPI.  Without this we'd
> need to have two versions of fn(), one for DTs and one for ACPI (and possibly
> more for some other FW protocols), which isn't necessary in general (and
> duplicates code etc.). 
> 
> That actually is used by some patches down in the series (eg. [10/16]).
> 

Ok, I understand what you are doing now.

Looking at the example you point to (http://www.spinics.net/lists/devicetree/msg49502.html), I still feel
that this is adding more abstraction than what is good for us, and
I'd be happier with an implementation of gpio_leds_create() that
has a bit more duplication and less abstraction.

The important part should be that the driver-side interface is
sensible, other than that an implementation like

static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
{
	if (IS_ENABLED(CONFIG_OF) && pdev->dev.of_node)
		return gpio_leds_create_of(pdev);
	else if (IS_ENABLED(CONFIG_ACPI))
		return gpio_leds_create_of(acpi);
	return ERR_PTR(-ENXIO);
}

would keep either side of it relatively simple, by leaving out the
indirect function calls and new for_each_available_child_of_node()
macro.

How many other users of fw_dev_node do you have at the moment?

	Arnd
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