linux-kernel - Re: [PATCH 11/13] gpio: Support for unified device properties interface

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Date:	Wed, 08 Oct 2014 16:01:45 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 11/13] gpio: Support for unified device properties interface

On Wednesday, October 08, 2014 11:55:08 AM Alexandre Courbot wrote:
> On Wed, Oct 8, 2014 at 9:09 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > On Tuesday, October 07, 2014 07:52:02 PM Alexandre Courbot wrote:
> >> On Tue, Oct 7, 2014 at 7:40 PM, Mika Westerberg
> >> <mika.westerberg@...ux.intel.com> wrote:
> >> > On Tue, Oct 07, 2014 at 07:22:13PM +0900, Alexandre Courbot wrote:
> >> >> On Tue, Oct 7, 2014 at 9:18 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> >> > From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> >> >> >
> >> >> > 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]_get_named_gpiod_from_child() that takes a child firmware
> >> >> > node pointer as its second argument (the first one is the parent device
> >> >> > itself), 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>
> >> >> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >> >>
> >> >> ...
> >> >>
> >> >> > +/* Child properties interface */
> >> >> > +struct gpio_desc *dev_get_named_gpiod_from_child(struct device *dev, void *child,
> >> >> > +                                                const char *propname, int index);
> >> >> > +struct gpio_desc *devm_get_named_gpiod_from_child(struct device *dev, void *child,
> >> >> > +                                                 const char *propname, int index);
> >> >>
> >> >> I see the reason for these functions and am not opposed to them.
> >> >> However, I wonder if we could not replace propname by a con_id that
> >> >> would be resolved to one of con_id-gpio for DT and whatever naming
> >> >> convention ACPI is using?
> >> >
> >> > The code in gpio-leds.c and gpio_keys_polled.c refers to "gpios" as the
> >> > property name. If we can change that somehow to work with con_id-gpio
> >> > instead without breaking things, then why not.
> >> >
> >> >> This would prevent users to name GPIOs outside of the conventions
> >> >> defined in the bindings and be generally safer. Is there a particular
> >> >> reason (used by some old code?) for the current direct property
> >> >> access? If not, maybe we could call a slightly-modified of_find_gpio()
> >> >> to resolve the GPIO property for DT, and the equivalent function for
> >> >> ACPI?
> >> >
> >> > Only reason I can think of is support for the existing properties that
> >> > are used directly. Drivers using gpiod_get() and friends do not need
> >> > dev_get_named_gpiod_from_child() anyway.
> >>
> >> Right. Another thing is that the property handling code (active low
> >> only for now) is duplicated again, but that can be addressed
> >> separately.
> >>
> >> I will have a look at gpio-leds and gpio_keys_polled to see if we
> >> cannot make this work at a higher level. It's easier to have the
> >> bindings respected if the code itself enforces them.
> >
> > I'm wondering if that can be done after merging the current work?
> >
> > We'll be able to use the drivers in question with our hardware in the
> > meantime then ...
> 
> Yeah, that's probably ok. The properties in question already exist so
> we will have to support them anyway ; it's just a matter of seeing
> whether we can improve the proposed way.
> 
> So for now:
> 
> Acked-by: Alexandre Courbot <acourbot@...dia.com>

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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