linux-kernel - Re: [RFC 4/5] gpiolib: add gpiod_get() and gpiod

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Message-ID: <CACRpkdY70r8mL8PSDmexr+_0Ddi-Y8x0RaDF-WWucZM9V8n=yw@mail.gmail.com>
Date:	Fri, 20 Sep 2013 20:40:48 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RFC 4/5] gpiolib: add gpiod_get() and gpiod_put() functions

On Wed, Sep 4, 2013 at 9:56 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 09/04/2013 05:29 AM, Alexandre Courbot wrote:
>> Add gpiod_get() and gpiod_put() functions that provide safer handling of
>> GPIOs.
>>
>> These functions put the GPIO framework in line with the conventions of
>> other frameworks in the kernel, and help ensure every GPIO is declared
>> properly and valid while it is used.
>
>> diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
>
>> +struct gpio_desc *__must_check gpiod_get(struct device *dev,
>> +                                      const char *con_id);
>> +void gpiod_put(struct gpio_desc *desc);
>
> It might be nice to add an "int index" parameter to this function. For
> example, a bit-banged parallel bus protocol driver might have 1
> chip-select GPIO, 1 clock GPIO, and 8 data GPIOs. gpiod_get(dev, "bus",
> 0)..gpiod_get(dev, "bus", 7) might be nicer than gpiod_get(dev,
> "bus0")..gpiod_get(dev, "bus7")? Possibly for client-simplicity,
> implement both gpiod_get(dev, con_id) (as an inline wrapper for ...) and
> gpiod_get_index(dev, con_id, index)?
>
> In DT terms, this would map to:
>
> cs-gpios = <&gpio 3 0>;
> clock-gpios = <&gpio 5 0>;
> bus-gpios = <&gpio 10 0 ... &gpio 17 0>;
>
> ... and with the mapping table registration mechanism, we could
> presumably add "int index" to struct gpiod_lookup.

This is an interesting usability aspect of the API, so I'd especially
like some input from the ACPI people on this as well.

Paging Mika, Rafael, Mathias.

Yours,
Linus Walleij
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