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

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Message-ID: <52279082.5010105@wwwdotorg.org>
Date:	Wed, 04 Sep 2013 13:56:50 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Alexandre Courbot <acourbot@...dia.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>, gnurou@...il.com,
	linux-gpio@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [RFC 4/5] gpiolib: add gpiod_get() and gpiod_put() functions

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.
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