linux-kernel - Re: How about a gpio_get(device *, char *) function?

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Message-ID: <1908355.tpLPJU8MKg@percival>
Date:	Thu, 8 Nov 2012 15:14:34 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: How about a gpio_get(device *, char *) function?

On Thursday 08 November 2012 05:24:19 Linus Walleij wrote:
> I would prefer to create, e.g. in <linux/gpio/consumer.h>
> something like:
> 
> struct gpio;
> 
> struct gpio *gpio_get(struct device *dev, const char *name);
> 
> int gpio_get_value(struct gpio *g);
> 
> Nothing more! I.e. struct gpio is an opaque cookie, nothing to be known
> about it.
> 
> And then have the drivers using this *ONLY* include <linux/gpio/consumer.h>
> and not <linux/gpio.h>. So drivers have no clue what struct gpio is and
> will only operate on it using functions.
> 
> This follows the pattern set by Thomas Gleixner for e.g. IRQ descriptors,
> and the style was also used in the redesign of the struct clk *.

Also pretty similar to the regulator framework, which might itself have been 
inspired by IRQs and clocks.

> Of course the cross-referencing implementation can in e.g.
> drivers/gpio/gpiodev.c internally define that like this:
> 
> #include <linux/gpio.h>
> 
> /**
>   * @gpio: pointer to global GPIO number
>   */
> struct gpio {
>     int gpio;
> };
> 
> struct gpio *gpio_get(struct device *dev, const char *name)
> {
>    /* Lookup in cross-ref table etc */
> }
> 
> int gpioh_get_value(struct gpio *g)
> {
>    return gpio_get_value(g->gpio);
> }
> 
> (...)
> 
> Then we can work from there. I think it adds the proper
> opaqueness factor.

Looks nice, simple and to the point! Let's see if I can find the time to cook 
something based on this.

Thanks!
Alex.

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