linux-kernel - Re: [PATCH] gpiolib/arches: Centralise bolierplate asm/gpio.h

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Date:	Sat, 4 Feb 2012 17:41:15 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Guan Xuetao <gxt@...c.pku.edu.cn>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mike Frysinger <vapier@...too.org>,
	Haavard Skinnemoen <hskinnemoen@...il.com>,
	Hans-Christian Egtvedt <egtvedt@...fundet.no>,
	Grant Likely <grant.likely@...retlab.ca>,
	linux-arch@...r.kernel.org, linux-mips@...ux-mips.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
	linux-sh@...r.kernel.org
Subject: Re: [PATCH] gpiolib/arches: Centralise bolierplate asm/gpio.h

On Sat, Feb 04, 2012 at 06:06:32PM +0100, Sam Ravnborg wrote:
> On Sat, Feb 04, 2012 at 03:54:39PM +0000, Mark Brown wrote:
> > Rather than requiring architectures that use gpiolib but don't have any
> > need to define anything custom to copy an asm/gpio.h provide a Kconfig
> > symbol which architectures must select in order to include gpio.h and
> > for other architectures just provide the trivial implementation directly.
> 
> Hi Mark.
> 
> There is an even simpler solution.
> 
> For each arch that uses asm-generic/gpio.h add a line
> to arch/$ARCH/include/asm/Kbuild like this:
> 
> 
>     generic-y += gpio.h
> 
> This will then make this arch pick up the asm-generic version when
> you do #include <asm/gpio.h>.

You're assuming that asm-generic/gpio.h was invented to be a replacement
for an architecture asm/gpio.h.  Unfortunately, things aren't that
simple.

It would have been a lot better if asm-generic/gpio.h was tacked on the
bottom of linux/gpio.h - because that's what it really is.  It's core
code features, not platform stuff.

What's platform specific about asm/gpio.h is the number of GPIOs in
the system, and whether it wants to intercept the gpio_xxx() functions
to provide fast access to on-chip GPIOs.

What I'd suggest is moving asm-generic/gpio.h to linux/gpiolib.h, and
making asm-generic/gpio.h include that as a patch until stuff is fixed
for its new location.  That should result in a proper asm-generic/gpio.h
being:

/* The trivial gpiolib dispatchers */
#define gpio_get_value  __gpio_get_value
#define gpio_set_value  __gpio_set_value
#define gpio_cansleep   __gpio_cansleep
#define gpio_to_irq     __gpio_to_irq

and nothing else.

Alternatively, instead of linux/gpiolib.h, put it in linux/gpio.h instead,
but that gets more icky because of the mess of asm/gpio.h includes (which
I've been banging on for years about in ARM patches and they're _still_
coming.)
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