linux-kernel - Re: [PATCH 0/4] gpio: introduce descriptor-based interface

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Message-Id: <201301141046.12976.arnd@arndb.de>
Date:	Mon, 14 Jan 2013 10:46:12 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Mike Frysinger <vapier@...too.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>, gnurou@...il.com,
	linux-m68k@...ts.linux-m68k.org,
	uclinux-dist-devel@...ckfin.uclinux.org
Subject: Re: [PATCH 0/4] gpio: introduce descriptor-based interface

On Monday 14 January 2013, Alex Courbot wrote:
> On 01/10/2013 07:08 PM, Arnd Bergmann wrote:
> > I found two that provide the generic gpio interfaces when gpiolib
> > is disabled, but use gpiolib otherwise for the same hardware,
> > arch/m68k/include/asm/mcfgpio.h and arch/blackfin/include/asm/gpio.h.
> > I would assume that we can simply remove the non-gpiolib shortcut
> > here at cost of a small overhead.
> 
> I performed a search on my side too (checking configurations options 
> which select GENERIC_GPIO but not ARCH_REQUIRE_GPIOLIB) and found the 
> same list. This takes some time btw - many platforms use this combo to 
> make GPIO support optional. Can I ask how you figured out these two archs?

I basically grepped for GENERIC_GPIO and looked at
the individual implementations.

> > Then there are a bunch that use gpiolib but have a nontrivial
> > implementation of gpio_get_value and other functions. I'm not sure
> > if these are a problematic with your code.
> 
> AFAICT these all implement an inline path that bypasses GPIOlib when the 
> GPIO number is known at compile time, for faster bitbanging I presume. 
> It should be totally harmless to keep them. Unfortunately, I don't think 
> it would be possible to have a similar trick using handlers.

Right, makes sense.

	Arnd
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