linux-kernel - Re: [PATCH] gpiolib: debugfs: display gpios requested as irq only

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Date:	Tue, 19 May 2015 17:39:40 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"Grygorii.Strashko@...aro.org" <grygorii.strashko@...aro.org>,
	Johan Hovold <johan@...nel.org>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: debugfs: display gpios requested as irq only

On Tue, May 19, 2015 at 04:12:35PM +0200, Linus Walleij wrote:
> On Mon, May 18, 2015 at 5:17 PM, Grygorii.Strashko@...aro.org
> <grygorii.strashko@...aro.org> wrote:
> > On 05/18/2015 06:08 PM, Johan Hovold wrote:
> 
> >>       GPIOs 160-191, platform/4805d000.gpio, gpio:
> >>       gpio-171 (<irq-only>          ) in  hi IRQ-209
> >
> > In general agree, but i propose to do it as
> >         GPIOs 160-191, platform/4805d000.gpio, gpio:
> >         gpio-171 ((null)          ) in  hi IRQ-209 <irq-only>
> >
> > My intention is - this interface could be considered as more or less stable, so
> > it is better to add additional information at the end of each line to avoid
> > potential breakage of User space SW (test/debug scripts).
> 
> What? If I wanted a stable interface I would use sysfs and document
> the ABI in Documentation/ABI/*.
> 
> debugfs is not ABI.

As I mentioned in my response to Grygorii, not everyone -- and most
notably apparently not even Linus Torvalds -- agrees on this:

	"The fact that something is documented (whether correctly or
	not) has absolutely _zero_ impact on anything at all. What makes
	something an ABI is that it's useful and available. The only way
	something isn't an ABI is by _explicitly_ making sure that it's
	not available even by mistake in a stable form for binary use.

	Example: kernel internal data structures and function calls. We
	make sure that you simply _cannot_ make a binary that works
	across kernel versions. That is the only way for an ABI to not
	form."

	https://lwn.net/Articles/309298/

In this case, it could be worked around by providing another debugfs
file with gpios used as IRQs, I guess.

Johan
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