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

[Johan Hovold <johan@kernel.org>]

On Tue, May 19, 2015 at 04:12:35PM +0200, Linus Walleij wrote:
> On Mon, May 18, 2015 at 5:17 PM, Grygorii.Strashko@linaro.org
> <grygorii.strashko@linaro.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