linux-kernel - Re: [RFC PATCH] gpiolib: Provide and export gpiod_export

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Message-ID: <CACRpkdZfRxNHGtZvzjn_vb2FGNPrvh1znWSGi0znN2_yHmz0Tw@mail.gmail.com>
Date:	Fri, 29 Aug 2014 07:44:02 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Alexandre Courbot <gnurou@...il.com>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [RFC PATCH] gpiolib: Provide and export gpiod_export_name

On Mon, Aug 11, 2014 at 5:20 PM, Alexandre Courbot <gnurou@...il.com> wrote:
> On Tue, Aug 12, 2014 at 12:15 AM, Guenter Roeck <linux@...ck-us.net> wrote:

>> This is just one of many patches which would make it possible to submit
>> the rest, which would make use of it. What you are saying is that it won't
>> make sense to submit that series into the kernel, because one of the very
>> first patches needed to enable that won't be accepted. Kind of a circular
>> argument, but I guess I'll have to live with it.
>
> Well I have not seen the other patches you mention and cannot guess
> their existence. If you send the full series it will of course be
> considered as such, but right now this lone patch does not hint any
> upstream user for this interface.
>
> Note that this doesn't change anything to the core of the argument ;
> we have not heard what Linus thinks about named GPIOs in
> /sys/class/gpio yet, maybe he will have a different opinion...

The sysfs is sort of broken by design because of things like this and
some other stuff.

I think the sysfs is scary, for example since it's not hierarchical
but flat and build on the assumption that there is one single
GPIO numberspace. As pointed out in some other message
in the thread it would be nicer to have:

/dev/gpiochip0/gpio0
/dev/gpiochip0/gpio1
....

instead of the horrid sysfs ABI that will have to maintain forever.

Still it is true that there is a precedent for named GPIOs in sysfs.

And in the end, userspace needs a way to figure out how to
get what it needs, a unique string is as good as anything.
I would be feeling better if userspace got that name from an
ioctl() on some /dev/* node than by plain filename search in
sysfs. I somewhat feel a named gpio in sysfs is more
helpful than just "gpio25".

But I'm not happy about merging the patch if Alexandre is
hesitant.

Yours,
Linus Walleij
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