linux-kernel - Re: [PATCH v2 1/2] gpio: Add driver for Zynq GPIO controller

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Message-ID: <CACRpkdY+3hy5iw=uRdmu665NWsoGacTMgjUq97219kEcfn7Dqw@mail.gmail.com>
Date:	Tue, 8 Jul 2014 11:27:57 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Baruch Siach <baruch@...s.co.il>
Cc:	Sören Brinkmann <soren.brinkmann@...inx.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexandre Courbot <gnurou@...il.com>,
	Harini Katakam <harinik@...inx.com>,
	Pawel Moll <pawel.moll@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Michal Simek <michal.simek@...inx.com>,
	Harini Katakam <harinikatakamlinux@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Rob Landley <rob@...dley.net>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	Harini Katakam <harini.katakam@...inx.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 1/2] gpio: Add driver for Zynq GPIO controller

On Mon, Jul 7, 2014 at 5:23 PM, Baruch Siach <baruch@...s.co.il> wrote:
> On Mon, Jul 07, 2014 at 04:51:56PM +0200, Linus Walleij wrote:

>> This needs someone to step in and provide a replacement, my preferred
>> mechanism would be a /dev/gpiochip0/... hierarchy using char devices.
>
> I really like the ability to control GPIOs from shell, both interactively and
> scripted. I find it useful for quick hardware level debugging,

I would be happy to carry it in the unstable-ABI debugfs for sure.
It's the supported ABI that bothers me.

> and for boot
> time scripting (mainly in initramfs).

What is the usecase here?

> Do you intend to preserve this
> capability in the future? Will I need a special utility (or Busybox applet) to
> do this with char device ioctl?

It is ABI so we have to preserve it. But sometimes people come with
new zuper-complex userspace usecases and want to add this or
that crazy ABI to do stuff in userspace that the kernel can do better.
And all that I intend to just NACK.

Yours,
Linus Walleij
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