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Date: Mon, 11 Nov 2013 19:28:37 +0100
From: Gerlando Falauto <gerlando.falauto@keymile.com>
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To: Mark Brown <broonie@kernel.org>
CC: Stephen Warren <swarren@wwwdotorg.org>,
        Lars Poeschel <poeschel@lemonage.de>,
        Javier Martinez Canillas <javier.martinez@collabora.co.uk>,
        Linus Walleij <linus.walleij@linaro.org>,
        Lars Poeschel <larsi@wh2.tu-dresden.de>,
        Grant Likely <grant.likely@linaro.org>,
        "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ian.campbell@citrix.com>,
        Kumar Gala <galak@codeaurora.org>, Pawel Moll <pawel.moll@arm.com>,
        Tomasz Figa <tomasz.figa@gmail.com>,
        Enric Balletbo i Serra <eballetbo@gmail.com>,
        Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>,
        Santosh Shilimkar <santosh.shilimkar@ti.com>,
        Kevin Hilman <khilman@linaro.org>, Balaji T K <balajitk@ti.com>,
        Tony Lindgren <tony@atomide.com>, Jon Hunter <jgchunter@gmail.com>
Subject: Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs
References: <1377526030-32024-1-git-send-email-larsi@wh2.tu-dresden.de> <1521079.WSLhhfqBXl@lem-wkst-02> <52261BF0.4090106@wwwdotorg.org> <3144247.j2q6H0KWZx@lem-wkst-02> <52279524.8090006@wwwdotorg.org> <20130909161924.GT29403@sirena.org.uk>
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Hi everyone,

[jumping in on an old discussion]

On 09/09/2013 06:19 PM, Mark Brown wrote:
> On Wed, Sep 04, 2013 at 02:16:36PM -0600, Stephen Warren wrote:
>> On 09/04/2013 03:05 AM, Lars Poeschel wrote:
>
>>> The driver that tries to use the GPIO requested by this patch before HAS to
>>> fail. This is exactly the intention of this patch. We don't want the GPIO to
>>> be requested any more, if it is used as an interrupt pin.
>
>> That will break existing drivers. There are drivers that request the
>> same GPIO and IRQ. IIRC, the SDHCI CD (Card Detect) GPIO is requested
>> that way.
>
> Yes, plus input devices and audio jack detection among others.  This
> pattern is very common if the GPIO is actually being used as a GPIO, an
> edge triggered interrupt is used to flag when something happens and the
> state is determined by reading the GPIO state (often with some
> debounce).

I actually came across this thread while looking for an answer to the 
following (apparently trivial) question:

If you were to write a new driver & binding, what would be, in general, 
the recommended DT binding for a cascade interrupt controller (or any 
other peripheral, for that matter), which is connected through a GPIO 
(to be used as IRQ)?

a) Through gpios = <&gpio0 N>
b) through interrupt-parent = <&gpio0> & interrupts <N 
IRQ_TYPE_LEVEL_LOW>, or
c) both?

Thanks!
Gerlando