linux-kernel - Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs

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Date:	Mon, 11 Nov 2013 11:53:38 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Gerlando Falauto <gerlando.falauto@...mile.com>,
	Mark Brown <broonie@...nel.org>
CC:	Lars Poeschel <poeschel@...onage.de>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Grant Likely <grant.likely@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ian.campbell@...rix.com>,
	Kumar Gala <galak@...eaurora.org>,
	Pawel Moll <pawel.moll@....com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Enric Balletbo i Serra <eballetbo@...il.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Kevin Hilman <khilman@...aro.org>,
	Balaji T K <balajitk@...com>,
	Tony Lindgren <tony@...mide.com>,
	Jon Hunter <jgchunter@...il.com>
Subject: Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs

On 11/11/2013 11:28 AM, Gerlando Falauto wrote:
> 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?

(b) alone.

>From the perspective of the child interrupt controller, its output is
purely an interrupt. The fact that the parent interrupt controller could
use that pin as a GPIO in some other context (e.g. on a different board)
isn't something that the child interrupt controller should know/care about.
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