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

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Date:	Mon, 11 Nov 2013 20:38:02 +0100
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Gerlando Falauto <gerlando.falauto@...mile.com>,
	Mark Brown <broonie@...nel.org>,
	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>,
	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 Monday 11 of November 2013 12:33:20 Stephen Warren wrote:
> On 11/11/2013 12:17 PM, Gerlando Falauto wrote:
> > Hi Stephan,
> > 
> > On 11/11/2013 07:53 PM, Stephen Warren wrote:
> >> 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.
> >>
> > 
> > Thanks for your answer. So it should be the parent driver to proactively
> > configure the GPIO as input, active high etc..., when an IRQ for its
> > GPIOs is requested, right?
> 
> That was the conclusion of this thread, or a similar thread, yes.

I would only add that settings, such as pull up/down control that depends
on the chip that drives the interrupt pin (i.e. the child interrupt
controller), are usually configured using pin control bindings.

Best regards,
Tomasz

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