linux-kernel - Re: [PATCH v2] gpio: interrupt consistency check for OF GPIO IRQs

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Date:	Mon, 26 Aug 2013 12:45:19 +0200
From:	Lars Poeschel <poeschel@...onage.de>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	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>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	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 v2] gpio: interrupt consistency check for OF GPIO IRQs

On Friday 23 August 2013 at 21:52:20, Stephen Warren wrote:
> On 08/23/2013 12:45 PM, Linus Walleij wrote:
> > On Thu, Aug 22, 2013 at 11:10 PM, Stephen Warren 
<swarren@...dotorg.org> wrote:
> >> On 08/21/2013 05:36 PM, Linus Walleij wrote:
> >>> On Thu, Aug 22, 2013 at 1:10 AM, Stephen Warren
> >>> <swarren@...dotorg.org> wrote: [Me]
> >>> 
> >>>>>> check if these in turn reference the interrupt-controller, and
> >>>>>> if they do, loop over the interrupts used by that child and
> >>>>>> perform gpio_request() and gpio_direction_input() on these,
> >>>>>> making them unreachable from the GPIO side.
> >>>> 
> >>>> What about bindings that require a GPIO to be specified, yet don't
> >>>> allow an IRQ to be specified, and the driver internally does
> >>>> perform gpio_to_irq() on it? I don't think one can detect that
> >>>> case.
> >>> 
> >>> This is still allowed. Consumers that prefer to have a GPIO
> >>> passed and convert it to IRQ by that call can still do so,
> >>> they will know what they're doing and will not cause the
> >>> double-command situation that we're trying to solve.
> >> 
> >> Why not? There are certainly drivers in the kernel which request a
> >> GPIO as both a GPIO and as an (dual-edge) interrupt, so that they
> >> can read the GPIO input whenever the IRQ goes off, in order to
> >> determine the pin state. This is safer against high-latency or lost
> >> interrupts.
> > 
> > Yes? Are we talking past each other here?
> > 
> > This is a perfectly OK thing to do as long as it is done like
> > this:
> > 
> > request_gpio(gpio);
> > gpio_direction_input(gpio);
> > request_irq(gpio_to_irq(gpio));
> 
> But I'm not aware that there's a rule saying it's illegal to:
> 
> request_irq(gpio_to_irq(gpio));
> request_gpio(gpio);
> gpio_direction_input(gpio);

But I'd consider this as a bug. What if the scheduler interrupts you right 
after you requested (and got assigned) the interrupt and another entity 
requests your gpio? Then you'd have a resource conflict, because you are 
not the owner of the gpio you requested an interrupt for.
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