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

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Message-ID: <52167E5D.6060802@wwwdotorg.org>
Date:	Thu, 22 Aug 2013 15:10:53 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Tomasz Figa <tomasz.figa@...il.com>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	Lars Poeschel <poeschel@...onage.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>, 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 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.

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