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

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Message-ID: <CACRpkdZgFMH07_W2eUWsgsUMXAJA1paEimAds=-XeViZaYySLA@mail.gmail.com>
Date:	Fri, 23 Aug 2013 20:45:49 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.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>,
	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 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));

Pass only the GPIO in the device tree and this works just fine.

The use case after that we do not interfer with.

Yours,
Linus Walleij
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