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

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Date:	Tue, 10 Sep 2013 13:53:47 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Lars Poeschel <poeschel@...onage.de>
CC:	Mark Brown <broonie@...nel.org>,
	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 09/10/2013 02:47 AM, Lars Poeschel wrote:
> On Tuesday 10 September 2013 17:19:24, 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).
> 
> And I say it again for those coming into the discussion late, like it has been 
> said many many times before: This patch does not break any of this drivers. 
> They simply request their GPIO from DT and turn it into an irq using 
> gpio_to_irq, request that irq on their behalf and use it as GPIO and IRQ in 
> parallel. At least this is not a problem.

Doesn't this patch call gpio_request() on the GPIO first, and hence
prevent the driver's own gpio_request() from succeeding, since the GPIO
is already requested? If this is not a problem, it sounds like a bug in
gpio_request() not ensuring mutual exclusion for the GPIO.
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