From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Warren <swarren@wwwdotorg.org>
Subject: Re: [PATCH v3] gpio: interrupt consistency check for OF GPIO IRQs
Date: Tue, 10 Sep 2013 16:34:20 -0600
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To: Mark Brown <broonie@kernel.org>
Cc: Lars Poeschel <poeschel@lemonage.de>, Javier Martinez Canillas <javier.martinez@collabora.co.uk>, Linus Walleij <linus.walleij@linaro.org>, Lars Poeschel <larsi@wh2.tu-dresden.de>, Grant Likely <grant.likely@linaro.org>, "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, Mark Rutland <mark.rutland@arm.com>, Ian Campbell <ian.campbell@citrix.com>, Kumar Gala <galak@codeaurora.org>, Pawel Moll <pawel.moll@arm.com>, Tomasz Figa <tomasz.figa@gmail.com>, Enric Balletbo i Serra <eballetbo@gmail.com>, Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>, Santosh Shilimkar <santosh.shilimkar@ti.com>, Kevin Hilman <khilman@linaro.org>, Balaji T K <balajitk@ti.com>, Tony Lindgren <tony@atomide.com>, Jon Hunter <jgchunter@gmail.com>
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On 09/10/2013 03:37 PM, Mark Brown wrote:
> On Tue, Sep 10, 2013 at 01:53:47PM -0600, Stephen Warren wrote:
> 
>> 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.
> 
> Or at the very least something that's likely to break in the
> future.

Looking at the GPIO code, it already prevents double-requests:

>         if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {
>                 desc_set_label(desc, label ? : "?");
>                 status = 0;
>         } else {
>                 status = -EBUSY;
>                 module_put(chip->owner);
>                 goto done;
>         }

And I tested it in practice, and it really does fail.