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

[Stephen Warren <swarren@wwwdotorg.org>]

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.