Re: sysfs: wait for GPIO interrupt

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Tue, May 13, 2014 at 1:45 AM, Javier Martinez Canillas
<javier@xxxxxxxxxxxx> wrote:
> Hello Yegor,
> On Thu, May 8, 2014 at 10:19 AM, Yegor Yefremov
> <yegorslists@xxxxxxxxxxxxxx> wrote:
>> I've stumbled upon following issue. When waiting for interrupt with
>> poll() like described in this example [1], the program returns from
>> poll() immediately. This thread [2] describes a workaround for this
>> issue via making read() before invoking poll().
>>
>> My system is am335x, kernel 3.15-rc4
>>
>> I experience this behavior by both SoC's own GPIO and i2c expander tca6416.
>>
>
> I tested with an OMAP3 board which uses the same GPIO driver than the
> am335x and I was able to reproduce your issue.

At times like this I always want to warn you for using the GPIO sysfs
interface which is a scary piece of code.

And also to know what you are doing in userspace. Just hammering
GPIOs is already a bad idea, reading *interrupts* from GPIOs in
userspace is an even worse idea.

The basic rule is that the kernel shall handle hardware, and I just
get the feeling you are doing some userspace driver that should be
in the kernel instead.

Yours,
Linus Walleij
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