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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Fri, 5 Jul 2019 14:50:24 +0200
Message-ID: <CAMpxmJVQhTeMa1dA+3ikW0Lbsp0BSajN=tO3VcQ3_GLt-=8OOw@mail.gmail.com>
Subject: Re: [PATCH] gpiolib: fix incorrect IRQ requesting of an active-low lineevent
To:     Michael Wu <Michael.Wu@vatics.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        linux-gpio <linux-gpio@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, mvp.kutali@gmail.com
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pt., 5 lip 2019 o 12:35 <Michael.Wu@vatics.com> napisa=C5=82(a):
>
> Hi Bartosz,
>
> For example, there is a button which drives level to be low when it is pu=
shed, and drivers level to be high when it is released.
> We want to catch the event when the button is pushed.
>
> In user space we configure a line event with the following code:
>
> req.handleflags =3D GPIOHANDLE_REQUEST_INPUT;
> req.eventflags =3D GPIOEVENT_REQUEST_FALLING_EDGE;
>
> and we hope to get "falling" events by reading the device node:
>
> while (1) {
>         read(fd, &dat,sizeof(dat));
>         if (dat.id =3D=3D 0) {
>                 printf("button pushed\n");
>         }
> }
>
> Run the same logic on another board which the polarity of the button is i=
nverted. The button drives level to be high when it is pushed.
> For the inverted level case, we have to add flag GPIOHANDLE_REQUEST_ACTIV=
E_LOW:
>
> req.handleflags =3D GPIOHANDLE_REQUEST_INPUT | GPIOHANDLE_REQUEST_ACTIVE_=
LOW;
> req.eventflags =3D GPIOEVENT_REQUEST_FALLING_EDGE;
>
> At the result, there are no any events been caught when the button is pus=
hed.
> By the way, button releasing will emit a "falling" event.
>
>
> Sincerely,
>
> Michael Wu

First: please don't top-post on the mailing list.

Second: have you even built the version you sent? Because I'm getting this:

drivers/gpio/gpiolib.c: In function =E2=80=98lineevent_create=E2=80=99:
drivers/gpio/gpiolib.c:963:4: error: =E2=80=98IRQ_TRIGGER_RISING=E2=80=99 u=
ndeclared
(first use in this function)
    IRQ_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
    ^~~~~~~~~~~~~~~~~~

And third: after fixing the define, this indeed looks like a bug and
I'll need to add a test for that to libgpiod once it's upstream.
Strange we didn't catch it before.

Please send a fixed version and add a Cc tag for stable. Nice catch!

Best regards
Bartosz Golaszewski