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From:   Bartosz Golaszewski <bgolaszewski@baylibre.com>
Date:   Mon, 8 Jul 2019 10:54:34 +0200
Message-ID: <CAMpxmJXZskz-cnqXVMRnUqxHjbQLwWZzQFrDc4eyGmronATCpg@mail.gmail.com>
Subject: Re: [PATCH v2] 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>, morgan.chang@vatics.com,
        "Stable # 4 . 20+" <stable@vger.kernel.org>
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pon., 8 lip 2019 o 07:23 Michael Wu <michael.wu@vatics.com> napisa=C5=82(a)=
:
>
> When a pin is active-low, logical trigger edge should be inverted to matc=
h
> the same interrupt opportunity.
>
> For example, a button pushed triggers falling edge in ACTIVE_HIGH case; i=
n
> ACTIVE_LOW case, the button pushed triggers rising edge. For user space t=
he
> IRQ requesting doesn't need to do any modification except to configuring
> GPIOHANDLE_REQUEST_ACTIVE_LOW.
>
> For example, we want to catch the event when the button is pushed. The
> button on the original board drives level to be low when it is pushed, an=
d
> drives level to be high when it is released.
>
> In user space we can do:
>
>         req.handleflags =3D GPIOHANDLE_REQUEST_INPUT;
>         req.eventflags =3D GPIOEVENT_REQUEST_FALLING_EDGE;
>
>         while (1) {
>                 read(fd, &dat, sizeof(dat));
>                 if (dat.id =3D=3D GPIOEVENT_EVENT_FALLING_EDGE)
>                         printf("button pushed\n");
>         }
>
> Run the same logic on another board which the polarity of the button is
> inverted; it drives level to be high when pushed, and level to be low whe=
n
> released. For this inversion we add flag GPIOHANDLE_REQUEST_ACTIVE_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 caught when the button is pushed.
> By the way, button releasing will emit a "falling" event. The timing of
> "falling" catching is not expected.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Michael Wu <michael.wu@vatics.com>
> ---
> Changes from v1:
> - Correct undeclared 'IRQ_TRIGGER_RISING'
> - Add an example to descibe the issue
> ---
>  drivers/gpio/gpiolib.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index e013d417a936..9c9597f929d7 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -956,9 +956,11 @@ static int lineevent_create(struct gpio_device *gdev=
, void __user *ip)
>         }
>
>         if (eflags & GPIOEVENT_REQUEST_RISING_EDGE)
> -               irqflags |=3D IRQF_TRIGGER_RISING;
> +               irqflags |=3D test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
> +                       IRQF_TRIGGER_FALLING : IRQF_TRIGGER_RISING;
>         if (eflags & GPIOEVENT_REQUEST_FALLING_EDGE)
> -               irqflags |=3D IRQF_TRIGGER_FALLING;
> +               irqflags |=3D test_bit(FLAG_ACTIVE_LOW, &desc->flags) ?
> +                       IRQF_TRIGGER_RISING : IRQF_TRIGGER_FALLING;
>         irqflags |=3D IRQF_ONESHOT;
>
>         INIT_KFIFO(le->events);
> --
> 2.17.1
>

Tested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>