linux-kernel - Re: [PATCH] gpiolib: fix incorrect IRQ requesting of an active-low lineevent

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Date:   Fri, 5 Jul 2019 14:50:24 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Michael Wu <Michael.Wu@...ics.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, mvp.kutali@...il.com
Subject: Re: [PATCH] gpiolib: fix incorrect IRQ requesting of an active-low lineevent

pt., 5 lip 2019 o 12:35 <Michael.Wu@...ics.com> napisał(a):
>
> Hi Bartosz,
>
> For example, there is a button which drives level to be low when it is pushed, 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 = GPIOHANDLE_REQUEST_INPUT;
> req.eventflags = 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 == 0) {
>                 printf("button pushed\n");
>         }
> }
>
> Run the same logic on another board which the polarity of the button is inverted. The button drives level to be high when it is pushed.
> For the inverted level case, we have to add flag GPIOHANDLE_REQUEST_ACTIVE_LOW:
>
> req.handleflags = GPIOHANDLE_REQUEST_INPUT | GPIOHANDLE_REQUEST_ACTIVE_LOW;
> req.eventflags = GPIOEVENT_REQUEST_FALLING_EDGE;
>
> At the result, there are no any events been caught when the button is pushed.
> 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 ‘lineevent_create’:
drivers/gpio/gpiolib.c:963:4: error: ‘IRQ_TRIGGER_RISING’ undeclared
(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