linux-kernel - Re: [PATCH] gpiolib: add GPIO_SET_DEBOUNCE

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Message-ID: <CAMRc=MdwSpWkgLTHN+6cOdG7aBAWWYFBC4+tfSNtA2HgX6s_3A@mail.gmail.com>
Date:   Wed, 29 Apr 2020 14:59:31 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Hector Bujanda <hector.bujanda@...i.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kent Gibson <warthog618@...il.com>
Subject: Re: [PATCH] gpiolib: add GPIO_SET_DEBOUNCE_IOCTL

śr., 29 kwi 2020 o 14:38 Linus Walleij <linus.walleij@...aro.org> napisał(a):
>
> On Wed, Apr 29, 2020 at 2:06 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:
>
> > I understand the need to set debounce time to make line events
> > reliable. As I see it: there'll be a couple steps to add this.
>
> I think there is a serious user-facing problem here though, because
> not all GPIO controllers supports debounce, so the call may return
> "nope" (error code).
>
> I think that is unavoidable with things like pull-up/down or drive
> strength, but for debounce I think we could do better.

For bias we don't return an error if the operation is not supported by
the driver.

> drivers/input/keyboard/gpio_keys.c contains generic
> debounce code using kernel timers if the GPIO driver
> cannot provide debouncing, and I have thought for a long
> time that it would be nice if we could do this generic, so that
> we always provide debouncing if requested, even for in-kernel
> consumers but most certainly for userspace consumers,
> else userspace will just start to reinvent this too.
>

Thanks for bringing this to my attention. This definitely looks like
something we could pull into gpiolib for others to use.

Bart