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

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Date:   Tue, 12 May 2020 19:55:42 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>,
        "Bujanda, Hector" <Hector.Bujanda@...i.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH] gpiolib: add GPIO_SET_DEBOUNCE_IOCTL

On Mon, May 4, 2020 at 12:32 PM Bartosz Golaszewski <brgl@...ev.pl> wrote:

> Ideally we'd have to introduce new versions of gpioevent_request,
> gpioline_request, gpioline_info and gpioevent_data structs - this time
> with enough additional padding and no alignment issues. Then we could
> add the debounce properly.

Hm that sounds massive. Is it really that bad?

> This would of course add a lot of cruft to the uAPI code. I'd start by
> moving it out of drivers/gpio/gpiolib.c into a new file:
> drivers/gpio/gpiolib-cdev.c. This way we'd have everything related to
> the character device in one place. It would make it easier to: a) add
> a config option for disabling it entirely and b) add a config option
> to disable the v1 of the ioctl()s.

Its good to break out for code maintenance no matter what we do
with it :)

I would however not make it in any way totally optional, because the
big win with the character device over the legacy sysfs is to always
be available.

> Linus: about the software-debounce you mentioned: do you think it
> somehow plugs the hole we identified here?

Hm, I don't quite understand what the hole is I guess...

Linus