linux-kernel - Re: [PATCH] gpio: export 'debounce' attribute if supported by the gpio chip

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Message-ID: <CACRpkdYDLJDwv97Z0agZBbzCtEdeb5Y-83K2HkZRtLP1Cz_QiA@mail.gmail.com>
Date:	Fri, 7 Dec 2012 09:07:28 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH] gpio: export 'debounce' attribute if supported by the
 gpio chip

On Thu, Dec 6, 2012 at 7:32 AM, Guenter Roeck <linux@...ck-us.net> wrote:

> Create a 'debounce' attribute if debounce is supported by the gpio
> chip and a gpio pin is exported.
>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>

Can you describe the usecase for this?

I have this problem when working as a back-up GPIO maintainer that
I don't really understand the userspace apps doing this.

I would guess something like a userspace app reading a GPIO switch
and needing to set this to avoid key bounces, but it'd be nice to know
if this is really the case.

If this is the usecase I am slightly concerned why these are not used:
drivers/input/keyboard/gpio_keys_polled.c
drivers/input/keyboard/gpio_keys.c

The latter even uses the in-kernel debounce interface.

I'd agree if this is not user input at all but something like a switch
in a factory production line.

So please help me understand this.

Yours,
Linus Walleij
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