linux-kernel - Re: [PATCH]input: Change timer function to workqueue for gpio

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Date:	Thu, 25 Jun 2009 18:05:55 +0300
From:	Jani Nikula <ext-jani.1.nikula@...ia.com>
To:	ext Alek Du <alek.du@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Trilok Soni <soni.trilok@...il.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"ben-linux@...ff.org" <ben-linux@...ff.org>
Subject: Re: [PATCH]input: Change timer function to workqueue for gpio_keys
	driver

On Thu, 2009-06-25 at 16:52 +0200, Jani Nikula wrote:
> On Thu, 2009-06-25 at 16:08 +0200, ext Alek Du wrote:
> > If you schedule the timer when you decide it "stabilized", the final gpio_get_value()
> > could still return 0 in the timer handler, if the key released at that time. So your previous
> > "stabilized" state is useless.
> 
> True, gpio_keys_report_event should also compare the value to the
> previous state and bail out if it's unchanged. Something along the lines
> of:
> 
> @@ -46,6 +46,10 @@ static void gpio_keys_report_event(struct work_struct *work)
>  	unsigned int type = button->type ?: EV_KEY;
>  	int state = (gpio_get_value(button->gpio) ? 1 : 0) ^ button->active_low;
>  
> +	if (state == bdata->state)
> +		return;
> +	bdata->state = state; 

Actually scrap that, the input layer already ignores events with no
state changes, right?

> Debouncing should also completely ignore a single spike shorter than
> debounce_interval. Admittedly gpio-keys was flawed, but please consider
> a change like above which should fix that.

Same here, gpio-keys did ignore spikes shorter than debounce_interval.


BR,
Jani.


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