linux-kernel - Re: [PATCH 3/3] input: gpio-keys: Use hrtimer for software debounce

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Message-ID: <YEJ57PuEyYknR3MF@google.com>
Date:   Fri, 5 Mar 2021 10:35:24 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     od@...c.me, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] input: gpio-keys: Use hrtimer for software debounce

Hi Paul,

On Fri, Mar 05, 2021 at 05:01:11PM +0000, Paul Cercueil wrote:
> -static void gpio_keys_gpio_work_func(struct work_struct *work)
> +static enum hrtimer_restart gpio_keys_debounce_timer(struct hrtimer *t)
>  {
> -	struct gpio_button_data *bdata =
> -		container_of(work, struct gpio_button_data, work.work);
> +	struct gpio_button_data *bdata = container_of(t,
> +						      struct gpio_button_data,
> +						      debounce_timer);
>  
>  	gpio_keys_gpio_report_event(bdata);

I am not sure how this works. As far as I know, even
HRTIMER_MODE_REL_SOFT do not allow sleeping in the timer handlers, and
gpio_keys_gpio_report_event() use sleeping variant of GPIOD API (and
that is not going to change).

It seems to me that if you want to use software debounce in gpio keys
driver you need to set up sufficiently high HZ for your system. Maybe we
could thrown a warning when we see low debounce delay and low HZ to
alert system developer.

Thanks.

-- 
Dmitry