linux-kernel - Re: [PATCH v4 8/8] gpiolib: notify user-space about in-kernel line state changes

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Message-ID: <20241017142053.GB242458@rigel>
Date: Thu, 17 Oct 2024 22:20:53 +0800
From: Kent Gibson <warthog618@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v4 8/8] gpiolib: notify user-space about in-kernel line
 state changes

On Thu, Oct 17, 2024 at 04:14:24PM +0200, Bartosz Golaszewski wrote:
> On Thu, Oct 17, 2024 at 2:53 PM Kent Gibson <warthog618@...il.com> wrote:
> >
> > On Thu, Oct 17, 2024 at 10:14:16AM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > @@ -1447,8 +1450,6 @@ static long linereq_set_config(struct linereq *lr, void __user *ip)
> > >               }
> > >
> > >               WRITE_ONCE(line->edflags, edflags);
> > > -
> > > -             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> > >       }
> > >       return 0;
> > >  }
> >
> > I still get errors from this when reconfiguring lines with debounce.
> > You should leave this notify in place and use _nonotify when setting the
> > direction.
> > i.e.
> >
> > @@ -1436,11 +1432,11 @@ static long linereq_set_config(struct linereq *lr, void __user *ip)
> >                         int val = gpio_v2_line_config_output_value(&lc, i);
> >
> >                         edge_detector_stop(line);
> > -                       ret = gpiod_direction_output(desc, val);
> > +                       ret = gpiod_direction_output_nonotify(desc, val);
> >                         if (ret)
> >                                 return ret;
> >                 } else {
> > -                       ret = gpiod_direction_input(desc);
> > +                       ret = gpiod_direction_input_nonotify(desc);
> >                         if (ret)
> >                                 return ret;
> >
> > @@ -1450,6 +1446,8 @@ static long linereq_set_config(struct linereq *lr, void __user *ip)
> >                 }
> >
> >                 WRITE_ONCE(line->edflags, edflags);
> > +
> > +               gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> >         }
> >         return 0;
> >  }
> >
> > Given that, all my current tests are passing.
> >
>
> That looks good - after all we no longer notify from any place in
> gpiolib-cdev.c anymore - but I'd like to learn what's wrong exactly.
> Are you getting more events with debounce? Are you not getting any?
>

In linereq_set_config(), the notify comes from the gpiod_direction_input() -
before the edge_detector_setup() is called (not visible in the patch) and that
sets the debounce value in the desc.
So you get an event without the debounce set, or with a stale value.
Keeping the gpiod_line_state_notify() and using the _nonotify()
functions means the notify comes after the debounce has been set.

Cheers,
Kent.