linux-kernel - Re: [PATCH] gpiolib: notify user-space about line state changes triggered by kernel

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Message-ID: <CAMRc=McqgWLxDWG5AveDzTabHhaLnF2f36iAyzAx8ktVUMJj+Q@mail.gmail.com>
Date:   Thu, 24 Aug 2023 10:47:13 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: notify user-space about line state changes
 triggered by kernel

On Mon, Aug 21, 2023 at 12:43 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Fri, Aug 18, 2023 at 09:09:44PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>
> Interestingly why you keep submitter and author different...
>
> > We currently only emit CHANGED_CONFIG events when the user-space changes
> > GPIO config. We won't be notified if changes come from in-kernel. Let's
> > call the notifier chain whenever kernel users change direction or any of
> > the active-low, debounce or consumer name settings. We don't notify the
> > user-space about the persistence as the uAPI has no notion of it.
>
> ...
>
> > -     if (!ret)
> > +     if (!ret) {
> >               set_bit(FLAG_IS_OUT, &desc->flags);
> > +             blocking_notifier_call_chain(&desc->gdev->notifier,
> > +                                          GPIO_V2_LINE_CHANGED_CONFIG,
> > +                                          desc);
> > +     }
> >       trace_gpio_value(desc_to_gpio(desc), 0, val);
> >       trace_gpio_direction(desc_to_gpio(desc), 0, ret);
> >       return ret;
>
> The if (!ret) makes me a bit slower to understand as usual pattern to test
> for the errors first.
>
> That said, perhaps
>
>         if (ret)
>                 goto out_trace_event;
>
>         set_bit(FLAG_IS_OUT, &desc->flags);
>         blocking_notifier_call_chain(&desc->gdev->notifier,
>                                      GPIO_V2_LINE_CHANGED_CONFIG, desc);
>
> out_trace_event:
>         trace_gpio_value(desc_to_gpio(desc), 0, val);
>         trace_gpio_direction(desc_to_gpio(desc), 0, ret);
>         return ret;
>
> ...
>
> > +     ret = gpiod_set_config(desc, config);
> > +     if (!ret)
> > +             blocking_notifier_call_chain(&desc->gdev->notifier,
> > +                                          GPIO_V2_LINE_CHANGED_CONFIG,
> > +                                          desc);
> > +     return ret;
>
> Ditto.
>
>         ret = gpiod_set_config(desc, config);
>         if (ret)
>                 return ret;
>
>         blocking_notifier_call_chain(&desc->gdev->notifier,
>                                      GPIO_V2_LINE_CHANGED_CONFIG, desc);
>         return 0;
>

I agree with the latter but the former introduces an unnecessary goto
and looks worse IMO.

Bart

> --
> With Best Regards,
> Andy Shevchenko
>
>