linux-kernel - Re: [PATCH v9 09/20] gpiolib: cdev: support edge detection for uAPI v2

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Message-ID: <CAHp75Vd7Bmy5FWSputDCAAwSheH6ugszMyCcu1HOgC7BPVEX-w@mail.gmail.com>
Date:   Fri, 25 Sep 2020 12:35:49 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Kent Gibson <warthog618@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v9 09/20] gpiolib: cdev: support edge detection for uAPI v2

On Thu, Sep 24, 2020 at 6:07 AM Kent Gibson <warthog618@...il.com> wrote:
> On Wed, Sep 23, 2020 at 06:47:28PM +0300, Andy Shevchenko wrote:
> > On Tue, Sep 22, 2020 at 5:35 AM Kent Gibson <warthog618@...il.com> wrote:

...

> Also, this code is drawn from lineevent_irq_thread(), which is ordered
> this way.

Negative conditionals are slightly harder to read.

...

> > > +       if (!line->timestamp_ns) {
> > > +               le.timestamp_ns = ktime_get_ns();
> > > +               if (lr->num_lines != 1)
> > > +                       line->req_seqno = atomic_inc_return(&lr->seqno);
> > > +       } else {
> > > +               le.timestamp_ns = line->timestamp_ns;
> > > > +       }
> >
> > Ditto.
>
> Firstly, drawn from lineevent_irq_thread() which is structured this way.
>
> In this case the comment relates to the condition being true, so
> re-ordering the if/else would be confusing - unless the comment were
> moved into the corresponding body??

Yes.

...

> > > +       irq = gpiod_to_irq(line->desc);
> > > +       if (irq <= 0)
> > > +               return -ENODEV;
> >
> > So, you mean this is part of ABI. Can we return more appropriate code,
> > because getting no IRQ doesn't mean we don't have a device.
> > Also does 0 case have the same meaning?
>
> Firstly, this code is drawn from lineevent_create(), so any changes
> here should be considered for there as well - though this may
> constitute an ABI change??

For v1 probably, for v2 we are free to fix this.

> I agree ENODEV doesn't seem right here. Are you ok with ENXIO?

Yes.

> From gpiod_to_irq():
>
>                 /* Zero means NO_IRQ */
>                 if (!retirq)
>                         return -ENXIO;
>
> so it can't even return a 0 :-| - we're just being cautious.

I would drop = part then.

-- 
With Best Regards,
Andy Shevchenko