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

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Date:   Fri, 25 Sep 2020 17:48:25 +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 Fri, Sep 25, 2020 at 3:26 PM Kent Gibson <warthog618@...il.com> wrote:
> On Fri, Sep 25, 2020 at 12:35:49PM +0300, Andy Shevchenko wrote:
> > 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:

...

> > > > > +       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.
> >
>
> Does that mean I should re-order and move the comment into the body?
> That would work for me - the normal case is line->timestamp_ns being
> set.

Yes, that's what I meant.

...

> > > 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.
> >
>
> ok, but you'd better not come after me in a subsequent review for not
> checking the 0 case!

For IRQ?! Maybe if I'll be drunk (quite unlikely).

I really don't like to check IRQ against 0. To me it should be
transparent to the caller. If IRQ == 0 in certain API or entirely in
Linux is considered NO_IRQ, then it should be either correctly handled
(means all following actions on it shouldn't fail, or it shouldn't be
returned in the first place).

-- 
With Best Regards,
Andy Shevchenko