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

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Message-ID: <20200925122651.GA218809@sol>
Date:   Fri, 25 Sep 2020 20:26:51 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...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 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:
> 
> ...
> 
> > 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.
> 

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.

> ...
> 
> > > > +       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.
> 

Will do.  And in the debounce patch as well.

> > 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!

Cheers,
Kent.