linux-kernel - Re: [PATCH v9 10/20] gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG

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Message-ID: <CAHp75Vd1=CpsMecw=dua66i-P992e71uQcOzWR7tvd6ZGyKWoA@mail.gmail.com>
Date:   Thu, 24 Sep 2020 11:26:49 +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 10/20] gpiolib: cdev: support GPIO_V2_LINE_SET_CONFIG_IOCTL

On Thu, Sep 24, 2020 at 6:24 AM Kent Gibson <warthog618@...il.com> wrote:
> On Wed, Sep 23, 2020 at 07:15:46PM +0300, Andy Shevchenko wrote:
> > On Wed, Sep 23, 2020 at 7:14 PM Andy Shevchenko
> > <andy.shevchenko@...il.com> wrote:
> > > On Tue, Sep 22, 2020 at 5:35 AM Kent Gibson <warthog618@...il.com> wrote:
> > > >
> > > > Add support for GPIO_V2_LINE_SET_CONFIG_IOCTL, the uAPI v2
> > > > line set config ioctl.
> >
> > > > +static long linereq_set_config_unlocked(struct linereq *lr,
> > > > +                                       struct gpio_v2_line_config *lc)
> > > > +{
> > > > +       struct gpio_desc *desc;
> > > > +       unsigned int i;
> > > > +       u64 flags;
> > > > +       bool polarity_change;
> > > > +       int ret;
> > > > +
> > > > +       for (i = 0; i < lr->num_lines; i++) {
> > > > +               desc = lr->lines[i].desc;
> > > > +               flags = gpio_v2_line_config_flags(lc, i);
> > >
> > > > +               polarity_change =
> > > > +                       (test_bit(FLAG_ACTIVE_LOW, &desc->flags) !=
> > > > +                        ((flags & GPIO_V2_LINE_FLAG_ACTIVE_LOW) != 0));
> > >
> > > Comparison
> >
> > Comparison between int / long (not all archs are agreed on this) and
> > boolean is not the best we can do.
> >
>
> There is no bool to int comparision here.

test_bit() returns int or long depending on arch... Then you compare
it to bool (which is a product of != 0).

> There are two comparisons - the inner int vs int => bool and the
> outer bool vs bool.  The "!= 0" is effectively an implicit cast to
> bool, as is your new_polarity initialisation below.
>
> > What about
> >
> >   bool old_polarity = test_bit(FLAG_ACTIVE_LOW, &desc->flags);
> >   bool new_polarity = flags & GPIO_V2_LINE_FLAG_ACTIVE_LOW;
> >
> >   old_polarity ^ new_polarity
>
> So using bitwise operators on bools is ok??

XOR is special. There were never bitwise/boolean XORs.

> > and move this under INPUT conditional?
> >
>
> It has to be before the gpio_v2_line_config_flags_to_desc_flags() call,
> as that modifies the desc flags, including the new polarity, so
> polarity_change would then always be false :-).

I really don't see in the code how polarity_change value is used in
FLAG_OUTPUT branch below.

> > > > +
> > > > +               gpio_v2_line_config_flags_to_desc_flags(flags, &desc->flags);
> > > > +               /*
> > > > +                * Lines have to be requested explicitly for input
> > > > +                * or output, else the line will be treated "as is".
> > > > +                */
> > > > +               if (flags & GPIO_V2_LINE_FLAG_OUTPUT) {
> > > > +                       int val = gpio_v2_line_config_output_value(lc, i);
> > > > +
> > > > +                       edge_detector_stop(&lr->lines[i]);
> > > > +                       ret = gpiod_direction_output(desc, val);
> > > > +                       if (ret)
> > > > +                               return ret;
> > > > +               } else if (flags & GPIO_V2_LINE_FLAG_INPUT) {
> > > > +                       ret = gpiod_direction_input(desc);
> > > > +                       if (ret)
> > > > +                               return ret;
> > > > +
> > > > +                       ret = edge_detector_update(&lr->lines[i],
> > > > +                                       flags & GPIO_V2_LINE_EDGE_FLAGS,
> > > > +                                       polarity_change);
> > > > +                       if (ret)
> > > > +                               return ret;
> > > > +               }
> > > > +
> > > > +               blocking_notifier_call_chain(&desc->gdev->notifier,
> > > > +                                            GPIO_V2_LINE_CHANGED_CONFIG,
> > > > +                                            desc);
> > > > +       }
> > > > +       return 0;
> > > > +}
> >
> > --
> > With Best Regards,
> > Andy Shevchenko



-- 
With Best Regards,
Andy Shevchenko