linux-kernel - Re: [PATCH v2 7/9] gpio: mockup: pass the chip label as device property

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Date:   Mon, 28 Sep 2020 16:52:25 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Bartosz Golaszewski <brgl@...ev.pl>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Kent Gibson <warthog618@...il.com>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        linux-doc <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/9] gpio: mockup: pass the chip label as device property

On Mon, Sep 28, 2020 at 4:00 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Mon, Sep 28, 2020 at 03:13:53PM +0200, Bartosz Golaszewski wrote:
> > On Mon, Sep 28, 2020 at 3:00 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > > On Mon, Sep 28, 2020 at 12:41:53PM +0200, Bartosz Golaszewski wrote:
> > > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > > >
> > > > While we do check the "chip-name" property in probe(), we never actually
> > > > use it. Let's pass the chip label to the driver using device properties
> > > > as we'll want to allow users to define their own once dynamically
> > > > created chips are supported.
> > > >
> > > > The property is renamed to "chip-label" to not cause any confusion with
> > > > the actual chip name which is of the form: "gpiochipX".
> > > >
> >
> > ^^^ here, see below
> >
> > > > If the "chip-label" property is missing, let's do what most devices in
> > > > drivers/gpio/ do and use dev_name().
> > >
> > > ...
> > >
> > > > +             snprintf(chip_label, sizeof(chip_label),
> > > > +                      "gpio-mockup-%c", i + 'A');
> > > > +             properties[prop++] = PROPERTY_ENTRY_STRING("chip-label",
> > > > +                                                        chip_label);
> > >
> > > You added new property, now count is up to 4. But at the same time
> > >
> > >         #define GPIO_MOCKUP_MAX_PROP  4
> > >
> > > how do you avoid overflow?
> > >
> >
> > I renamed the property, the previous "chip-name" is no longer used. In
> > fact it was never used but was accounted for in GPIO_MOCKUP_MAX_PROP.
>
> Either I'm missing something or...
>
> Current code in linux-next has 3 properties to be possible
>
> PROPERTY_ENTRY_U32("gpio-base", base);
> PROPERTY_ENTRY_U16("nr-gpios", ngpio);
> PROPERTY_ENTRY_BOOL("named-gpio-lines");
>
> You adding here
> PROPERTY_ENTRY_STRING("chip-label", chip_label);
>
> Altogether after this patch is 4 which is maximum, but since array is passed by
> a solely pointer, the terminator is a must.
>

Thanks for explaining my code to me. Yes you're right and I'm not sure
why I missed this. :)

I'll fix this in v3.

Actually this means the code is wrong even before this series - it's
just that we don't use the "chip-name" property.

Bartosz