linux-kernel - Re: [PATCH v2 2/2] gpiolib: check the 'ngpios' property in core gpiolib code

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Message-ID: <CAMRc=MdR_RGLLPJ5Hqetj5_7ZQfUXOijEoVp3uR7cgEDHKnchA@mail.gmail.com>
Date:   Thu, 18 Nov 2021 21:12:59 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] gpiolib: check the 'ngpios' property in core
 gpiolib code

On Thu, Nov 18, 2021 at 6:06 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Nov 18, 2021 at 02:23:17PM +0100, Bartosz Golaszewski wrote:
> > Several drivers read the 'ngpios' device property on their own, but
> > since it's defined as a standard GPIO property in the device tree bindings
> > anyway, it's a good candidate for generalization. If the driver didn't
> > set its gc->ngpio, try to read the 'ngpios' property from the GPIO
> > device's firmware node before bailing out.
>
> ...
>
> >       if (gc->ngpio == 0) {
> > -             chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
> > -             ret = -EINVAL;
> > -             goto err_free_descs;
> > +             ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
> > +             if (ret) {
> > +                     chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
> > +                     ret = -EINVAL;
> > +                     goto err_free_descs;
> > +             }
> > +
> > +             gc->ngpio = ngpios;
> >       }
>
> This should be
>
>         if (gc->ngpio == 0) {
>                 ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
>                 if (ret)
>                         return ret;

But device_property_read_u32() returning -ENODATA means there's no
such property, which should actually be converted to -EINVAL as the
caller wanting to create the chip provided invalid configuration - in
this case: a chip with 0 lines. In case of the non-array variant of
read_u32 that's also the only error that can be returned so this bit
looks right to me.

Bart

>
>                 gc->ngpio = ngpios;
>         }
>
>         if (gc->ngpio == 0) {
>                 chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
>                 ret = -EINVAL;
>                 goto err_free_descs;
>         }
>
> --
> With Best Regards,
> Andy Shevchenko
>
>