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

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Message-ID: <YZbCq5Xcohm/t/FP@smile.fi.intel.com>
Date:   Thu, 18 Nov 2021 23:16:27 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
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 09:12:59PM +0100, Bartosz Golaszewski wrote:
> 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.

So, what is so special about -EINVAL? Why -ENODATA is not good enough which
will exactly explain to the caller what's going on, no?

> >                 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;

When the caller intended to create a chip with 0 GPIOs they will get an error
as you wish with an error message.

> >         }

-- 
With Best Regards,
Andy Shevchenko