Re: [PATCH v9 4/4] rtc: ds1307: add frequency_test_enable sysfs attribute to check tick on m41txx

[Giulio Benetti]

Il 20/07/2018 14:53, Andy Shevchenko ha scritto:
> On Thu, Jul 19, 2018 at 9:19 PM, Giulio Benetti
> <giulio.benetti@xxxxxxxxxxxxxxxx> wrote:
> > Hi Andy,
> >
> > Il 18/07/2018 18:26, Andy Shevchenko ha scritto:
> > > On Wed, Jul 18, 2018 at 5:06 PM, Giulio Benetti
> > > <giulio.benetti@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > > > > +       int ret;
> > > > > > +
> > > > > > +       ret = kstrtobool(buf, &freq_test_en);
> > > > > > +       if (ret == -EINVAL) {
> > >
> > >
> > > > > What kind of other error code you may expect and why they are not
> > > > > considered as no error?
> > >
> > >
> > > > According to documentation, kstrtobool can only fail with -EINVAL.
> > > > See:
> > > > https://elixir.bootlin.com/linux/v4.18-rc5/source/lib/kstrtox.c#L332
> > >
> > >
> > > That's correct. So, what do you want to show by explicitly mentioned
> > > an error code in the condition?
> >
> > So you mean I should check for negative values instead of specific error,
> > right?
>
> Learn from the existing code.
>
> As you found kstrtobool() returns either 0 (no error), or -EINVAL (the
> only possible error code for now).
> Checking ret for non-zero is enough.
> Thus,
>
> if (ret) {
>   ...
>   return ret;
> }
>
> should do a job.

Oh, I was pretty sure I've found an example of kstrtobool() in the way 
I've used, instead no.
Thanks for pointing me.
I correct it.

Best regards
Giulio