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Subject: Re: [PATCH v9 4/4] rtc: ds1307: add frequency_test_enable sysfs
 attribute to check tick on m41txx
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Alessandro Zummo <a.zummo@towertech.it>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20180718094006.105675-1-giulio.benetti@micronovasrl.com>
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 <CAHp75VdSHdtJA5E=KvkUyij8CcgpyVO1b63-XBR7MnhVeWDpWA@mail.gmail.com>
From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <27a1d79b-7651-4896-58f7-73ff73b14c22@micronovasrl.com>
Date:   Fri, 20 Jul 2018 15:06:10 +0200
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Il 20/07/2018 14:53, Andy Shevchenko ha scritto:
> On Thu, Jul 19, 2018 at 9:19 PM, Giulio Benetti
> <giulio.benetti@micronovasrl.com> 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@micronovasrl.com> 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