linux-kernel - Re: [PATCH 4/4] rtc: s3c: Fix RTC read on first boot

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Date:   Tue, 19 Oct 2021 18:19:45 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>, linux-rtc@...r.kernel.org,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] rtc: s3c: Fix RTC read on first boot

On 19/10/2021 18:04, Sam Protsenko wrote:
> On Tue, 19 Oct 2021 at 18:48, Alexandre Belloni
> <alexandre.belloni@...tlin.com> wrote:
>>
>> On 19/10/2021 16:17:24+0300, Sam Protsenko wrote:
>>> On first RTC boot it has the month register value set to 0.
>>> Unconditional subtracting of 1 subsequently in s3c_rtc_gettime() leads
>>> to the next error message in kernel log:
>>>
>>>     hctosys: unable to read the hardware clock
>>>
>>> That happens in s3c_rtc_probe() when trying to register the RTC, which
>>> in turn tries to read and validate the time. Initialize RTC date/time
>>> registers to valid values in probe function on the first boot to prevent
>>> such errors.
>>>
>>
>> No, never ever do that, the time is bogus and it has to stay this way,
>> else userspace can't know whether the time on the RTC is the actual wall
>> time or just some random value that you have set from the driver.
>>
> 
> Thought about that, but that error message looked distracting and not
> very helpful in understanding what's actually going on. Anyway, can
> you please drop this patch from series (and maybe [PATCH 3/4] too) and
> apply the rest?
> 

Please give it some time for review. Pinging after few hours is too fast.

Best regards,
Krzysztof