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Subject: Re: [PATCH 3/4] rtc: ds1307: add calibration of_ for mt41txx chips.
To:     Rob Herring <robh+dt@kernel.org>
Cc:     Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@vger.kernel.org>, devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20180508145611.49072-1-giulio.benetti@micronovasrl.com>
 <20180508145611.49072-3-giulio.benetti@micronovasrl.com>
 <CAL_JsqKa7AF4x5440aVtCsCcvbTS85o-dRT8+Ka6QB=8zK2NzA@mail.gmail.com>
From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <201d77b1-ea75-90eb-8b30-da60529c70ba@micronovasrl.com>
Date:   Wed, 9 May 2018 20:33:56 +0200
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Hi Rob,

Il 08/05/2018 19:40, Rob Herring ha scritto:
> On Tue, May 8, 2018 at 9:56 AM, Giulio Benetti
> <giulio.benetti@micronovasrl.com> wrote:
>> m41txx chips can hold a calibration value to get really near to real
>> tick value.
> 
> Typo in the subject.
> 
>> Add calibration property(ranging between (-31) and 31), so on every probe
>> calibration value will be written to rtc.
>> This is because ic could loose supply due to low battery.
>>
>> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
>> ---
>>   .../devicetree/bindings/rtc/rtc-ds1307.txt    |  2 ++
> 
> Put all the binding changes in separate patch (or maybe 2: new
> compatible and new properties).
> 
>>   drivers/rtc/rtc-ds1307.c                      | 33 +++++++++++++++++++
>>   2 files changed, 35 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
>> index ce6469c1a516..d3d70a5495c5 100644
>> --- a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
>> +++ b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
>> @@ -34,6 +34,8 @@ Optional properties:
>>   - trickle-diode-disable : ds1339, ds1340 and ds 1388 only
>>          Do not use internal trickle charger diode
>>          Should be given if internal trickle charger diode should be disabled
>> +- calibration: m41t0, m41t00, m41t11 only
> 
> Needs a vendor prefix.
> 
> Calibration of what and what are the units?
> 
>> +       Set calibration value to correct external bias, ranging between (-31) and 31.
>>
>>   Example:
>>          rtc1: ds1339@68 {

This is not a problem anymore since I've used standard rtc sysfs 
"offset" instead of a dt-property as Alexandre pointed me out.

Thanks.

-- 
Giulio Benetti
CTO

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