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From: Grant Feng <>
To: Alexandre Belloni <>
Subject: Re: [PATCH] rtc: interface^ 1969-12-31T23:59:59 is set as rtc_time if rtc_time is invalid in __rtc_read_time
Date: Sun, 2 Aug 2020 14:51:41 +0800
Message-ID: <> (raw)
In-Reply-To: <>


On 2020-08-01 21:28, Alexandre Belloni wrote:
> On 01/08/2020 19:20:07+0800, Grant Feng wrote:
>> 1969-12-31T23:59:59 is an error more clear than Invalid argument
> Definitively not, 1969-12-31T23:59:59 is a valid date and should not be
> returned when it is known the current date is not set in the RTC.
'rtc_valid_tm' is used to check rtc_time and 1969-12-31T23:59:59 is invalid.
when the RTC clock is not set, some rtc devices always return '0' or almost
random data, and different rtc devices may give different return data.
so, I think, it's usful to return a default date when the current date is
not set in the RTC.
>> For example, when the RTC clock is not set, it will print a kernel
>> error log every time someone tries to read the clock:
>>          ~ # hwclock -r
>>          hwclock: RTC_RD_TIME: Invalid argument
>> It's clear and easy to understand what happened if print
>> 1969-12-31T23:59:59 in this situation:
>>          ~ # hwclock -r
>>          Wed Dec 31 23:59:59 1969  0.000000 seconds
> How do you know this is an error an not what is actually set on the RTC?
'rtc_valid_tm' will check rtc_time when someone set the RTC, the time
should not be earlier than 1970-1-1T00:00:00. so 1969-12-31T23:59:59
can not be actually set on the RTC.
     When someone get
~ # hwclock -r
Wed Dec 31 23:59:59 1969  0.000000 seconds
     he knows: the RTC time doesn't match my watch, change it now.
but still lots of people don't know what happened if they see
~ # hwclock -r
hwclock: RTC_RD_TIME: Invalid argument

Grant Feng
Embedded Linux and Kernel engineering
RTCHIP Information Technology (Shanghai) Co., Ltd.

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Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-01 11:20 [PATCH] rtc: interface:: " Grant Feng
2020-08-01 13:28 ` Alexandre Belloni
2020-08-02  6:51   ` Grant Feng [this message]
2020-08-02 13:04     ` [PATCH] rtc: interface^ " Alexandre Belloni
2020-08-02 13:35       ` Grant Feng
2020-08-03  3:07       ` Grant Feng

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